Do-it-yourself low-frequency amplifier using tubes. Lamp unch. Amplifier ProLogue EL34: characteristics and reviews

People who love good music probably know about the Hi-End tube amplifier. You can do it yourself if you know how to use a soldering iron and have some knowledge of working with radio equipment.

Unique device

Hi-End tube amplifiers are a special class of household appliances. What is this connected with? Firstly, they have some pretty interesting design and architecture. In this model, a person can see everything he needs. This makes the device truly unique. Secondly, the characteristics of a Hi-End tube amplifier differ from alternative models that use Hi-End. The difference is that a minimum number of parts are used during installation. Also, when evaluating the sound of this device, people trust their ears more than nonlinear distortion measurements and an oscilloscope.

Selecting circuits for assembly

The preamplifier is quite simple to assemble. For it, you can choose any suitable scheme and start assembling. Another case is the output stage, that is, a power amplifier. As a rule, many different questions arise with it. The output stage has several types of assembly and operating modes.

The first type is a single-cycle model, which is considered a standard cascade. When operating in “A” mode, it has slight nonlinear distortion, but, unfortunately, has rather poor efficiency. Also noteworthy is the average power output. If you need to fully sound a fairly large room, you will need to use a push-pull power amplifier. This model can operate in “AB” mode.

In a single-ended circuit, only two parts are enough for the device to work well: a power amplifier and a pre-amplifier. The push-pull model already uses a phase inverted amplifier or driver.

Of course, for two types of output stage, in order to work comfortably with, it is necessary to match the high interelectrode resistance and the low resistance of the device itself. This can be done using a transformer.

If you are a connoisseur of “tube” sound, then you should understand that you need to use a rectifier, which is produced on a kenotron, to achieve such a sound. In this case, semiconductor parts cannot be used.

When developing a Hi-End tube amplifier, you don't have to use complex circuits. If you need to sound a fairly small room, then you can use a simple single-cycle design, which is easier to make and configure.

DIY Hi-End tube amplifier

Before starting installation, you need to understand some rules for assembling this type of device. We will need to apply the basic principle of installing lamp devices - minimizing fasteners. What does it mean? You will need to discard the mounting wires. Of course, this cannot be done everywhere, but their number must be minimized.

In Hi-End, mounting tabs and strips are used. They are used as additional points. This type of assembly is called hinged. You will also need to solder the resistors and capacitors that are on the lamp panels. It is highly not recommended to use printed circuit boards and assemble conductors so as to create parallel lines. This will make the assembly look chaotic.

Removing Interference

Later, you need to eliminate the low-frequency background, if, of course, it is present. Another important point is the choice of grounding point. In this case, you can use one of the options:

• The type of connection is a star, in which all “ground” conductors are connected to one point.
• The second method is to lay a thick copper busbar. It is necessary to solder the corresponding elements onto it.

In general, it is better to find a grounding point yourself. This can be done by determining the level of low-frequency background by ear. To do this, you need to gradually close all the grids of lamps that are located on the ground. If, when the subsequent contact is closed, the low-frequency background level decreases, then you have found a suitable lamp. To achieve the desired result, it is necessary to experimentally eliminate unwanted frequencies. You should also apply the following measures to improve the quality of your build:

• To make filament circuits for radio tubes, you need to use twisted wire.
• Tubes used in the preamplifier must be covered with grounded caps.
• It is also necessary to ground the housings with variable resistors.

If you want to power the preamp tubes, you can use DC current. Unfortunately, this requires connecting an additional unit. The rectifier will violate the standards of a Hi-End tube amplifier, since it is a semiconductor device that we will not use.

Transformers

Another important point is the use of different transformers. As a rule, power and output are used, which must be connected perpendicularly. This way you can reduce the level of low-frequency background. Transformers should be located in grounded enclosures. It must be remembered that the cores of each transformer should also be grounded. There is no need to use it when installing devices to avoid additional problems. Of course, these are not all the features associated with installation. There are quite a lot of them, and it will not be possible to consider them all. When installing a Hi-End (tube amplifier), you cannot use new element bases. They are now used to connect transistors and integrated circuits. But in our case they will not work.

Resistors

A high-quality Hi-End tube amplifier is a retro device. Of course, the parts for its assembly must be appropriate. Instead of a resistor, a carbon and wire element may be suitable. If you spare no expense in developing this device, you should use precision resistors, which are quite expensive. Otherwise, MLT models are applicable. This is a pretty good element, as evidenced by the reviews.

Hi-End tube amplifiers are also suitable for use with BC resistors. They were made about 65 years ago. Finding such an element is quite simple; you just need to walk around the radio market. If you are using a resistor with a power of more than 4 Watts, you need to choose enameled wire elements.

Capacitors

In a tube amplifier setup, you should use different types of capacitors for the system itself and the power supply. They are usually used to adjust the tone. If you want to get high-quality and natural sound, you should use a coupling capacitor. In this case, a small leakage current appears, which allows you to change the operating point of the lamp.

This type of capacitor is connected to the anode circuit, through which a large voltage flows. In this case, it is necessary to connect a capacitor that maintains a voltage greater than 350 volts. If you want to use quality parts, you need to use parts from Jensen. They differ from analogues in that their price exceeds 3,000 rubles, and the price of the highest quality radio elements reaches 10,000 rubles. If you use domestic elements, it is better to choose between the K73-16 and K40U-9 models.

Single ended amplifier

If you want to use a single-cycle model, you must first consider its circuit diagram. It includes several components:

• power unit;
• final stage;
• pre-amplifier in which the tone can be adjusted.

Assembly

Let's start the assembly with the pre-amplifier. Its installation follows a fairly simple scheme. It is also necessary to provide power control and a separator for tone control. It should be tuned to low and high frequencies. To increase shelf life, you need to use a multi-band equalizer.

In the laughter of the preamplifier you can see similarities with the common 6N3P double triode. The element we need can be assembled in a similar way, but use the final cascade. This is also repeated in stereo. Remember that the structure must be assembled on a circuit board. First it needs to be debugged, and then it can be installed on the chassis. If you installed everything correctly, the device should turn on immediately. Next you should move on to configuration. The value of the anode voltage for different types of lamps will differ, so you will need to select it yourself.

Components

If you do not want to use a high-quality capacitor, then you can use K73-16. It will be suitable if the operating voltage is more than 350 volts. But the sound quality will be noticeably worse. Electrolytic capacitors are also suitable for this voltage. You need to connect the C1-65 oscilloscope to the amplifier and submit a signal that will pass from the audio frequency generator. During the initial connection, you need to set the input signal to about 10 mV. If you need to know the gain, you will need to use the output voltage. To select the average ratio between low and high frequencies, it is necessary to select the capacitance of the capacitor.

You can see a photo of a Hi-End tube amplifier below. For this model, 2 lamps with an octal base were used. A double triode is connected to the input, which is connected in parallel. The final stage for this model is assembled on a 6P13S beam tetrode. This element has a built-in triode, which allows you to get good sound.

To configure and check the functionality of the assembled device, you must use a multimeter. If you want to get more accurate values, you should use a sound generator with an oscilloscope. When you have taken the appropriate devices, you can proceed to setup. At cathode L1 we indicate a voltage of about 1.4 Volts; this can be done if you use resistor R3. The output lamp current must be specified as 60 mA. To make resistor R8, you need to install a pair of MLT-2 resistors in parallel. You can use other resistors of different types. It should be noted that a rather important component is the decoupling capacitor C3. It was not in vain that it was mentioned, since this capacitor has a strong influence on the sound of the device. Therefore, it is better to use a proprietary radio element. Other elements C5 and C6 are film capacitors. They allow you to increase the quality of transmission of various frequencies.

A power supply built on the 5Ts3S kenotron is worth finding. It complies with all the rules for constructing the device. A homemade Hi-End tube power amplifier will have high-quality sound if you find this element. Of course, otherwise it is worth looking for an alternative. In this case you can use 2 diodes.

For a Hi-End tube amplifier, you can use the appropriate transformer, which was used in old tube technology.

Conclusion

To make a Hi-End tube amplifier with your own hands, you need to perform all the steps consistently and carefully. First, connect the power supply with the amplifier. If you configure these devices correctly, you can install a pre-amplifier. Also, using the appropriate technology, you can check all the elements to prevent damage. After assembling all the elements together, you can begin to design the device. Plywood may work well for the body. To create a standard model, it is necessary to place radio tubes and transformers on top, and regulators can already be mounted on the front wall. Using them you can enhance the tone and see the power indicator.

This was developed somewhere in the late 80s. During this time, it has proven itself to be worthy and versatile: it is suitable both for lovers of high-quality sound (I composed for myself) and for musicians who need power.

Brief lyrical introduction. At one time, the amplifier published in the magazine "Radio" in 1972 was very popular. I also repeated this pattern. Its disadvantages are known to many who repeated it: low linearity, weak stability at low frequency, insufficient stability at high frequency (which is why a corrective air conditioner was introduced into the circuit), a narrow frequency range, and something else that I don’t remember now. And most importantly, the sound left much to be desired.

I couldn’t stand this at home: my ears are not official :) The first thing I started the modernization with was replacing the output trance. The changes made to the output trance suggested themselves - to tighten the connection of the feedback windings (ultralinear) with the rest of the windings, to reduce Kg at higher frequencies, and to improve the frequency and phase characteristics of the output stage. In the version that I used in the new design, it was possible to expand the frequency range, increase HF stability, and lower the output impedance. The sound has noticeably improved, but now the entire circuit design (a clone of the so-called “Williamson circuit”) began to seem far-fetched in Hi-Fi - it was done somehow “head-on”, the weak link remained weak stability with OOS at infra-low frequencies, increased nonlinear and frequency distortions (especially at HF).

Further improvement resulted in the complete abandonment of this scheme. Many different circuit solutions were tried. Attempts to find the best option led to the solution that I propose. At the input, I used a cascode UA with high linearity, then a phase-inverted cascade with a divided load, which has the highest linearity. At the same time, I connected them directly to reduce phase shifts along the signal path. At the output, however, the familiar ultra-linear output stage remained with minor changes (for the purpose of ease of setup and increased stability), and, as already mentioned, with an improved output trance. In the diagram, I conventionally divided the preliminary stages, a bunch of triodes in which is actually my know-how ;), and the output stage, instead of which you can connect any suitable one. With a properly manufactured and adjusted amplifier, the maximum amplitudes on the control grids of the output lamps should be at least 80V at a load of 47k. And this made it possible to fully pump up the 6P45S. And what’s important is that, for all its advantages, the scheme turned out to be even simpler than the one we had to abandon.

The result is an amplifier with a sound that (with proper measures) can easily qualify for hi-end ;) The amplifier is absolutely stable, so it can be used both with deep OOS and without it at all - the linearity of all stages ensures low distortion and open loop OOS.

From two 6P3S, I managed to get >150 watts, from two 6P45S - >220 ;), and in the version with grid currents (especially for musicians) - 400 watts of peak power! But that diagram is already noticeably different from the one given.

