Many people, and especially musicians, are familiar with phrases such as “warm tube sound”, “tube sound”. It is clear that tube amplifiers have this sound. Let's look at tube guitar amplifiers together. Let's look at different manufacturers and their models, and also listen to examples. Those who are not familiar with tube amplifiers will learn this topic in detail, and more experienced musicians will hopefully find interesting information for themselves.

The structure of guitar tube amplifiers

To begin with, let me remind you that a guitar amplifier consists of the following parts: a preamplifier (or preamp), a power amplifier and a cabinet (the speaker for sound reproduction and its housing). In classic guitar combo amplifiers, the preamp and the amplifier itself are assembled using tubes. The most common lamps are the 12AX7 model.

12AX7 lamp

And this is what a guitar combo amplifier looks like, assembled using tubes from the inside. Actually, four lamps can be seen with the naked eye. This example is from 1956 Fender.

For those interested in amateur radio, I will give an example of one of the circuits of a tube guitar amplifier.

Fender Guitar Amplifier Circuit

Since the first guitar amplifiers were tube amplifiers, they are considered to be the standard. Models produced in the 50s or 60s of the twentieth century are a great rarity, and are also highly valued by serious musicians and, if sold, sell for very large sums of money. In general, probably every guitarist dreams of owning a tube amp. Modern devices from famous brands also try to make them similar to the old, standard ones. Lamps are used in the design, but modern technologies are also used. The names of such models most often contain the names of their predecessors as a tribute to memory, as well as for more successful marketing.

Legendary tube amplifiers for electric guitar

Fender was one of the first to produce guitar amplifiers. This was in the late 40s of the twentieth century. All amplifiers of that time were tube amplifiers. And in general, electronics were based on tubes. One of the legendary Fender amps was the Bassman model. Initially, this amplifier was created for bass guitars, but the musicians experimented with the sound and it turned out that the Fender Bassman is perfect for electric guitars.

Fender Bassman

You can also note such companies as Marshall and Vox, which began their journey in the mid-twentieth century. Their Marshall JTM45 and VOX AC30 models can rightfully be called legendary.

Marshall JTM45

1966 Marshall JTM45 amplifier

The VOX AC30 was released in 1959.

VOX AC30

1964 VOX AC30 combo amp

You can also give an example of the legendary Hiwatt DR103 amplifier, which was played by the famous David Gilmour from the band Pink Floyd.

Hiwatt DR103

So, sound examples different manufacturers and we heard models. Now we need to move on to listing the pros and cons that are common to most guitar tube amplifiers.

Pros of tube guitar amps:

• Dynamics, pronounced attack;
• Volumetricity of sound;
• Volume and sensitivity have a wide range;
• The beauty of overdriven sound.

Cons of tube guitar amps:

• Large dimensions and considerable weight;
• Fragility of lamps (it is necessary to change them quite often);
• There is a “microphone effect”;
• They achieve their immediate high-quality sound at high volume;
• Amplifiers get hot and often require additional cooling.

By the way, as I mentioned above, there are many modern tube combo amplifiers that represent an excellent combination of new technologies in electronics and the design basis of classic tube models.

How to make a low-power lamp comb from old parts. Single-ended output stage

I made this small low-power tube guitar amp a long time ago, probably about 15 years ago. This was my first design assembled on vacuum tubes Oh. Since at that time I was not involved in lamp technology, I did not have stocks of more or less high-quality components for such a design. And in general, for me it was an experiment. The housing for this small-sized combo amplifier was made by my friend, carpenter and guitar maker Oleg Gnilitsky. Electronic components were literally found "in the dump" and in my electronic junk. I unscrewed the output transformer from some old tube TV, and the lamp sockets were also from some old tube equipment. I used the power transformer type TAN 16-220-50. This excellent transformer happened to be available in my "electronic supplies". After rummaging through my cabinets and drawers for an hour, I scraped to the surface of this world several old lamps of type 6N2P and 6P14P of unknown origin. I speculated that some of these Soviet-made lamps might still be in working order. And so it turned out. And by the way, we must give them credit, these lamps still work in the combi.

This low-power amp was used for several years for home rehearsals and then, when other equipment appeared, it was pushed into the far corner of the electronic junk warehouse and undeservedly forgotten. Recently I was clearing out this electronic trash and found this miracle device. I cleaned it of dust, turned it on and it turned out that it works great to this day. I just had to clean and lubricate the rustling and creaking potentiometers and the small amp was like new again. So I decided to publish this article on my website. I think it will be useful to those who are starting to study tube technology and want to make a cheap small tube amplifier.

Looking ahead, I will say that instead of 6N2P and 6P14P in this combo you can use the more common 12AX7 and EL84 lamps today. The EL84 output lamp is a complete analogue of the 6P14P, and when using a 12AX7, you need to change the connection diagram of its filament circuits, which will be discussed in this article.

Pinout of lamps EL84 and 6P14P

Lamp pinout 6N2P

Lamp pinout 12AX7

The filament circuit of the 6N2P double triode is designed for a voltage of 6.3 volts. The filament voltage must be supplied to lamp legs 4 and 5. The 12AX7 lamp heater is also connected to legs 4 and 5, but is designed for a voltage of 12.6 V. However, the filament circuit of the 12AX7 lamp can also be powered from a voltage of 6.3 V since the connection point of the lamp halves heaters is connected to leg 9. Since each of the lamp halves heaters 12.6 V is designed for the same 6.3 V, we can connect them in parallel and use this lamp instead of 6N2P. To do this, legs 4 and 5 of the 12AX7 lamp must be connected together, and the filament voltage must be applied to pin 9 and to legs 4 and 5 connected together.

Schematic diagram small-sized tube guitar amp. Click on the diagram to enlarge it

The guitar is connected to jack J1. At the amplifier input, the level control on potentiometer R1 is turned on. From the potentiometer slide, through resistor R2, the signal is supplied to the grid of the first triode of the lamp VL1. Resistor R2 serves to prevent the lamp from operating with an unconnected grid in the event of an open circuit in the R1 potentiometer motor circuit (malfunctions in potentiometers occur frequently).

From the output of the cascade (anode of triode VL1-a) amplified signal goes to a three-band tone control, which provides adjustment for high, mid and low frequencies. From the output of the tone control (potentiometer R6) the signal is fed to the “Master” level control. A slight loudness compensation of this regulator is achieved by connecting a capacitor with a capacity of 680 picofarads between the engine and the top terminal of the potentiometer in the circuit. As a result, as the volume decreases, the proportion of high frequencies in the output signal slightly increases. Next, the signal goes to the second voltage amplification stage, assembled on the second half of the lamp - triode VL1-b. From the anode of this triode, through the coupling capacitor C9, the signal is supplied to the output stage of the amplifier.

The output stage is assembled using a single-cycle circuit using two 6P14P (EL84) lamps VL2 and VL3, connected in parallel. Connecting two lamps in parallel allows you to slightly increase the output power of the amplifier. You can use only one lamp, leaving the second socket empty. This is exactly how I use the combo, since at home its output power and sound volume are more than enough for me. With one lamp output power amplifier - 2..3 watts. If you install a second lamp, the power will be around 5 watts. Due to the fact that the tube output stage has a signal clipping characteristic that differs from transistor circuits, we can (subjectively) say that three watts of “tube” is much louder than “transistor” three watts. Although this statement sounds unscientific at first glance, in reality it all comes down to the nature of the distortions introduced by tube circuits into the signal when overloaded. The distortion of a tube circuit is not as sharp as in a transistor one, and therefore a tube amplifier can operate in the saturation region, producing a rather pleasant sound, while transistor circuits, when overloaded, limit the signal very sharply, immediately turning it into a kind of rectangular pulses, which causes a very unpleasant sound. distortions. For this reason, a transistor amplifier must have a much larger gain headroom than a tube amplifier. As we see, there is no mysticism here and everything fits into the laws of physics.