I can’t give detailed parameters of the amplifier now - I haven’t measured it for a long time. For those who need sound and not parameters, I have given enough information for repetition, and if it is really necessary, I can (albeit at great cost) re-measure them. I would probably try it on for a magazine. And here it will do :o)

As for setup, it is simple:

1. assemble a standard parameter measurement scheme;
2. disable OOS;
3. turn on the power and warm up the cathodes;
4. resistors R10 and R11 set the quiescent currents of the output. lamps 30...60mA (0.06...0.12V at the cathodes), but always identical;
5. without supplying a signal to the input, use the R2 regulator to set the cathode of the bass reflex to 105V;
6. apply a signal to the input until the load voltage reaches 15 volts (for a 6-ohm variant);
7. resistor R9 sets the minimum of the 2nd harmonic at the output;
8. restore OOS (optional).

Point 7 can be skipped if you replace R8 and R9 with one with a resistance of 12k (this may not even affect the quality in any way, especially with OOS).

To power the amplifier, additional voltages were needed: 410V (10mA/channel) and stabilized 68V (b/t). The diagram shows one of the options for obtaining them from the available ones. Here you can do it in different ways. For example, I have a stub source. +220V to power the preamplifier, so I got +68 as a divider.

At one time, the scheme was shrouded in trade secrets :). Now please - let anyone who wants to try it. I repeat that the UN-FI combination is universal and can be used to drive various PP output stages (triode, pentode, class A, AB). For each specific case, you may have to recalculate some elements, which is done very easily. This is how I can help those in need.

P.S: Priboy amplifiers lend themselves well to such modifications - the quality improves noticeably.

List of radioelements

Designation	Type	Denomination	Quantity	Note	Shop	My notepad
	Radio lamp	6N1P	2			To notepad
	Radio lamp	6P45S	2			To notepad
C1, C5, C6	Capacitor	1 µF	3			To notepad
C2	Electrolytic capacitor	47 µF	1			To notepad
C3	Capacitor	0.1 µF	1			To notepad
C4	Capacitor	0.047 µF	1			To notepad
R1	Resistor	220 kOhm	1	0.5 W		To notepad
R2, R9	Trimmer resistor.	4.7 kOhm	2			To notepad
R3	Resistor	100 Ohm	1	0.5 W		To notepad
R3	Resistor	100 kOhm	1	2 W. By mistake in the circuit two resistors are named as R3		To notepad
R4	Resistor	2 MOhm	1	0.5 W		To notepad
R6	Resistor	1 MOhm	1	0.5 W		To notepad
R7	Resistor	12 kOhm	1	2 W		To notepad
R8	Resistor	10 kOhm	1	0.5 W		To notepad
R10, R11	Trimmer resistor	22 kOhm	2			To notepad
R12, R13	Resistor	47 kOhm	2	0.5 W		To notepad
R14, R15	Resistor	1 kOhm	2	0.5 W		To notepad
R16, R17	Resistor	22 kOhm	2	1 W		To notepad
R18, R19	Resistor	2 ohm	2	2 W		To notepad
R20	Resistor	2.7 kOhm	1	1 W		To notepad
R21, R22	Resistor	68 Ohm	2	2 W		To notepad
	Discharger		1

Single-channel UMZCH circuits

Complex circuits of tube amplifiers, in contrast to the simple ones already considered, include those UMZCHs in which at least three of the five following features are present in total: there is a pre-amplifier, the output stage is assembled according to a push-pull circuit, the amplification frequency band is divided into two or more channels, output power exceeds 2 W, the total number of lamps in one amplification channel is more than three. However, multi-channel schemes are not so often found in amateur radio work, although more often than our domestic industry did in past years. But even without this feature, the previous circuit of the Bulgarian Kusev was still not included in the list of complex ones, because it has only 2.5 lamps in one channel, the circuit is single-channel, and the output amplifier is single-ended.
But at first glance, a simpler circuit of a high-quality UMZCH from the collection of Gendin G.S. (MRB-1965) has enough distinctive features that it can be classified as complex (Fig. 12). The output power of an amplifier assembled on two 6FZP triode-pentode tubes exceeds 4 W, and the sound quality is beyond praise. The amplifier is designed for playing back recordings, so its input signal is 250 mV, the reproduced frequency band is 50...14000 Hz with an uneven frequency response of 1%, the nonlinear distortion coefficient does not exceed 2% at rated power.

Figure 12 Schematic diagram of a tube amplifier G.S. Gendina

The greatest difficulty when setting up tube power amplifiers with push-pull output is ensuring the symmetry of both amplification arms of the cascade. The designer is faced with several tasks that are complex in themselves, but taken together they cause a severe headache, because if they are left unresolved, then the advantages of the push-pull cascade turn into their opposite. Let me remind you of the advantages of the push-pull circuit. This is the absence of even harmonics in the load, which reduces the nonlinear distortion factor, and the absence of odd harmonics in the power supply circuit, which eases the requirements for blocking capacitors in the power supply filter and provides an additional margin of amplifier stability. Reducing the output capacitance of the lamps also contributes to stability, which significantly affects the operation of the UMZCH at high frequencies. And finally, with a push-pull connection of the lamps, the output impedance of the cascade increases, and this makes it possible to increase the quality factor of the circuit formed by the primary winding of the output transformer and a parallel capacitor, and improve the filtering ability of the load in relation to higher harmonics of the useful signal.
Let us consider the solution to the problem of realizing the advantages of a push-pull amplifier circuit using the example of this UMZCH. First, you need to select lamps L1 and L2, or rather their pentode parts, so that they have the same characteristics, in particular, input and output resistance and permeability, the equality of which allows us to hope for the coincidence of the static current-voltage characteristics of both lamps. Secondly, it is necessary to ensure a symmetrical DC mode, that is, the same anode supply and bias, and if it was not possible to select completely identical lamps, and this is guaranteed in most cases, then the mode must be selected so as to bring the characteristics of the lamps to identity. As can be seen in the diagram (Fig. 12), all mode elements and supply voltages of both arms are the same, but we emphasize once again that this is only possible if the characteristics of the lamps are identical. Adjusting the modes to complete symmetry is an independent task for everyone who is trying to repeat someone else's scheme. Thirdly, it is necessary to ensure symmetry of the load, which is the primary winding of the output transformer Tr1. To do this, wind the primary winding with a double wire in the amount of 1500 turns of PEV 0.15 wire on a Ш20хЗО core in 5 layers of 500 turns, interspersing them with 4 layers of a secondary winding of 24 turns each, for a total of 96 turns. The midpoint of the primary winding, to which the supply voltage is supplied, will be the connection of the initial ends of the wire, and the final terminals are connected to the anodes of the lamps. Fourthly, the excitation voltage is supplied to the control grids of both lamps of the output stage in antiphase, therefore, from the anode of triode L1, most of the signal is supplied directly to the grid of pentode L1, and part of it from the tuning resistor R12, which regulates the amplitude of the input signal on the grid of pentode L2, fed to the bass reflex - triode of lamp L2. In addition, in the grid circuit of pentode L2, to equalize the phase relationships when the input signal passes through non-identical circuits, the R9-C5 chain has been added. Now you can consider the push-pull cascade symmetrical and enjoy the sound quality.
However, that's not all. In order for the UMZCH to work even more stable at such output power values ​​​​that are limiting for 6FZP lamps, the entire amplifier is covered by OOS from the output to the cathode of the input triode L1 through the divider R7-R4, and from there to the grid through resistor R3. Local environmental protection systems are also available in each cascade. The filter in the power circuit C10-Dr1-C11 also commands respect, reducing the ripple factor of the anode voltage to 0.1%.

The next UMZCH for playing G. Krylov’s recordings is hardly more complicated than the previous one. Its output power is 6 W with a nonlinear distortion coefficient of 3%; at an output power of 4 W, the THD is 1%. Uneven frequency response in the range from 25 Hz to 16 kHz - 1 dB. Input sensitivity - 170 mV. Background level -55 dB. A special feature of the amplifier (Fig. 13), which consists of a pre-amplification stage, a push-pull output stage and a rectifier, is a unique excitation circuit for the final stage without the use of a phase inverter.

Figure 13 Schematic diagram of the Krylov tube power amplifier

The signal from the volume control R1 is fed to the control grid of the 6Zh1P type lamp, amplified by it and sent to the control grid of the 6P15P type output lamp L2. The signal voltage from the cathode of lamp L2 is further supplied to the cathode of lamp LZ.
The signal voltage U supplied to the LZ lamp can be determined from the formula:
U= (I1 - I2)(R7 + R8),
where I1 and 12 are the alternating components of the currents L2 and LZ. It is not possible to increase this voltage, since for good use of the LZ lamp, the current I must be close to 12, and it is impossible to increase the resistance of resistor R8 due to a decrease in the anode voltage. Therefore, this circuit is of interest only when using lamps with a high transconductance, operating at a low excitation voltage. Of the common lamps, the 6P15P pentode satisfies this requirement.
To reduce nonlinear distortion and reduce output impedance, the amplifier is covered by negative feedback with a depth of 14 dB. The feedback voltage is removed from the secondary winding of the output transformer and fed through a resistor to the cathode of lamp L1.
The power transformer is assembled on a core made of Ш32 plates, the thickness of the set is 32 mm, the window is 16x48 mm. The network winding contains 880, and the anode winding 890 turns of PEL 0.33 wire, the filament winding consists of 28 turns of PEL 0.8 wire.
The output transformer (Fig. 14) is made on a core made of Ш26 plates, the thickness of the set is 26 mm, the window is 13X39 mm. The primary winding contains 1200X 2 turns of PEV-2 0.19 wire, the secondary winding contains 88 x 3 turns of PEV-2 0.47 wire. It is necessary to strictly maintain the equality of the numbers of turns of the sections of the secondary winding and connect the sections in parallel.

Figure 14 Schematic diagram and winding diagram of the output transformer of a tube power amplifier by G. Krylov

The amplifier is mounted on a 1.5 mm thick aluminum chassis measuring 240x92X53 mm. The first stage should be as far as possible from the power and output transformers. The housing of potentiometer R1 should be connected to the chassis.
The distance between the power and output transformers must be at least 15 mm. The axes of their coils must be mutually perpendicular.
Setting up an amplifier comes down to adjusting the amount of feedback by changing the resistance of resistor R10. If the amplifier is excited, the terminals of the secondary winding of the output transformer should be swapped. To avoid self-excitation of the amplifier at ultrasonic frequencies, the feedback depth should not be more than 15 dB.
The bridge rectifier using D209 diodes can be replaced with a selenium rectifier ABC - 120-270. It is advisable to replace capacitors C5, Sb with one capacitor with a capacity of 150 μF for a voltage of 300 V. The loudspeakers of the acoustic unit should have a total impedance of 8-10 Ohms. The author used two 5GD10 loudspeakers connected in series.

The classic use of the properties of a push-pull circuit can be observed in the “simple* UMZCH K.H. Mikhailov (R-8/57). In this 6-watt amplifier (Fig. 15) at the input there is an L1 lamp - a 6N2P double triode, one half of which excites one arm of the final stage LZ and the second half of the same lamp L1, the latter in turn serves as a phase inverter for exciting lamp L2. By selecting resistors R6, R11, the mode for ensuring symmetrical excitation of the push-pull circuit is selected.

Figure 15 Schematic diagram of a tube power amplifier by K.Kh. Mikhailov

A special feature of the circuit is the presence of a separate tone control at the input of the UMZCH, the input voltage reaches 125 mV. In addition, to ensure the stability of the amplifier in a wide frequency range, frequency-dependent OOS R5, R11, R15-C9, R16-C10 has been introduced. Indicative of such a simple circuit is the use of a filament circuit of the final stage with symmetrical grounding of the midpoint, and for the input stage a reduced filament voltage of 5 V is used to reduce the level of internal noise of the L1 lamp. As in the previous circuit, the cathodes of both lamps of the final stage L2 and LZ are connected to one resistor R12, which provides additional adjustment of the symmetry of the mode.

Figure 16 Schematic diagram of a tube amplifier by F. Kuehne

Figure 16 shows a diagram of a relatively simple tube power amplifier with an ultralinear characteristic developed by the German specialist F. Kuehne. This device structurally combines an input switch, a pre-amplifier for an electromagnetic pickup with a low- and high-frequency filter, tone controls, as well as a final stage and a power supply. In the presence of a high-quality output transformer, the reproduced frequency band (with the tone controls set to the middle position) has a linear characteristic in the range from 50 to 30,000 Hz. At 30 Hz the output power drops slightly.
Input jacks 1, 2 and 3 are intended for connecting program sources that provide a signal with a voltage of about 500 mV, i.e., for supplying a signal from the linear output of a tape recorder, receiver, or from a piezoelectric pickup. Jack 4 is provided for connecting a high-quality electromagnetic studio pickup. It is connected to a two-stage pre-amplifier assembled on an L5 lamp. Depending on the position of switch P2, the amplifier can pass either the entire frequency band, or when capacitor C16 is turned on, only mid and high frequencies. The lower frequencies, at which vibrations of the electric motor can occur, which noticeably worsen the quality of playback of the recording, are cut off.
Capacitor C17 in the grid circuit of the right (according to the diagram) triode of lamp L5 and resistance R29 serve to raise lower sound frequencies. In position 5 of switch P1, capacitor C14 is switched on in parallel with capacitor C17, the rise in low frequencies is slightly reduced. In the first three positions of the switch, the grid of the right (according to the diagram) triode of the L5 lamp is shorted to ground, which allows the transmission of a radio program or magnetic recording to suppress interference from the input of the pickup. In position 4, capacitor C18 somewhat cuts off higher sound frequencies, in position 5 this effect is enhanced. Section P16 short-circuits inputs that are not currently in use. Consequently, when switch P1 is turned to positions 1-3, the inputs with the same digital designation are switched on in turn, in positions 4 and 5 - the fourth input (recording).
The tone controls (R2-R4) are placed in front of lamp L1, and the volume control R8 is behind it. The right triode of lamp L2 performs the function of a phase reflex, assembled according to a circuit with a divided load. The final stage using LZ and L4 lamps is assembled according to an ultra-linear circuit, which creates negative feedback in the circuit of shielding grids. The second negative feedback circuit goes from the secondary winding of the output transformer through resistance R20 to the cathode of lamp L2. The output transformer should be selected taking into account the existing loudspeaker.
Potentiometer R35 in the lamp filament circuit is designed to reduce the background level. In addition, resistances R36 and R37 in the filament circuit of lamp L1 reduce the filament voltage to 4.5 V, thereby reducing the level of noise and background. This, according to F. Kühne, is a somewhat unusual scheme, but for many radio amateurs of the Union, such as for Yu. Mikhailov (Fig. 15) already in 1957 (!), it was quite common, and was successfully used for a number of years in filament circuits of the first lamp of various amplifiers, while lowering the filament voltage did not affect the operation of the lamps.

Figure 17 Schematic diagram of a tube amplifier by A. Kuzmenko

The circuit of a high-quality 8 W tube low-frequency amplifier by A. Kuzmenko (R-5/57) is similar to the previous one in many respects, even the ratings of the individual circuits are the same. The author of this design (Fig. 17) believes that he has achieved improved sound quality by introducing a variety of feedbacks, including OOS on the screen grids through taps 16 and IB of the output transformer Tr1, general OOS through the divider R12-R30, local OOS in circuits excitation of all cascades.
A significant difference between this circuit and the previous one is the presence of a correction chain R14-C7 in the anode circuit of the left triode of lamp L2 according to the circuit. Using this chain, a reduction in the amplifier's frequency response in the high-frequency region is achieved, which arises due to the influence of several factors, the main ones of which can be considered the presence of local negative feedback, as well as the low quality of the output transformer Tr1.

Figure 18 Schematic diagram of the lamp UMZCH S. Matvienko

A later model of the broadband tube UMZCH S. Matvienko (Fig. 18) is even more complicated compared to the previous ones. To achieve high-quality sound in a 10-watt amplifier, in which the output stage operates at maximum power, the author of this design adds his own elements and circuits to the circuit, which help solve the problem - to achieve a high level of frequency response uniformity (no more than 0.1%) in wide frequency band 20...30000 kHz.
The amplifier is covered by an OOS loop, which operates in the mid-frequency region - this is the R5-R29-R12-C8 chain. In addition, all stages are covered by local feedback, and in this amplifier the pre-output stage, which creates symmetrical antiphase excitation, almost “literally” repeats the circuit of G. Krylov’s output stage (Fig. 13). However, already in the final stage we observe an additional adjustment R27 of the cathode resistance of the LZ, L4 lamps, thanks to which it is possible to harmonize the modes of both lamps; here, the OOS is implemented on the screen grids from part of the turns of the primary winding of the output transformer Tr1.
The circuit also uses all existing possibilities for controlling the timbre coloring of the sound signal. Separate tone control is provided at a level of 12 dB at high frequencies R14-C9, SY and 14 dB at low frequencies R15-C14, Dr1, and a fine-compensated volume control resistor R3 is also used.
For stable operation of the UMZCH, anode power with a low ripple coefficient is necessary, therefore, at the output of the rectifier it is necessary to install a U-shaped filter consisting of an inductor and two containers, as, for example, in the Kusev circuit (Fig. 9) or Gendin (Fig. 12).

Figure 19 Schematic diagram of the lamp UMZCH F. Kuehne

Next comes a series of developments by the aforementioned F. Kuehne. The circuit of a high-quality 10 W amplifier is shown in Fig. 19. Tone controls with separate control for high frequencies R1-C1, C2 and low frequencies R2, R3, R4 - SZ, C4 and volume control R5 are placed at the input of the amplifier, the sensitivity of which is about 600 mV.
The pre-amplification stage is assembled on a /11 tube. The upper (according to the circuit) triode of lamp L2 operates in amplification mode. Its control grid is connected directly to the anode of lamp L1 (there is no coupling capacitor). This eliminates the element of phase shift, which under certain conditions could cause instability of the negative feedback. Thanks to the direct connection, the control grid of lamp L2 is at the same high potential (+70 V) as the anode of lamp L1. Therefore, the voltage at the cathode of this lamp has to be increased to 71.5 V. The difference in voltage (1.5 V) is the required grid bias.
The control grid of the upper triode through resistance R12 is connected via direct current to the lower (according to the circuit) triode of lamp L2. As a result of this, and also due to the common resistance in the cathode circuit, the same bias voltage is applied to both triodes. The control grid of the lower triode through the capacitor SY is connected via alternating current to a common minus, i.e., the lamp is controlled not by the grid, but by the cathode (similar to a cascode circuit). Since the signal in the control grid circuit of the lower triode is phase-shifted by 180° relative to the control grid of the upper triode, voltages that are also phase-shifted by 180° are supplied to the terminal lamps. This method of phase rotation is characterized by high symmetry, good gain and the absence of phase distortion. The final stage circuit is usual.
The corrective circuit R6-C5, connected in parallel with the load resistance of lamp L1, and the filter in the negative feedback circuit, consisting of capacitor C8 and resistance R10, stabilize negative feedback in the ultrasonic frequency range.
For the pre-amplification stage, low-noise, highly stable resistances are selected, if possible. The values ​​of capacitor C8 and resistance R10 are selected taking into account the total beneficial resistance of the amplifier from the following table:

The output transformer is wound on an armor-type core made of transformer iron 0.5 mm thick without an air gap. The cross-section of the middle core rod is 28x28 mm. The primary winding consists of four sections, each with 1650 turns of PEL or PEV wire with a diameter of 0.11 mm. Spacers between layers of paper 0.03 mm thick. The secondary winding consists of two sections of 76 turns each, wound in two layers of wire of the same brand with a diameter of 0.6 mm with paper pads 0.1 mm thick.
The winding sequence is as follows. First, one of the sections of the primary winding is wound onto the frame, then half of the secondary winding, then two sections of the primary winding, then the other half of the secondary winding, and the fourth section of the primary winding is wound last. The two middle sections of the primary winding are connected in parallel and wound in one direction, and the rest in the opposite direction. Both extreme sections are also connected in parallel. The groups compiled in this way are included sequentially. Both halves of the secondary winding are also connected in series (with a speaker resistance of 16 Ohms).