The speaker of the amp has a coil resistance of 8 ohms. It is connected via an output transformer. The output transformer is a very important and most expensive part of a tube amplifier. The sound of such an amplifier and its frequency range greatly depend on the quality and design of the output transformer. Tube amplifiers designed for listening to music often use expensive and difficult to wind ultra-linear transformers. Because a guitar amp does not need as wide a frequency range as an amp designed for listening to music, a guitar amp does not have the same high requirements to the output transformer. You could even say that too wide a frequency range is even harmful for a guitar amplifier. A large amount of high frequencies leads to the appearance of "sand" in the guitar sound. Therefore, loudspeakers intended for use in guitar amps are made with an upper limit of reproduced frequencies in the region of 7 - 8 kilohertz. Frequencies above this limit should be cut, as this is the "sand" area. It must be noted that in amplifiers and amps for classical (acoustic) guitars everything is exactly the opposite. Their frequency characteristics are very close to “musical” amplifiers. So we are talking only about amplifiers for electric guitars. For the same reason, “guitar” amplifiers are not suitable for listening to music.

In my mini-combo, I used an output transformer from an old tube TV. Such a transformer is quite suitable for a small guitar amplifier and fits well with the output tube, since the TV used exactly the same 6P14P tubes. The loudspeaker is connected to the secondary winding of the transformer through a regular telephone jack. This is a common solution in guitar amps. You can turn off the internal speaker and connect an external speaker to this jack. There is also a jack for connecting headphones. The headphones are turned on through a voltage divider across resistors R22 and R23. The divider is connected to the amplifier output automatically when the speaker plug is removed from the socket.

Schematic diagram of the power supply for a tube guitar amp

The weak point of my combo is the loudspeaker. Strictly speaking, the dynamic head used is not a “guitar” one; I didn’t have guitar loudspeakers at that time and I installed a Japanese 3 W speaker, torn out of some old Japanese radio. Although the speaker is not bad, it is not a “guitar” speaker, that is, it is quite broadband and reproduces frequencies that are not needed for the guitar signal, lying in the “sand” area. To some extent, this is compensated by the not very broadband output transformer and the presence of a tone control. But still, in acoustics for an electric guitar, it is better to use special “guitar” dynamic heads.

Switch Sw2 "Tone" turns on capacitor C14, which bypasses resistor R19 in the cathode circuit of the output lamina. At the same time, the sound becomes brighter and the output power of the amplifier increases slightly. Chain C11 R22 eliminates possible self-excitation of the amplifier.

The power supply unit of the combi is assembled on the basis of a unified Soviet transformer TAN16-220-50 (Anode-Nakalny Transformer). This transformer is very convenient for use in homemade lamp designs, as it has all the necessary voltages to power both the filament and anode circuits of lamps. however, you can use any transformer, for example from an old tube TV or a homemade one. The transformer must contain at least 2 secondary windings. Incandescent, for a voltage of 6.3 V (and a current sufficient to power the incandescent lamps) and a high-voltage winding with a voltage of 250 - 270 volts. In the case of the TAN16-220-50 transformer, I connected several of its secondary windings in series to obtain a voltage of about 210 volts. This transformer has 2 filament windings of 6.3 V. So I “bossed” and powered each lamp from its own winding. No one bothers you to connect the heaters of both lamps to one filament winding in parallel, if your transformer has only one such winding. The filament circuit of the first lamp includes a construction resistor R26 with a resistance of 470 Ohms. Its engine is connected to ground. When setting up the amplifier, turn the R26 slider, achieving a minimum of AC background in the speakers. the adjustment must be made with the R1 regulator set to the minimum volume position.

I used the winding of a 15-16 24 volt transformer to connect a power-on LED to it. Switch SW2 turns on or off the anode voltage. This is done in order to extend the life of the lamps. As is known, the service life of electronic tubes is reduced if the anode voltage is applied immediately at the moment the amplifier is turned on, while the filaments have not yet warmed up. Therefore, first we turn on the amplifier to the network, wait for the lamps to warm up (2-3 minutes) and then turn on the anode voltage with switch Sw2.

Mr. Shanti. June 2018

Chassis and mounting of a tube guitar amp amplifier. View from above

In the rating of guitar amplifiers, the tube amplifier deservedly takes first place. Decades of impeccable work and millions of positive reviews from musicians all over the world. What is the mystery of the popularity of a technology that was not even yesterday, but the day before yesterday? Let's find out together.

Lamp. This magic word is repeated like a mantra by all guitarists without exception. Even young, aspiring musicians know from the cradle that a tube guitar amplifier is the crowning achievement of the guitar amplifier industry. Professionals do not recognize anything other than the good old tube sound. A tube is what we strive for when learning the intricacies of playing the electric guitar, extracting the “wrong” and “fake” sound from our transistor amps. And while humanity is creating microcircuits, nanotechnology and learning to clone our own kind, we, in our quest to find perfect sound, we are going deeper and deeper into the past. By the very beginning of the twentieth century, because it was then that the lamp was invented.

So, we know that the tube amplifier is still the standard of true guitar sound to this day. But why? Are transistor, digital or hybrid amplifiers worse? Is it really true that after so many years the guitar industry has not been able to invent anything more modern, better quality and, finally, more progressive than a lamp?

Of course, she could, and invented it. But, let's take it in order.

The tube amplifier was invented in those distant times when the lamp (not to be confused with the ordinary incandescent lamp that we use for lighting) served as the main one for any electrical appliance. Then it was caused by simple necessity, since they still didn’t know how to do it any other way. Even then, such devices fully satisfied the tastes of guitarists. If you want clear sound, please. If you want overdrive, here's an excellent tube overdrive without any effects pedals. Of course, the lamp had its drawbacks. The obvious one is the difficulty of transportation. After all, a lamp is a rather fragile thing. In addition, tube amplifiers are quite bulky, and their cost is quite high. But the musicians turned a blind eye to all these little things. The main thing is that tube amplifiers provided excellent guitar sound.

Confused scientific and technical progress. First, transistor amplifiers were invented, and then digital ones. And, it seemed, everything was fine. An amplifier based on transistors turned out to be lighter, more compact, and more convenient to transport than a tube amplifier. And an amplifier based on a microcircuit (digital amplifier) ​​generally contains, in addition to the amplifier itself, dozens of guitar effects. What can we say about the price, such equipment has become available to almost everyone. It would seem that what else is needed. Buy, use and be happy, but that’s not the case.

A comparison of all types of amplifiers showed that the same lamp from the past managed to outperform all the new products released later. In all respects, the guitar sound amplified by a tube amplifier turned out to be much better than anything that transistors and microcircuits could produce. In fact, describing the sound of any amplifier is quite difficult. In fact, this is a very subjective assessment with which my readers may disagree. And, I must say, you will be absolutely right. Sound needs to be heard, not read about.

And today, almost all professional musicians prefer tube sound to all other types of amplification. This applies to both clean sound and overdrive. By the way, many musicians do not use guitar overdrive pedals at all, and get their j-j-j by simply overloading a tube amplifier. To please them, companies FENDER, MARSHALL and many others produce corresponding devices.

As you may have noticed, tube amplifiers are available both as a “head” and as a combo amplifier. However, there are also tube guitar preamps.

A preamp is needed to boost the guitar signal before it goes into the amplifier. It is connected to the circuit between the electric guitar and the amplifier. Moreover, various options for combining amplifying equipment are possible:

tube preamp + tube amplifier;

tube preamp + transistor amplifier;

transistor preamp + tube amplifier.

But in a combo amplifier, such a circuit is usually always used, and by plugging a guitar into the combo, we already get a chain: electric guitar-preamplifier-amplifier. Moreover, there are combo amplifiers in which the tube amplifier is only a preamplifier, and the amplifier is a transistor amplifier. Such combinations have an extremely positive effect on sound quality.