Figure 20 Schematic diagram of another lamp UMZCH F. Kuehne

The next UMZCH F. Kühne for 20 W contains a bridge circuit for switching on the load in the final push-pull stage. In it, the constant component (Fig. 20) does not flow through the load, so the anode circuit is powered in addition to the output transformer, and it is a matching autotransformer.
The power transformer has two anode voltage windings (270 V each). The constant voltage on the electrolytic capacitors C9 and SY is 290 V, the voltage in the cathode circuit at idle is 18 V. It is noteworthy that the capacitors in the power supply are not connected to the case.
The bias voltage of the terminal lamps L2 and LZ is removed from the resistances in the cathode circuit R13 and R14. It is advisable to make one of them variable in order to be able to accurately adjust the symmetry in both end lamps. The voltage to the shielding grid of the lamp of one arm is supplied from the anode circuit of the lamp of the other arm. In the circuit of the shielding grid of the LZ lamp, a variable resistance R17 is included, which serves to suppress the background of the alternating current. In case of strong background noise, it is necessary to rephase one of the windings of the power transformer. Resistances R7, R10 and R12, R15 in the circuits of the control and shielding grids of the terminal lamps serve to protect against generation; they are soldered directly to the lamp panels.
The voltage at the cathode of lamp L1, the upper half of which operates in amplification mode, and the lower half serves to rotate the phase, is 28 V. The lower triode is controlled through the common resistance R5 in the cathode circuit, i.e., similar to the amplifier, the circuit of which is shown in Fig. 19. To obtain the same grid bias for both triodes, it would be possible, as in Fig. 19, to connect the control grid of the lower triode to the connection point of the resistances R1, R2, R5. Instead, in the circuit under consideration, a voltage divider R3, R4, C2 is used for the lower triode, which supplies a given voltage to the control grid and at the same time closes it to the chassis through capacitor C2. The capacitance of capacitor C2 was chosen to be large so that at lower frequencies OOS occurs and the gain at a frequency of 50 Hz is suppressed by 10% (the background becomes almost inaudible), and at a frequency of 20 Hz - by 50%. Below 20 Hz the gain decreases sharply. This design of the circuit sometimes causes some bewilderment if we say that the amplifier should pass the widest possible frequency band. However, a radio amateur who has experience with high-quality amplifiers is familiar with their vagaries. A tone with a frequency of 20 Hz is practically not audible. Moreover, lower frequency tones are not audible. If our “too good” amplifier is excited at very low frequencies that are not perceptible to the ear, then as a result of cross-modulation with the tones being listened to, interference may arise that greatly distorts the sound picture.
The final stage of the amplifier is covered by negative feedback. The optimal load of the final stage is about 800 Ohms. However, even with a different load (for example, at 600 or 1600 ohms), the audio output power is 17.5 W. The quality of the output autotransformer Tr1 is not subject to such great demands as for conventional push-pull stages. Each lamp operates on an entire winding, and since the AC lamps are connected in parallel, the total winding resistance is reduced to 25% of the nominal value. In order to obtain complete symmetry and ground the output terminal, the middle tap of the winding is connected to the chassis. This clamp simultaneously serves as the neutral wire of the voice coil winding, which forms part of the common winding of the autotransformer.

Figure 21 Location of windings on the transformer frame

Figure 21 shows the location of the windings on the frame of the autotransformer Tr1. The core consists of transformer iron plates assembled without clearance. The cross section of the middle core rod is 7.3 cm2. Winding I contains 650 turns of PEL 0.35 wire; winding IV - 490 turns of the same wire; winding II contains 119 turns of PEL 1.0 wire; winding 111-41 turns of the same wire.

Another circuit of a high-quality 20 W terminal lamp UMZCH by F. Kuehne is shown in Fig. 22. Basically, this amplifier repeats the previously discussed circuit solutions, which provide high-quality sound reproduction, but as a final amplifier it does not contain volume and tone controls, and it also provides the ability to connect speakers with different load resistance ratings. In the switch position, as shown in the diagram, the resistance of the dynamic heads is 16 Ohms. Below the diagram are the switch positions for 8 Ohm (left) and 4 Ohm.

Figure 22 Schematic diagram of a 22 W amplifier by F. Kuehne

In all of the listed Kuehne schemes, foreign-made lamps are used, the procedure for replacing which with domestic ones is given at the end of the book in a special table.
To ensure increased power of the output amplifier while maintaining high-quality sound, a parallel connection of output stage lamps in each arm of a push-pull circuit is often used, as was done in the 20-watt final UMZCH V. Bolshoi (R-7/60).

The amplifier circuit (Fig. 23) has only two stages - an input phase inverter on a 6N2P double triode tube and an output final stage on four 6P14P tetrode tubes. All cathodes of the output lamps L2...L5 are connected at one point on the cathode auto-bias chain resistor R12-C6, and the DC tetrodes themselves are connected as triodes. This somewhat reduces the steepness of the current-voltage characteristic, but makes it more linear.

Figure 23

In the anode power circuit, instead of the L6 kenotron, it is better to install a bridge of semiconductor diodes with a reverse voltage of 400 V and a forward current in the open state of 0.5 A, and also add a U-type smoothing filter. By the way, the filter choke is best made on a toroidal core and covered with a grounded shield. Power transformer Tr2 is standard with a power of 200 W.

Similar in circuit design, but more powerful, the 100 W V. Shushurin UMZCH (MRB-1967) is designed to work with the equipment of an ensemble of electric musical instruments, and can also be used for sounding small halls and club rooms.
The rated output power of the amplifier is 100 W. The harmonic coefficient at a frequency of 1000 Hz is no more than 0.8%, at frequencies of 30 and 18000 Hz - no more than 2%. In the frequency range 30-18000 Hz, the unevenness of the frequency response is +1 dB. Nominal sensitivity 500 mV, nominal output voltage at a load of 12.5 Ohms - 35 V. The noise level of the amplifier relative to the nominal output level is about -70 dB. Power consumption from the network is 380 VA.

Figure 24 Schematic diagram of a 100 W tube amplifier by V. Shushurin

The schematic diagram of the power amplifier is shown in Fig. 24. The first two stages are made using lamps L1 and L2a. The second triode of a 6N6P (L26) lamp is used in a phase-inverted stage with a divided load (R10 and R12). The final stage of the amplifier is assembled according to a push-pull circuit using lamps LZ, Lb, and to provide the necessary power, two lamps are connected in parallel in each arm.
To obtain a uniform frequency response and low nonlinear distortion, the last three stages of the amplifier are covered by deep negative voltage feedback. The feedback voltage is removed from the secondary winding of the output transformer Tr2 and is fed through the R19C8 chain to the cathode circuit of the lamp L2a.
Lamps L8-L6 of the final stage operate in AB mode. The negative bias to their control grids is supplied from a separate source - a half-wave rectifier on diode D7.
The anode circuits of the terminal lamps are powered by a full-wave rectifier using diodes D6-D13 connected in a bridge circuit, and the shielding grids of these lamps and the anode circuits of lamps L1 and L2 are powered by a rectifier using diodes D2-D5. Rectifier filters are capacitive. The capacitance of the filter capacitors is chosen such that when the power supplied by the amplifier changes from zero to the rated value, the supply voltage changes by no more than 10%.
The power amplifier in the form of a separate, electrically and structurally complete unit is mounted on a metal chassis with dimensions 490X210X70 mm. All vacuum tubes, transformers and electrolytic capacitors are installed on top of the chassis. The remaining parts are mounted in the chassis basement.
The power transformer is made on a Sh32X80 magnetic conductor. window 32X80 mm.
Winding 1-2, designed for a mains voltage of 220 V, contains 374 turns of wire PEV-1 1.0, winding 5-4-85 turns of wire PEV-1 0.25, winding 5-6-790 turns of wire PEV-1 0 .55, winding 7-5-550 turns of wire PEV-1 0.41, winding 9-10-11 turns of wire PEV-1 0.9, windings L-12 and 13-14 - 11 turns of wire PEV-1 1 ,4. The location of the windings on the power transformer frame is shown in Fig. 25.

Figure 25 Location of windings on the frame of V. Shushurin’s tube amplifier

The output transformer Tr2 is made on the same magnetic conductor as the power transformer. The windings are sectioned. The layout of the winding sections on the frame is shown in Fig. 25.6. Primary winding 1-3 consists of four sections of PEV-1 0.55 wire, 450 turns in each section. The sections are connected in series, and a tap is made from the middle (pin 2). The secondary winding 4-5 consists of ten sections of PEV-1 0.55 wire connected in parallel, 130 turns in each section.
Provided that installation is correct, pre-tested parts are used and the output transformer is manufactured according to the recommended circuit, setting up a power amplifier comes down to setting the required bias voltage of the output stage lamps (-35 V) with trimming resistor R41 and balancing the arms of the lamps of this stage with resistor R14. It must be remembered that you cannot turn on the power amplifier without a load, as this may cause an electrical breakdown between the windings of the output transformer."

High sound quality is also ensured by a stationary type power amplifier, given by G. Gendin in the book “Homemade ULF”, MRB-1964. By a strange coincidence, the circuit of this amplifier (Fig. 26) is very similar to the standard 10-watt Kinap company, which was in every radio unit in the 60-70s, except that the lamps were replaced from 6CCDs to more modern ones. The circuit of the phase inverter and output stage is similar to that discussed above (Fig. 12), and the preliminary stages on lamps L1, /12 accelerate the final amplifier to such power that, in the presence of deep feedback through R26-R34, provide the rated output power.

Figure 26 Tube power amplifier G.Genedin

This amplifier is distinguished by its complete functionality, it has all the necessary adjustments, you can connect any sound source at the input, be it a microphone, a pickup, a tape recorder, a radio, a TV or a radio broadcast line. At the output, you can connect any of the available types of dynamic heads, for which switch P2 is provided in the secondary winding of the output transformer Tr2.
The anode circuits are powered at a low level of ripple thanks to the presence of a C12-Dr1-C13 filter, all midpoints of the filament windings are through trimming resistors R19, R23, and they are also supplied with a 27 V bias through a divider R16-R17. In the B1 rectifier you can use diodes of the D226 or D7Zh type.

High-quality UMZCH N. Zykova (R-4/66) uses tone controls for low and high frequencies and tone controls for three fixed mid frequencies (each of which differs from the previous one by approximately an octave f = 2f2 = 4f3), which allows you to get almost any frequency response of the sound reproduction channel, and also significantly increases the possible degree of correction of the amplifier characteristics at higher and lower frequencies (up to 30-40 dB). In addition, the use of midrange controls greatly simplifies the design and construction of speaker systems for high-quality sound reproduction.
The rated output power of the amplifier is 8 W. The maximum sensitivity from the pickup sockets is 100-200 mV, from the linear output -0.5 V, from the broadcast line -10 V. The amplifier reproduces an audio frequency band from 40 Hz to 15 kHz with unevenness at the edges of the range of 1.5 dB (without controls timbre).