Yes, a tube amplifier is quite expensive. Yes, its heavy weight and the sensitivity of the lamps to shock make it inconvenient to transport. Yes, you can’t fully play with such an amplifier in your apartment, since you can only heat up the lamps and drive the speakers at high volume (no, I remembered, there are attenuators, read about them below). But even all these disadvantages are not able to reduce the popularity of the lamp.

It is clear that most often tube amplifiers are used at concert venues, in studios and at rehearsal facilities, that is, in those places where you won’t scare anyone with loud sound.

At home, if you really want to, you can play on a lamp using an attenuator.

This little box changes the resistance. By connecting it into the gap between the amplifier and the cabinet, on the one hand, you can warm up the tubes, and, on the other hand, prevent all the power of the amplifier from going to the speakers. But, in my opinion, all these are half measures.

Of course, I played with a tube, and transistors, and digitally. From what I feel I can only say that in digital amplifier no soul. Yes, the sound is not bad, and the effects are pleasing, and the compact size is very convenient, but no. The soul did not go to him and that’s all. The transistor amplifier, by the way, is the one I use at home now, I liked it better. Yes, it may sound a little dry and, perhaps, a bit rustic, but it’s just right for the home. Both in terms of volume control and in terms of unpretentiousness. The lamp is a completely different story. Perhaps I myself was subjected to a wave of general madness against the backdrop of the lamp, perhaps I simply could not accept that professionals could be wrong. But a tube amplifier is our everything. It's worth building your own house for this reason, so you can play without worrying about your neighbors at the volume you want, and enjoy this sound day and night.

The amplifier has all the attributes of its “big brothers” - prototypes. The presence of two controls (gain and volume) allows you to flexibly redistribute the gain of the circuit cascades to suit the desired sound. To expand functionality, the amplifier has two inputs different sensitivity, and changing the gain of the path allows you to get a sound from pure Clean to a powerful and dense Overdrive with Sustain. Equipping with an effects loop - Effects Loop - provides ample opportunities for experimenting with sound using external effects pedals or guitar processors. A two-band tone control provides deep adjustment frequency response amplifier Output switch for two nominal impedances (8 or 16 ohms) speaker system and a standby switch complete the look of the amplifier.

The amplifier was tested together with a Yamaha EG 112 electric guitar, with a set of S-S-H pickups, when working with guitar cabinets (loudspeakers) with dynamic heads measuring 6" (BCS 0608), 8" (Tesla), 10" (PSR1030), 12" (4A -32). For home use, it is better to use a speaker with a 6 or 8 inch driver, which does not create high sound pressure. In larger rooms, better results are achieved by using heads measuring 10 and even 12 inches.

In terms of nonlinear distortion, the parameters of this amplifier can be compared with the Fender Blues Junior amplifier (model 1995), which, with a power of 13 W at tone signal and a load of 8 ohms has a harmonic distortion coefficient of 5%, which is quite acceptable for guitar amplifiers.

Specifications

Input impedance (at connector X1), Mohm		1
Input resistance (at connector X2), kOhm		500
Input sensitivity
	Low, mV	22
	(in HG mode)	8,5
Input sensitivity
	High, mV	1,8
	(in HG mode)	0,8
	(with jumper S1)	0,8
	(with jumper S1+HG)	0,3
Load resistance, Ohm		8, 16
Output power, W, with harmonic coefficient no more than 5%		10...12
Integral noise level, dB		-68
Frequency range at level -3 dB, Hz		60...9000

Sensitivity values ​​for both inputs are indicated taking into account the combination of switching on jumper S1 and switch SA1 (HG mode), marked in parentheses.

Description of the circuit and features of the amplifier

Fundamental electrical diagram amplifier is shown in Fig. 1.

Fig.1. Guitar amplifier circuit diagram

The signal supplied to input X2 (High) is fed to the low-pass filter R1C3, which helps reduce HF noise and interference, and also prevents signals from broadcast stations from penetrating the input. The signal then goes to the pre-amplification stage. It is made on a low-noise nuvistor 6С51Н-В (VL1), installed on a separate printed circuit board. To reduce the cascade's own noise, the resistance of the grid leakage resistor is reduced to 510 kOhm and the anode supply voltage is reduced. The gain of the cascade is 10. When jumper S1 is installed, capacitor C5 is connected in parallel with resistor R4 and the gain increases to 30. To eliminate the microphone effect when using input X2, the amplifier should not be placed on speaker when operating at high power levels.