Figure 27 Schematic diagram of an 8 W tube power amplifier N. Zykova

Figure 28 Scheme and variant of winding the output transformer for a tube amplifier by N. Zykov

Nonlinear distortion factor at a frequency of 1 kHz at rated output power - 0.5%; with an output power of 6W - 0.2%. The active load resistance of the amplifier is 4 Ohms, the noise level is 60 dB. The output impedance of the amplifier is 0.3...0.5 Ohm. The amplifier can be powered from an AC mains voltage of 110, 127 and 220 V, power consumption from the mains is 120 W.
A switching device is connected to the input of the amplifier (see Fig. 27), with the help of which a receiver P (100 mV), a TV T (100 mV), an audio cartridge, a linear output of a tape recorder M (0.5 V), and a broadcast line can be connected to it L (10...30 V), as well as the tape recorder input (to the linear output of the LV amplifier).
The first stage of the amplifier is assembled on the L1a lamp, it is used to amplify signals coming from the sockets of the pickup, receiver P or TV T. The next two stages, assembled on the L2 lamp, include standard tone controls for low and high frequencies of type II (potentiometers R7 and R10) and a midrange tone control (potentiometers R22, R23 and R 24).
To reduce the noise level, the incandescent circuits of lamps L1 and L2 connected in series are powered by a low-voltage rectifier.
An amplifier of the pre-final stage and a bass reflex are mounted on the LZ lamp. Good symmetry with minimal distortion in the case of large control signals is achieved by using a relatively low-resistance anode and cathode load in the inverter phase.
The final stage of the amplifier is push-pull, it is assembled according to an ultra-linear circuit. The last three stages of the amplifier are covered by deep negative feedback, the voltage of which is removed from the secondary winding of the output transformer and fed into the cathode circuit of the LZ lamp.
Power transformer Tr1 is assembled on a core made of Ш20 plates, the thickness of the set is 45 mm. The network winding contains 2x(50+315) turns of PEL 0.38 wire, the boost winding contains 700 turns of PEL 0.29 wire. The winding of the low-voltage rectifier consists of 45 turns of the same wire, and the incandescent winding of the lamps consists of 17 + 4 turns of PEL 1.0 wire.
The Dr1 filter choke with an inductance of 4 H is wound on a core made of USh16 plates, the thickness of the set is 15 mm, its winding contains 2300 turns of PEL 0.25 wire. Coil L1 = 6.5 - wound on a core made of USh12 plates, the thickness of the set is 18 mm, its winding consists of 3100 turns of PEL 0.14 wire. Coils L2 and L3 are made on armored cores of the SB-4a type. The coils are wound in bulk on cylindrical frames made of ebonite or textolite and contain 2200 turns of PEV-2 0.1 wire (inductance 0.35...0.4 H).
The output transformer Tr2 is assembled on a core made of Sh19 plates with a thickness of 45 mm. Figure 28 shows a diagram and a variant of the arrangement of its windings. The primary winding 1-6 is wound with PEV-2 wire 0.18 and contains 3000 turns, the secondary winding 7-12 is wound with PEV-2 wire 0.57, 180 turns. The pins are arranged so as to make the jumpers of pins 3-4, 7-9-11, 8-10-12 short. You need to put tubes on the terminals and solder them to the mounting blocks installed on the transformer.

The advantage of A. Baev's low-frequency power amplifier (MRB-1967) is that it is assembled from widely used radio components, its electrical circuit is well developed and, when repeated, can be easily adjusted using one voltammeter. The amplifier develops a maximum output power of 30 or 60 W, depending on how many tubes operate in the output stage (two or four).
Reproducible frequency band 30...18000 Hz; nonlinearity of frequency response no more than 3 dB. The sensitivity in the "Microphone" operating mode is about 5 mV, and in the "Pickup" mode - 150 mV. The amplifier is powered from a 220 V network; power consumption 80-160 W depending on output power.

Figure 29 Tube amplifier circuit by A. Baev

Figure 30 Location of the windings of the output transformer of A. Baev’s tube power amplifier

		WINDING DATA OF A. BAEV'S TUBE AMPLIFIER
Designation on the wire turns diagram			Brand and diameter	Cores
		One layer

DC load resistance, Ohm	Number of turns of the secondary winding
	For 2 lamps	For 4 lamps

Setting up an amplifier mainly consists of checking and setting the operating modes of the radio tubes in accordance with those indicated on the circuit diagram (Fig. 29). After the final installation check, turn on the power and check that the secondary winding of the output transformer is connected correctly. If the amplifier is excited, the secondary winding leads should be swapped. Then, using potentiometer R35, set the voltage (-38 V) on the control grids of the output stage lamps. After this, the operating modes of all other cascades are checked. If they deviate from the norm by more than 10%, it is necessary to check the resistor values ​​and the serviceability of the capacitors. Lastly, potentiometer R42 is used to set the OOS value, guided by the fact that with a very deep connection, it is possible to excite the UMZCH at ultra-low frequencies, and with a low connection, due to the higher gain, an increased background of alternating current appears.

Less powerful, but of higher quality, is the circuit of a portable audio frequency amplifier by B. Morozov (MRB-1965). The described amplifier (Fig. 31) can find the widest application in the radio supply of rural clubs and cultural centers, schools and other audiences.

Figure 31 Circuit diagram of a tube power amplifier by B. Morozov

The rated output power of the amplifier is 35 W, and the maximum is 45. It reproduces a frequency band in the range from 20 Hz to 20 kHz. The frequency response of the amplifier has a roll-off of 3 dB at a frequency of 20 kHz and a rise at a frequency of 20 Hz of +7 dB. The unevenness of the frequency response in the frequency band from 40 Hz to 12 kHz does not exceed +1 dB. Nonlinear distortion at power up to 25 W is practically absent, the noise level at maximum gain and short-circuited input is 48 dB. Under the same conditions and the microphone stage is turned on, the noise level is 40 dB. The amplifier output is 24 V, designed for a load of 18 ohms, 12 V at 4.5 ohms, and 3 V at 0.28 ohms.
Each input of the bass amplifier has its own volume control, which allows you to make combined recordings, for example, recording speech against the background of music. The microphone stage of the amplifier is assembled using a rheostatic-capacitive circuit on the left (according to the circuit) triode of the L1 type 6N9 lamp. The second amplifier stage is assembled on the right triode of a 6N9 lamp; it is a conventional voltage amplifier. Resistance R14 is the ohmic equivalent of the microphone stage. This resistance maintains the specified mode of lamp L1 when the microphone stage is turned off. The filament of lamp L1 is powered by direct current, which significantly reduces the background level of the entire amplifier; when the microphone stage is not working (the amplifier is powered by another signal source), the anode power of the microphone stage lamp should be turned off with switch Bk2. When operating from the “Sv” pickup and the “L” broadcast line, the signal, bypassing the microphone stage, immediately enters the lamp grid of the first voltage amplifier. Resistors R15, R16 and R6, R7 form a voltage divider that allows you to obtain equal signals from the pickup, broadcast line and microphones.
Thanks to such deep negative feedback (20 dB), the frequency and nonlinear distortions introduced by the final and pre-final stages are sharply reduced, and the dependence of the output voltage level on the load resistance is also reduced."
To ensure symmetry of the pre-terminal stage over the entire frequency range, a balancing capacitor C17 is connected in parallel with resistance R38 (390 kOhm). By shunting resistance R32, it compensates for the drop in frequency response at higher audio frequencies. To prevent self-excitation of the amplifier at high frequencies, resistance R32 is included in the grid circuit of the upper (according to the diagram) triode of the 6HB lamp.
The final stage of the amplifier is assembled according to a push-pull circuit using four 6PZ lamps; it operates in class AB1 mode. Each of the 6PZ lamps is loaded onto a separate winding of the output transformer. To combat high-frequency generation, resistances R39, R41, R42, R43, R44, R45, R46, R47 are included in the control and screen grid circuits of each lamp.
The negative bias is supplied from a special rectifier, which makes the operation of the final stage more stable and also reduces the distortion it introduces.
The amplifier is powered by a rectifier assembled using a bridge circuit using 16 D7Zh type diodes. The diodes are shunted with resistances of 100 kΩ, which protect them from breakdown in the event that the resistance of the diodes to the reverse current differs sharply from each other (the resistance of the diodes to the reverse current must be at least 200 kΩ),
Power transformer Tr1 is assembled on a core made of Sh-40 plates, the thickness of the set is 60 mm. All transformer windings are wound on a common getinax frame. The network winding is wound first. It contains 250 turns of PEL 0.93 wire and 190 turns of PEL 0.74 wire. Both sections are connected in series. The second filament winding of 6PZ lamps connected in series is wound onto the mains winding. It contains 50 turns of PEL 0.8 wire with a tap from the 25th turn, which is grounded. This winding simultaneously shields the network winding from others. A step-up winding is wound on top of the filament winding, which consists of 920 turns of PEL 0.35 wire. 13 turns of PEL 0.8 wire are wound onto this winding from one edge to power the filament lamps L2 and LZ, and then, stepping back 3 mm from the filament winding, in the same row a winding is wound in two layers to power the bias rectifier, which contains 160 , turns of PEL wire 0.15. When winding a transformer, wax paper is laid between the rows, and two layers of varnished cloth are placed between the windings.
The choke is made on a Ш26хЗО core by winding 2000 turns of PEL 0.31 wire. For the output transformer, a set of Ш25 plates with a thickness of 60 mm is used. The anode winding consists of four sections of 1350 turns of PEL 0.2 wire. The secondary winding consists of five sections, four contain 80 turns of PEL 0.66 wire and one contains 25 turns of PEL 1.5. First, one section I of the secondary winding is wound in one layer. Two layers of varnished cloth are wound on top of it, then section II of the anode winding is wound in five layers, laying them with a layer of varnished cloth or two layers of thin waxed paper. Two layers of varnished cloth are wound over the primary winding section, then the secondary winding section is wound, then the primary winding again, and so on. The last section will be the fifth section of the secondary winding. The winding order is shown by serial numbers in the diagram.

A high-quality stereo amplifier by I. Stepin (MRB-1967) can work both with a piezoelectric pickup and with a receiver that has a VHF range and a special attachment for receiving stereo transmissions. The amplifier has high gain and high sensitivity. From the pickup input it is at least 100 mV. The amplifier tone control limits are 15-20 dB at lower sound frequencies and 12-16 dB at higher ones. The volume control range for each channel is 40 dB. The amplifier reproduces an audio frequency band from 50 to 13000 Hz with an uneven frequency response of 6 dB.
The imbalance in volume control, timbres and amplifier frequency characteristics for both channels does not exceed 4 dB. The transition attenuation at a frequency of 1000 Hz is about 45 dB, at a frequency of 10000 Hz - 30 dB. Thanks to the use of separate power supply for the final and preliminary amplification stages, the background level at the amplifier output with a rated output power of 10 W (for each channel) and an open input is no worse than 50 dB. Nonlinear distortion coefficient at rated output power is no more than 4%. Power consumption 130 W.

Figure 32 I. Stepin tube amplifier circuit

For stereo playback, two similar high-quality amplifiers are used, which can be combined using the Bk1 switch when playing recordings from monophonic records (Fig. 32).
Winding data of transformers are given in the table.

Designation on the diagram	Number of turns	Wire brand and diameter, mm	Core

A further improvement of the UMZCH circuitry can be considered a high-quality tube amplifier by E. Sergievsky (R-2/90). He believes that the development of digital audio reproduction has again exacerbated the problem of creating a high-quality power amplifier. In search of ways to solve it, many designers turned their attention to tube amplifiers. The reason for this behavior can be understood if we remember that these amplifiers, with relatively more moderate technical characteristics than their transistor counterparts, have a wider dynamic range and provide, from the point of view of connoisseurs of high fidelity sound reproduction, a cleaner, more natural and transparent sound.
The diagram of one channel of a full stereo tube amplifier with a tone control is shown in Fig. 33. It can operate from any (including high-impedance) source of audio signals that provides an output voltage of at least 0.25 V. A distinctive feature of the amplifier is the use of highly symmetrical pre-amplification stages and the use of cross-feedback, stabilizing the operating modes and parameters of the UMZCH.

Figure 33 Schematic diagram of a tube power amplifier by E. Sergievsky

Main technical characteristics: Nominal input voltage 0.25V. Input impedance, 1 MOhm. Nominal (maximum) output power 18 (25) W. The nominal range of reproduced frequencies is 20...20,000 Hz. Harmonic distortion at 1 W output power in the nominal frequency range is 0.05%. Relative noise level (unweighted value) no more than 85 dB. The output voltage slew rate is at least 25 V/µs. The tone control range is -15...+15dB.
The input signal through the stereo balance control R1 and the finely compensated volume control on the elements Cl, C2, SZ, R2-R4 is supplied to the input of the first stage of the UMZCH, assembled on a low-noise pentode 6ZH32P (VL1). In this stage, you can also use a 6S62N nuvistor with better noise characteristics (Fig. 34). It is only important that the voltage gain of this stage be more than 50, which will make it possible to compensate for the signal attenuation at the edges of the reproduced frequency range introduced by the tone control.

Figure 34 Using a Lower Noise Input Stage

Figure 35 Printed circuit board drawing of a tube power amplifier by E. Sergievsky

The phase inversion and pre-terminal stages are covered by cross-feedback, which compensates for the influence of mounting capacitance and improves the phase relationships of inverted signals at higher audio frequencies. The circuits of this connection are formed by capacitors C13-C16. In addition to cross-feedback, the amplifier includes three main feedback circuits. The voltage of the first of them is removed from the secondary winding of the output transformer T1 and through the circuit R34, C 17 is supplied to the input (control grid of the VL2.2 lamp) of the phase inverter, the voltage of the second is removed from the anode loads of the final stage lamps VL5, VL6 and is supplied through the circuits R28C26 and R35C25 to the cathodes of the triodes of the pre-final stage VL4.1 and VL4.2. And finally, the third OOS circuit covers only the final stage along the shielding grids.
The UMZCH is mounted on a printed circuit board made of foiled fiberglass laminate 1.5 mm thick (Fig. 35). For installation, fixed resistors MLT, variable resistors SZ-ZOv-V (Rl, R2, R13, R15), SZ-ZOa (R22) and S5-5 (R42), capacitors K50-12 (S19-S22, S27-S29) were used. , K73-5 (C23-C26), KT (C13-C16) and KM (rest).
The output transformer is made on an armored tape magnetic conductor ШЛ25Х40 (tape thickness 0.1 mm). You can also use a W-shaped magnetic core made of Sh25 plates and a set thickness of 40 mm. Windings 1-2 and 13-14 each contain 50, and 6-7-8-9 - 15+15+15 turns of wire PEV-2 1.0, windings 5-4-3 and 10-11-12 consist of 600 +800 turns of wire PEV-2 0.2.
When winding the output transformer, it is necessary to ensure strict symmetry of the halves of its primary winding by dividing the frame into two identical parts with a partition parallel to the side ones. Before installing the UMZCH, it is necessary to carefully check the correct installation and reliability of the soldering. Then, turning on the power, measure the voltage in the filament circuits of all lamps (they should be within 6.3...6.6 V), on their electrodes and on capacitors C20-C22 and C28, C29 (their permissible deviation from those indicated on principle should not exceed 5%).
Next, setting the tone controls to the middle position and the signal level control to the maximum volume position, apply a sinusoidal signal with a frequency of 1 kHz and a level of 0.1 V to the amplifier input. Then, alternately connecting the oscilloscope to the control grids of the VL5 and VL6 lamps, you need to check the shape of the positive and negative half-waves of the signal with a smooth increase in voltage at the amplifier input (until saturation). Having completed this operation, the tuning resistor R22 needs to achieve complete symmetry and equality of the amplitudes of the controlled signals on the grids of the output lamps with an accuracy of 0.05 V.
After this, by connecting the equivalent load in the form of a constant resistor with a resistance of 16 Ohms and a power of 20 W to the secondary winding of transformer T1 and setting the voltage at the amplifier input to 0.25 V, you should check the alternating voltages on the electrodes of all lamps for compliance with those indicated on the circuit diagram.
Next, by monitoring the voltage at the load resistance equivalent, using its maximum value, experimentally find the location of the output of the secondary winding of the transformer to which the R34-C17 OOS circuit should be connected. Then, by measuring the nominal (with an input signal of 0.25 V) and maximum (with barely noticeable saturation) voltage at the load resistance equivalent, use the well-known formula to determine the nominal and maximum power of the amplifier.
The circuit diagram shows an option for connecting a load with a resistance of 16 Ohms. To operate an amplifier with an AC resistance of 8 ohms, when adjusting the amplifier, you should connect the corresponding load equivalent to it and, using the method outlined above, select a new tap location for the secondary winding of the output transformer.

Again, a design by an author already known from this book. This is a powerful two-channel UMZCH A. Baev (MRB-1974). This design cannot be classified as multi-channel, because both channels are identical and can be used simultaneously in the “dual mono” mode (analogous to “stereo” for signals with a large stereo base or “quasi-stereo” for large rooms or areas) or “quad” if there are two sets amplifier
The amplifier has the following data: maximum power per channel 65 W, channel load resistance 14 Ohms, frequency band 20...40000 Hz with nonlinear distortion coefficient 0.6...0.8%, sensitivity from the microphone input.5... 0.6 mV, from input 3-20 mV, from input 4 0.8 V. Separate tone control at frequencies of 40 Hz and 15 kHz within 15 dB.

Figure 36 Schematic diagram of A. Baev’s power amplifier

The schematic diagram of one channel is shown in Fig. 36. Microphone amplifiers are assembled using transistors T1 - T4. To obtain a good signal-to-noise ratio and high input impedance, their first stages are assembled using field-effect transistors. The cascades are covered by negative current feedback (through resistors R3 and R13), due to which they have a high input impedance over the entire operating frequency range. To reduce the output resistance of the first stages, the source current is chosen to be quite large - about 0.8 mA. Despite this, the noise level at their outputs is very low, since the noise of field-effect transistors does not depend on the current in the channel.
From the drains of transistors T1 and T3, the signals are supplied through separating capacitors C2 and C6 to the second stages of amplifiers assembled on transistors T2 and T4. Resistors R4, R6, R14 and R16 are feedback elements, and resistors R4 and R14, in addition, serve to select and stabilize the operating mode of the transistors.
Variable resistors R7 and R17 are used to adjust the volume of signals supplied to microphone amplifiers.
To eliminate the background of alternating current, the filaments of lamps L1 and L2 are powered by direct current supplied from a rectifier assembled on diodes D17, D18 (Fig. 37). For the same purpose, into the filament circuit of the LZ lamp from the divider R55. R56 is supplied with a positive (relative to the cathode) voltage of 50 V.

Figure 37 Schematic diagram of the power supply for a tube power amplifier by A. Baev

Figure 38 Design of the output transformer of A. Baev’s power amplifier

The review of single-channel push-pull amplifiers is completed by K. Weisbein's stereophonic bridge UMZCH circuit (RAZ/99), recently published in the journal "Radyumator". The author believes that the output transformer is the most critical component of any high-quality audio amplifier and is responsible for many types of distortion. The output stage of the proposed amplifier is built according to the circuit of a series-parallel push-pull amplifier (PPP-Push-Pull-Parallel), proposed by the German engineer Futterman in 1953. The cascade is a bridge, two arms of which are formed by the internal resistances of the output lamps, and the other two by the source resistances anode supply.
The direct components of the anode currents of the lamps flow through the load in antiphase, so there is no constant magnetization of the output transformer, as in a conventional push-pull amplifier. The alternating components of the anode currents of the output lamps flow through the load in phase, since antiphase voltages are applied to the lamp grids.
If in a conventional push-pull amplifier the AC output lamps are connected in series, then in a counter-parallel amplifier they are connected in parallel. Therefore, the optimal load resistance for a counter-parallel amplifier is 4 times less than for a conventional push-pull amplifier. This means that the inductance of the primary winding of the output transformer in a counter-parallel amplifier with the same nonlinear distortions at a given low frequency will be 4 times less than in a conventional one. The design of the output transformer is greatly simplified. In an anti-parallel amplifier, the output transformer can be replaced with a kind of autotransformer with a midpoint, which will lead to a reduction in distortion at higher frequencies due to leakage inductance and distributed capacitances between the windings of the output transformer. The circuit diagram of the amplifier is shown in Fig. 39.

Figure 39 Circuit diagram of a tube power amplifier by K. Weisbein

The technical characteristics of the UMZCH are as follows. Output power with nonlinear distortion less than 1% 20 W. Input sensitivity 250 mV. Power amplifier sensitivity 0.5 V. Reproducible frequency band 10-70,000 Hz. Load resistance 2, 4, 8, 16 Ohms. The tone control range is 10 dB.
The first stage of the amplifier is made on half of a 6N23P lamp (6N1P, 6N2P, 6N4P), the second stage is a conventional resistive amplifier. A wide-range tone control is included between the first and second stages. The P2K switch was used as a potentiometer.
The use of a phase reflex cascade assembled according to a cathode-coupled circuit (VL3) ensures high symmetry of output voltages over a wide frequency range and low nonlinear distortions. With the previous stage (VL2), which is a cathode follower, the bass reflex stage is galvanically coupled to reduce phase shift at low frequencies, which improves the stability of the amplifier.
The output stage is assembled according to the PPP circuit using 6P41S lamps, which have sufficient power and low internal resistance (12 kOhm). Instead of 6P41S, you can use 6PZS, 6P27S, EL34 lamps. The amplifier is covered by negative feedback, the voltage of which is supplied through a resistor from the output winding of the autotransformer to the cathode circuit of the first stage of the power amplifier.
The amplifier is powered by two identical half-wave rectifiers using D237B diodes. The power transformer has 4 anode voltage windings of 240 V each. It is noteworthy that the capacitors in the power supply are not connected to the case.
The power transformer is wound on a toroidal core. It is better if each channel of the stereo amplifier has a separate power transformer. The amplifier provides separate switching of the filament and anode voltages, which allows you to increase the life of the output lamps.
The amplifier is mounted on a metal chassis using the hinged mounting method using circuit boards, as well as lamp panel blades, which reduces interference and mounting capacity.
Installation comes down to checking the correct installation. The voltage difference between the cathode of the cathode follower and the cathodes of the bass reflex lamp should be 2 V. With a correctly assembled amplifier, the voltage between terminals 10 and 13 of the output transformer should be zero. If hum occurs, it is necessary to rephase one of the anode windings of the power transformer.

Figure 40 Location of the windings of the output transformer of the amplifier K. Weisbein

The design of the output transformer (Fig. 40) should be discussed in more detail. The transformer is wound with PEV-2 wire on a toroidal magnetic conductor assembled from a steel tape 0.35 mm thick and 50 mm wide. The outer diameter of the torus is 80 mm, the inner diameter is 50 mm. Steel grade EZZO. The winding is divided into sections to reduce leakage inductance and achieve high symmetry of the two halves of the winding. The winding data of the transformer are given in the table. The output transformer can also be made on an W-shaped core with a cross-section of 7-8 cm, the windings of which are divided into sections. The sections are connected to each other in series.