The Low input (connector X1) has lower sensitivity. The input signal is fed to the control grid of the 6N2P-EV triode (VL2.1) through the R6C6 circuit, which provides an increase in the frequency response of the amplifier in the range of 2...5 kHz. This creates a brighter sound for the instrument, known as Bright. The gain of the cascade is 50. To increase the stability of its operation, the anode load in the form of resistor R9 is shunted by capacitor 08, the capacitance of which also affects the frequency response of the amplifier.

The amplified signal from the anode load of the triode VL2.1 is fed through the isolation capacitor C9 to the gain regulator R12 - Gain. Capacitor C12, together with part of the resistor of the gain regulator, provides a rise in the frequency response in the region of 2...5 kHz, its effect stops in the upper position of the resistor slider. From the gain control the signal is supplied to the VL2.2 triode grid.

The VL2.2 triode cascade serves to amplify and compensate for signal attenuation in the tone block, and at high levels of amplified signals, to limit them. With a large gain of the previous stages and a high level of the input signal, the stage leaves the linear amplification mode - its overload and limitation of the amplified signals occur, which leads to the enrichment of the signal spectrum with harmonics and creates the characteristic buzzing sound of the Overdrive effect.

To increase the stability of the cascade at high frequencies, the anode load of the triode is shunted with a small capacitor, which also affects the frequency response of the amplifier in the high frequency region. The cascade gain is selected using switch SA1. When its contacts are open, the gain is 20, when closed - 48. To eliminate loud clicks during switching, resistor R15 is used, which ensures the flow of charging current to capacitor C13.

The signal from the anode load R17 through capacitor C17 is supplied to the tone control. The separation of the bass and treble control bands is in the region of 600...800 Hz. With the tone control knobs in the middle position, the block gain is approximately -22 dB. To limit the spectrum of amplified signals, a low-pass filter R29C21 is installed in the path; it determines the decrease in gain in the region of higher frequencies and filters out “non-musical” components of the spectrum. This has a beneficial effect on sound clarity when working with Overdrive. The high-impedance output of the tone block is connected to the input of the source follower on field effect transistor VT1, which eliminates the influence of the cascade on the operation of the tone block.

To expand functionality, the amplifier has a built-in “effects loop” - Effects Loop. The signal to external devices (effects pedals, guitar processor) is removed from resistor R13 of the source follower on transistor VT1 and through capacitor C16 goes to the level control R19 (X3 Send). To ensure the necessary load capacity of this output, the quiescent current of the transistor is set to 4 mA. The low output impedance of the cascade reduces the influence of the capacitance of the connecting cable and ensures normal operation with devices with an input impedance of at least 10 kOhm. Processed by external devices, the return signal is fed through the X4 Ret connector to the R26 level control. Input impedance at the Ret input is 50 kOhm, sufficient for connection external devices with increased output impedance. The presence of controls allows you to optimize the input and output levels of signals in the effects loop. If you exclude the elements of the effects loop, the resistance of resistor R30 must be increased to 1 MOhm, and the signal from the output of the low-pass filter R29C21 must be applied to the volume control resistor R30.

In the absence of external devices included in the effects loop, the signal from the output of the source follower through the volume control R30 (Master volume) is supplied to the input of the bass reflex stage, which generates paraphase excitation signals of the push-pull output stage. Various inclusions according to alternating current two phase inverter triodes causes a slight difference in the amplitude of the signals at the anode load resistors. Their alignment is achieved by selecting resistor R39. The gain factor of the bass reflex stage is 24.

The final stage (VL3, VL4) is made according to a push-pull circuit using beam tetrodes of 6F3P combined lamps, their triode parts are used in the bass-reflex stage. The final stage lamps operate with a fixed bias in AB1 mode, i.e. without grid currents. This bias makes it easy to optimize the operating mode to obtain maximum output power with higher efficiency while tolerating non-linear distortions.

Using the lamp quiescent current balance regulator (R40), it is possible to compensate for the spread in the modes of the lamps used to reduce nonlinear distortions and eliminate magnetization of the transformer magnetic circuit by the difference current of the lamps. Resistor R33 regulates the bias voltage, setting the required quiescent current of the lamps.

The quiescent current of the lamps (2x30 mA) is set by monitoring the voltage drop across the cathode resistors R47 and R48. Their resistance is 1 Ohm (deviation no more than ±1%). The voltage drop across these resistors, measured in millivolts, is numerically equal to the sum of the lamp's anode and screen grid currents, expressed in milliamps. The supply voltage for the anodes and screen grids of the final stage lamps is supplied through a damping resistor R53, which, together with capacitor C41, forms a filter that reduces the level of ripple in the supply voltage of the final and phase-inverted stages.

The power supply is built using a network transformer, which is relatively low voltage for such devices. The required anode supply voltage is generated by a rectifier with doubling the voltage on diodes VD4, VD5. To obtain a voltage of -47 V (for grid bias) and +49 V (for a stabilizer with an output voltage of +9 V), an alternating voltage from one section of the anode winding (-27 V) is used. During operation, the anode winding acquires a potential relative to the common wire of approximately +130 V, therefore, to “decouple” the rectifier bridge VD2, capacitors C32, C34 are introduced. In addition, this option of connecting diode bridges allows you to get almost double the rectified voltage. A similar role is played by oxide capacitors C31, C35 in a bias voltage rectifier with a diode bridge VD3. During installation, it is necessary to pay attention to the polarity of these oxide capacitors, since violation of this polarity will lead to their overheating and destruction.

The required current to power the lamp heaters is achieved by parallel connection of all filament windings of the transformer. The rectifier bridge VD6 with capacitor C42 provides power to the filament lamps VL1 and VL2 DC, which virtually eliminates the 100 Hz background.

To extend the service life of the lamps, the anode power should be turned on after warming up the cathodes of the lamps, and during breaks in the operation of the amplifier, it is advisable to turn off the anode power with switch SA4 (Stb).

The anode power to the phase inversion and preliminary stages is supplied through inductor L1, which, together with capacitor C26 and RC filters R5C1, R25C18, effectively suppresses supply voltage ripple.

Construction and details

The chassis is made of galvanized iron with a thickness of 0.6...0.8 mm. The advantage of this design is the availability of material and ease of manufacture at home. This chassis effectively shields the amplifier stages from magnetic and electric fields and has a pleasant appearance and is not subject to corrosion. A chassis blank with dimensions for the amplifier installation components is shown in Fig. 2. Dimensions (HxLxW) - 50x280x150 mm.

Fig.2. Tube Guitar Amplifier Chassis Drawing

After cutting the workpiece, even before bending, it is necessary to make all the holes for the installation elements. Then, at the bend points, on the inside of the chassis, using a cutter made from a hacksaw blade, using a metal ruler, make grooves with a depth of approximately 1/3...1/2 of the thickness of the metal, this will allow you to easily and evenly bend the chassis at the edge of the table. Solder the joints of the walls in the corners along the entire height. Additionally, brass posts with a diameter of 8...10 and a length of 6...10 mm with M3 threads are soldered into the corners of the chassis, this provides additional strength and rigidity of the entire structure. Subsequently, the bottom cover of the chassis is attached to these racks.

All printed circuit boards are made of foil fiberglass laminate with a thickness of 1.5 mm.

Drawing printed circuit board and the arrangement of elements on it preamp on the Nuvistor (VL1) are shown in Fig. 3 (rectangular holes for flat connector pins are formed by drilling with a drill collar). A drawing of the printed circuit board and the location of the elements of the bias voltage source and stabilized voltage +9 V are shown in Fig. 4. Similar drawings for the effects loop board are shown in Fig. 5, and for the output jack board for connecting acoustics and a protective resistor - in Fig. 6 (opening contacts are connected in parallel).