		Wire diameter, mm	Number of turns
	5-6-7-8-9 (BRANDS EVERY 30 TURNS)

— most connoisseurs of high-quality music, who know how to handle soldering equipment and have some experience in repairing radio equipment, can try to assemble a high-class tube amplifier, which is usually called Hi-End, on their own. Tube devices of this type belong in all respects to a special class of household radio-electronic equipment. Basically, they have an attractive design, with nothing covered by a casing - everything is in plain sight.

After all, it is clear that the more visible the electronic components installed on the chassis are, the greater the authority of the device. Naturally, the parametric values ​​of a tube amplifier are significantly superior to models made with integrated or transistor elements. In addition to this, when analyzing the sound of a tube device, all attention is paid to the personal assessment of the sound rather than to the image on the oscilloscope screen. In addition, it has a small number of used parts.

How to choose a tube amplifier circuit

If there are no particular problems when choosing a pre-amplifier circuit, then when choosing a suitable final stage circuit, difficulties may arise. Tube audio power amplifier may have several versions. For example, there are single-cycle and push-pull devices, and also have different operating modes of the output path, in particular “A” or “AB”. The output stage of single-ended amplification is, by and large, a sample, because it is in mode “A”.

This operating mode is characterized by the lowest nonlinear distortion values, but its efficiency is not high. Also, the output power of such a stage is not very large. Therefore, if it is necessary to sound an internal space of medium size, a push-pull amplifier with the “AB” operating mode will be required. But when a single-cycle device can be made with only two stages, one of which is preliminary and the other amplifying, then a driver is needed for the push-pull circuit and its correct operation

But if single-cycle tube audio power amplifier may consist of only two stages - a pre-amplifier and a power amplifier, then a push-pull circuit for normal operation requires a driver or cascade that forms two voltages of identical amplitude, shifted in phase by 180. Output stages, regardless of whether it is single-ended or push-pull, require the presence of output transformer. Which acts as a matching device for the interelectrode resistance of a radio tube with low acoustic resistance.

True admirers of “tube” sound argue that the amplifier circuit should not have any semiconductor devices. Therefore, the power supply rectifier must be implemented using a vacuum diode, which is specially designed for high-voltage rectifiers. If you intend to repeat a working, proven tube amplifier circuit, then you do not need to immediately assemble a complicated push-pull device. To provide sound in a small room and obtain an ideal sound picture, a single-ended tube amplifier is fully sufficient. In addition, it is easier to manufacture and configure.

The principle of assembly of tube amplifiers

There are certain rules for installing radio-electronic structures, in our case these are tube audio power amplifier. Therefore, before starting the manufacture of the device, it would be advisable to thoroughly study the primary principles of assembling such systems. The main rule when assembling structures using vacuum tubes is to route the connecting conductors along the shortest possible path. The most effective method is to refrain from using wires in places where you can do without them. Fixed resistors and capacitors must be installed directly on the lamp panels. In this case, special “petals” must be used as auxiliary points. This method of assembling a radio-electronic device is called “mounted mounting”.

In practice, printed circuit boards are not used when creating tube amplifiers. Also, one of the rules says - avoid laying conductors parallel to each other. However, such a seemingly chaotic layout is considered the norm and is completely justified. In many cases, when the amplifier is already assembled, a low-frequency hum is heard in the speakers; it must be removed. The primary task is performed by the correct choice of the ground point. There are two ways to organize grounding:

• The connection of all wires going to the “ground” at one point is called an “asterisk”
• Install an energy-efficient electrical copper bus around the perimeter of the board, and solder conductors to it.

The location for the grounding point must be verified by experiment, listening for the presence of background. To determine where the low-frequency hum comes from, you need to do this: Using a sequential experiment, starting with the double triode of the pre-amplifier, you need to short-circuit the lamp grids to ground. If the background decreases noticeably, it will become clear which lamp circuit is causing the background noise. And then, also experimentally, you need to try to eliminate this problem. There are auxiliary methods that are required to be used:

Pre-stage tubes

• Electrovacuum lamps of the preliminary stage must be covered with caps, and they, in turn, must be grounded
• Housings of trimming resistors are also subject to grounding
• Lamp filament wires need to be twisted

Tube audio power amplifier, or rather, the filament circuit of the pre-amplifier lamp can be powered with direct current. But in this case, you will have to add another rectifier assembled using diodes to the power supply. And the use of rectifier diodes in itself is undesirable, since it breaks the design principle of manufacturing a Hi-End tube amplifier without the use of semiconductors.

The paired placement of the output and mains transformers in a lamp device is quite an important point. These components must be installed strictly vertically, thereby reducing the background level from the network. One of the effective ways to install transformers is to place them in a casing made of metal and grounded. The magnetic cores of transformers also need to be grounded.

Retro components

Radio tubes are devices from ancient times, but they have become fashionable again. Therefore it is necessary to complete tube audio power amplifier with the same retro elements that were installed in the original lamp designs. If this concerns permanent resistors, then you can use carbon resistors that have high stability of parameters or wire resistors. However, these elements have a large scatter - up to 10%. Therefore, for a tube amplifier, the best choice would be to use small-sized precision resistors with a metal-dielectric conductive layer - C2-14 or C2-29. But the price of such elements is significantly high, so instead of them, MLTs are quite suitable.

Particularly zealous adherents of the retro style obtain an “audiophile’s dream” for their projects. These are carbon resistors BC, developed in the Soviet Union specifically for use in tube amplifiers. If desired, they can be found in tube radios from the 50s and 60s. If according to the circuit the resistor must have a power of more than 5 W, then PEV wire resistors coated with glassy heat-resistant enamel are suitable.

Capacitors used in tube amplifiers are generally not critical to a particular dielectric, as well as to the design of the element itself. Any type of capacitor can be used in the tone control paths. Also, in the rectifier circuits of the power supply, you can install any type of capacitors as a filter. When designing high-quality low-frequency amplifiers, the coupling capacitors installed in the circuit are of great importance.

They have a special influence on the reproduction of a natural, undistorted sound signal. Actually, thanks to them we get exceptional “tube sound”. When choosing coupling capacitors that will be installed in tube audio power amplifier, special attention must be paid to ensure that the leakage current is as small as possible. Because the correct operation of the lamp, in particular its operating point, directly depends on this parameter.

In addition, we must not forget that the separating capacitor is connected to the anode circuit of the lamp, which means that it is under high voltage. So, such capacitors must have an operating voltage of at least 400v. One of the best capacitors working as a transition capacitor are those from JENSEN. It is these capacities that are used in top-end HI-END class amplifiers. But their price is very high, reaching up to 7,500 rubles for one capacitor. If you use domestic components, then the most suitable ones would be, for example: K73-16 or K40U-9, but in terms of quality they are significantly inferior to branded ones.

Single-ended tube audio power amplifier

The presented tube amplifier circuit consists of three separate modules:

• Pre-amplifier with tone control
• The output stage, that is, the power amplifier itself
• Power supply

The preamplifier is manufactured using a simple circuit with the ability to adjust the signal gain. It also has a pair of separate tone controls for low and high frequencies. To increase the efficiency of the device, you can add an equalizer for several bands to the design of the preamplifier.

Electronic components of the preamplifier

The pre-amplifier circuit presented here is made on one half of a 6N3P double triode. Structurally, the preamplifier can be manufactured on a common frame with an output stage. In the case of a stereo version, two identical channels are naturally formed, therefore, the triode will be fully involved. Practice shows that when starting to create any design, it is best to first use a circuit board. And after setting it up, assemble it in the main building. Provided that it is assembled correctly, the preamplifier begins to operate synchronously with the supply voltage without any problems. However, at the setup stage you need to set the anode voltage of the radio tube.

The capacitor in the output circuit C7 can be used K73-16 with a rated voltage of 400v, but preferably from JENSEN, which will provide better sound quality. Tube audio power amplifier not particularly critical of electrolytic capacitors, so any type can be used, but with a voltage margin. At the setup stage, we connect a low-frequency generator to the input circuit of the pre-amplifier and apply a signal. An oscilloscope must be connected to the output.

Initially, we set the input signal range to within 10 mv. Then we determine the output voltage value and calculate the amplification factor. Using an audio signal in the range of 20 Hz - 20000 Hz at the input, you can calculate the throughput of the amplification path and display its frequency response. By selecting the capacitance value of the capacitors, it is possible to determine the acceptable proportion of high and low frequencies.

Setting up a tube amplifier

Tube audio power amplifier implemented on two octal radio tubes. A double triode with separate cathodes 6N9S connected in a parallel circuit is installed in the input circuit, and the final stage is made on a fairly powerful output beam tetrode 6P13S connected as a triode. Actually, it is the triode installed in the final path that creates exceptional sound quality.

To perform a simple adjustment of the amplifier, an ordinary multimeter will be enough, but to make precise and correct adjustments you need to have an oscilloscope and an audio frequency generator. You need to start by setting the voltage at the cathodes of the 6N9S double triode, which should be within 1.3v - 1.5v. This voltage is set by selecting a constant resistor R3. The current at the output of the 6P13S beam tetrode should be in the range from 60 to 65 mA. If a powerful constant resistor 500 Ohm - 4 W (R8) is not available, then it can be assembled from a pair of two-watt MLTs with a nominal value of 1 kOhm and connected in parallel. All other resistors indicated in the diagram can be installed of any type, but preference is still given to C2-14.

Just like in the preamplifier, the important component is the decoupling capacitor C3. As mentioned above, the ideal option would be to install this element from JENSEN. Again, if you don’t have them at hand, you can also use Soviet film capacitors K73-16 or K40U-9, although they are worse than overseas ones. For correct operation of the circuit, these components are selected with the lowest leakage current. If it is impossible to carry out such a selection, it is still advisable to buy elements from foreign manufacturers.

Amplifier power supply

The power supply is assembled using a 5Ts3S direct-heated kenotron, which provides AC rectification that fully complies with the design standards for HI-END class tube power amplifiers. If it is not possible to purchase such a kenotron, then you can install two rectifier diodes instead.

The power supply installed in the amplifier does not require any adjustment - everything is turned on. The topology of the circuit makes it possible to use any chokes with an inductance of at least 5 H. As an option: using such devices from outdated TVs. The power transformer can also be borrowed from old Soviet-made lamp equipment. If you have the skills, you can make it yourself. The transformer must consist of two windings with a voltage of 6.3v each, providing power to the amplifier radio tubes. Another winding should have an operating voltage of 5v, which is supplied to the kenotron filament circuit and the secondary one, which has a midpoint. This winding guarantees two voltages of 300v and a current of 200 mA.

Power amplifier assembly sequence

The procedure for assembling a tube audio amplifier is as follows: first, the power supply and the power amplifier itself are made. After the settings have been made and the necessary parameters have been installed, the preamplifier is connected. All parametric measurements with measuring instruments should be done not on a “live” acoustic system, but on its equivalent. This is in order to avoid the possibility of expensive acoustics being decommissioned. The load equivalent can be made of powerful resistors or thick nichrome wire.

Next you need to work on the housing for the tube audio amplifier. You can develop the design yourself, or borrow it from someone. The most affordable material for making the body is multilayer plywood. The output and preliminary stage lamps and transformers are installed on the upper part of the housing. On the front panel there are tone and sound control devices and a power supply indicator. You may end up with devices like the models shown here.

Many music lovers prefer to listen to their favorite tunes using tube amplifiers. What are the specifics of these devices? Based on what criteria can you choose the optimal model of the corresponding device?

What is interesting about tube

An amplifier is one of the key components of the acoustic infrastructure, which is responsible for increasing the power of the signals coming from sound sources, switching the corresponding devices, adjusting the volume level, and also transmitting the signal, the power of which is amplified, to audio equipment designed to play tunes.

Tube amplifiers use radio tubes as a key element of circuitry. They perform the function of reinforcing elements. Typically, tube amplifiers provide less distortion. As many music lovers note, the corresponding devices are characterized by warmer, softer playback of melodies - especially when playing mid-range and high frequencies.

Another major advantage of a tube amplifier is that in many cases it provides a richer sound compared, for example, with transistor devices. This is possible thanks to the unique properties of the lamps themselves, which, for example, are adapted to function without auxiliary correction, which is necessary to maintain the operation of semiconductor devices.

Single-cycle and push-pull devices

Lamp devices are most often classified into 2 main categories - class A and class AB. The former are also called single-cycle. In them, amplifying elements stimulate an increase in the power of both half-waves in the signal - both positive and negative. The second devices are also called push-pull. In them, each subsequent cascade of increasing power involves the use of different elements - one can be responsible for the positive half-wave, while the other can be responsible for the negative. Class AB amplifiers are usually more economical and efficient, and often more powerful. But discussions sometimes arise on this issue among music lovers.

The devices under consideration in many cases are much more expensive than their transistor counterparts, despite the fact that their design is quite simple. Many music lovers assemble the corresponding devices on their own - however, you need to try to find the best tube amplifier circuits - on 6P3S, for example, or other popular tubes. For connoisseurs of music played using the devices in question, their price often becomes secondary - if the decision is made not to build an amplifier, but to buy it. At the same time, the characteristics, of course, play an undeniably significant role when choosing a device. Let's look at what they can be, as well as examples of popular models of the corresponding type of device.

Amplifier ProLogue EL34: characteristics and reviews

According to many experts, the best tube amplifier, or at least one of the leaders in the relevant criterion (from those that belong to the budget segment), is the ProLogue Classic EL34 device. This device can operate using two types of lamps - the actual EL34 or KT88. In this case, the user does not have to reconfigure the amplifier.

According to experts - reviews reflecting their opinions can be found on many thematic portals - one of the main advantages of the device is that it is equipped with interfaces that allow the load to be applied to the lamp smoothly, which helps to increase its service life. The amplifier is equipped with an efficient device. It has quite a large power, which is 35 W.

Triode Amplifiers

Another amplifier that belongs to the budget category is the TRV-35 device, produced by the Japanese brand Triode. The fact that it is assembled in Japan largely determines the quality of the corresponding product. The amplifier is versatile - perhaps the best tube amplifier in its segment from this point of view. The lamps that can be used on the device are EL34; in some cases, it is possible to use ElectroHarmonix elements manufactured in Russia.

According to experts, among the most notable options of the amplifier in question is the ability to connect to modern home theaters.

Another well-known product of the Japanese brand Triode is the TRX-P6L device. As some experts note, this device is the best tube amplifier in the Triode line in terms of functionality. Thus, it contains, in particular, a four-band equalizer, which is designed to optimize the timbre of the melody, taking into account the specific acoustic environment in the room, as well as the parameters of the sound systems used. The device in question allows you to use different categories of lamps - EL34, also KT88. The device is equipped with a reverse interaction depth regulator. The amplifier can operate in 2 modes - triode and ultralinear.

Another notable device produced under the Triode brand is the VP-300BD amplifier. Many music lovers ask a common question: “Single-cycle or push-pull tube amplifier - which is better?” They can, by choosing the VP-300BD, which belongs to the devices of the first type, remain very satisfied with the purchased device. The device in question is a triode, classified as an open type amplifier. It can be noted that the output stage of the device operates on 300B triodes, which are classified as direct channel.

Audio Research VSi60

Among the most famous brands producing tube amplifiers is the American corporation Audio Research. Its most technologically advanced products include the VSi60 device. Many music lovers are convinced that tube amplifiers are better than transistor ones, and the device produced by an American company makes it possible to put forward a strong argument in favor of devices of the first type: according to experts, the amplifier in question provides the most impressive sound scale, quite comparable to the performance of transistor devices. The main lamps that the American device works with are KT120. Volume control for the one in question

Amplifiers Unison Research

Another well-known brand manufacturer of the devices in question is Unison Research. The most effective solutions developed by this corporation include the S6 amplifier. It is arguably the best tube amplifier, or at least one of the leading solutions, in terms of its combination of characteristics typical of a Class A device: high power of 35 W, as well as a significant damping factor. The device uses 2 direct-channel triodes located in each channel.

As experts note, the amplifier in question is characterized by the highest sound quality in terms of detail and purity of the reproduced melody.

The next well-known product produced under the Unison Research brand is the P70 amplifier. In turn, it is two-stroke. Music lovers who wonder why a single-ended tube amplifier plays better than a push-pull amplifier somewhat change their perception of the effectiveness of the corresponding devices after listening to music while using the device in question. The developers of the P70 amplifier managed to provide exceptionally high sound quality with a very impressive device power - more than 70 W.

As experts note, the device can connect to an acoustic infrastructure that forms a fairly impressive load. The device in question is also characterized by genre versatility. If we consider the best tube amplifiers for listening to rock music, the P70 device can rightfully be classified as a leading solution.

Among the well-known single-cycle products manufactured under the Unison Research brand is the Preludio device. It also operates in Class A. It uses powerful KT88 tetrodes. The power of the device is 14 W. Therefore, the amplifier requires connection to an acoustic infrastructure that has a sufficiently high level of sensitivity.

McIntosh

Another well-known brand that produces amplifiers is the American corporation McIntosh. Many music lovers, wondering which tube amplifier is better, first of all associate the highest quality products with those devices that are manufactured under the McIntosh brand. This corporation is one of the world's most recognizable manufacturers of audio equipment in the Hi-End segment.

It may be noted that the MC275 product from McIntosh first appeared on the market in 1961. Since then, it has undergone a number of improvements, but is still produced under the historical name. In principle, this amplifier is one of the legendary devices, one of the best products in the world in the Hi-End segment. The device uses KT88 lamps. The amplifier power is 75 W in stereo playback mode.

Audio Note

Another well-known brand in the amplifier market is Audio Note. Among its most popular products is Meishu Phono. Perhaps this is the best tube amplifier in its segment, if we consider the corresponding devices from the point of view of maintaining the purity of technology. So, it does not involve a single semiconductor. The structure of the device’s power supply contains 3 transformers, 3 kenotrons, and 2 chokes. The output stage uses 300B triodes. The amplifier design includes an effective tube phono preamplifier. The device in question has a rather modest power, which is 9 watts. Nevertheless, the device is compatible with many modern types of floor-standing acoustic equipment.

Determining the best tube sound amplifier based on the subjective perception of its operation is quite difficult. However, you can get closer to solving such a problem by comparing certain device models according to their main characteristics, as well as analyzing the relevant parameters.

Choosing the best amplifier: model comparison parameters

What parameters can be considered as key? According to modern experts, the most important characteristics in this case may be:

Harmonic distortion level;

Signal to noise ratio;

Support for communication standards;

Energy consumption level.

In turn, these parameters can be compared with the price of the device.

Choosing an amplifier: power

As for the first indicator - power, it can be presented in the widest range of values. Optimal for solving most problems that characterize the use of a tube amplifier is an indicator of about 35 W. But many music lovers welcome an increase in this value - for example, up to 50 W.

At the same time, many modern high-tech devices of the corresponding type work excellently at a power of about 12 W. Of course, in many cases they require connection to a high-performance acoustic infrastructure. But the use of effective audio equipment is one of the mandatory attributes of using, in fact, the devices in question. Why a tube amplifier is better than more modern modifications of devices is a question that is not particularly relevant for many music lovers, since they have repeatedly been convinced in practice of the objective superiority of the corresponding devices in key parameters. And therefore, they try to carry out testing and practical use of tube amplifiers on pre-prepared equipment that meets the highest requirements.

Frequency

Regarding the frequency response of the amplifier, it is highly desirable that it be in the range from 20 to 20 thousand Hz. Although, it should be noted that it is quite rare that modern manufacturers of the devices in question supply amplifiers to the markets that do not meet this criterion. It is difficult to find equipment in the Hi-End segment that does not reach the specified frequency parameters. One way or another, when purchasing a tube amplifier, for example, from a little-known brand, it makes sense to check the frequency range in which it supports.

Harmonic distortion

As for harmonic distortion, it is desirable that it does not exceed 0.6%. Actually, the lower this indicator, the better the sound. The best tube amplifier in a given segment is often determined primarily by harmonic distortion. It’s worth noting right away that the corresponding indicator is not the most significant from the point of view of ensuring good sound quality. However, this parameter characterizes the response of the acoustic infrastructure to the input signal. It is quite difficult in practice to stimulate the response of acoustics during measurements in the same way as is done when playing real signals. But modern tube amplifier brands are trying to ensure the lowest harmonic distortion. Prestigious device models are capable of providing it at a level not exceeding 0.1%. Of course, their cost may be incomparably higher than competing models that have a higher harmonic distortion rate, but for a music lover, the issue of price in this case may be of secondary importance.

Signal to noise ratio

The next parameter is the signal-to-noise ratio; in modern tube amplifiers it most often corresponds to 90 dB or more. In general, this value can be considered very common when comparing the characteristics of various devices, even if presented in different segments. Therefore, if the task is to choose a good single-ended tube amplifier or, for example, a push-pull amplifier, then the parameter under consideration will not always objectively reflect the competitiveness of a particular device. One way or another, the higher the corresponding indicator, the better. It is desirable that it be at least 70. Some top amplifier models provide a signal to noise ratio of more than 100 dB. But their price, as in the case of harmonic distortion, can be impressive.

Other parameters

The remaining parameters - support for certain communication standards, power consumption - are significant, but secondary. It makes sense to pay attention to them, all other things being equal, according to the indicators that we discussed above. One way or another, for a modern amplifier, it can be considered typical to have support for a sufficient number of stereo pairs - about 4, audio outputs for recording sound. Regarding power consumption, the optimal figure is about 280 W.

Of course, when considering the question of which tube amplifier is better, many subjective factors also play a role. Most often, music lovers evaluate the corresponding devices based on their design, build quality, sound level, and ergonomics.

All of the above parameters can be compared with the price of the device, which can be presented in a very wide range of values. But a person for whom the question of why a tube amplifier is better than a transistor one is not particularly relevant, since he knows the answer to it, the price, as we noted above, cannot always be considered as the most significant criterion when choosing a device for listening to his favorite tunes.