Fig.3. Preamplifier PCB Drawing

Fig.4. Bias Voltage Source PCB Drawing

Fig.5. Effects loop PCB drawing

Fig.6. Output Jack PCB Drawing

Decorative front and back panels made of aluminum 1.5 mm thick. Their dimensions are 280x60 mm.

The housings of oxide capacitors C18, C26, C39-C41, C43 are insulated with a heat-shrinkable tube. Capacitors C26, C41, C43 are fixed with tin plate clamps on aluminum plates 1.5 mm thick. The plates are mounted on tubular stands 10 mm high, with holes for transformer mounting screws.

Choke L1 is made from a TAG type subscriber loudspeaker transformer. Its new winding is wound with PEL-0.15 wire until the frame is filled. The cross-section of the magnetic circuit is 12.7x5.3 mm with a core height of 15 mm, although it is acceptable to use any other one with a large core volume. The plates are assembled side by side, without a non-magnetic gap; at low current values ​​this is acceptable. Inductance L1, measured without bias current, is 10 H, the active resistance of the winding is 145 Ohms.

Most of the amplifier parts are mounted using vertical mounting posts. To accommodate a number of elements that have terminals connected to a common wire, it turned out to be very convenient to use mounting strips 4...5 mm wide, made of foiled fiberglass laminate. The foil around the holes for the screws for fastening the strips has been removed. On the bar where the parts of the cascade with the VL2 lamp are mounted, pads are additionally cut into the foil for soldering parts connected by wires to other components; you can see it in the photo. The numbering of the lamp terminals indicated in the diagram is most convenient for installing the cascade. For power distribution of incandescent lamps VL1, VL2, a twisted pair of single-core wires with a diameter of 0.5...0.6 mm is made. The filament power supply for the final stage lamps is made with MGShV-0.35 twisted wires.

The pre-amplifier board output is connected to the VL2.1 triode stage using a shielded wire. The screen braid is soldered to the petals at both ends and connected to the chassis.

Capacitor C39 is installed on the chassis on insulating bushings. Its body is under voltage equal to half the anode voltage.

To prevent damage to the output transformer when the amplifier is turned on without a load, use a load resistor R54 with a power of 5 W (PEV or imported type SQP for 5-10 W) and a resistance of 20...30 Ohms. Filter resistor R53 (PEV 7.5 - PEV 10) is installed in the basement of the chassis. It also limits the charging current pulse of the capacitors when the anode voltage is turned on.

Fixed resistors of the effects loop boards and sources are +9 V and bias - MLT-0.25. The rest are MLT-0.5 or imported MF. It is acceptable to use some resistors and less power (see diagram). Variable resistors R12, R18. R28, R30 - SP-P or SP3-30, with an inverse logarithmic dependence of the change in resistance on the angle of rotation (group B). The use of group A resistors (with linear dependence) for regulators is undesirable; this will make it difficult to control gain and volume, especially at low levels, and will make the tone adjustment rough. The resistance of resistor R30 can be increased to 470 kOhm or more. The metal covers of variable resistors R12, R18, R28, R30 must be connected with a wire to the chassis. The housings R19, R26 of the effects loop board are also connected by a conductor (under the nut) to the common wire of the board. Trimmer resistor R40 - wire PP2-11, PP3-11 or PPB-1 B. Trimmer resistors R19, R26, R33 - SP4-1 with a power of 0.5 W. Resistor R53 - PEV with a power of 7.5 or 10 W.

Capacitors C26, C41, C43 are oxide K50-27. Capacitors C39, C40 - K50-12. Permanent capacitors in the anode and grid circuits of the cascades must have minimal leakage currents. You can use film or paper K73-17, K40U-9, BMT-2 and the like for a voltage of 400-630 V. Capacitors C32, C34 - K73-16V, possible replacement- K73-14. Capacitors in the tone block - K10-17.

Switch SA1 - toggle switch MT-1, switch SA3 - toggle switch MT-3. Switches SA2, SA4 are imported with a built-in indicator lamp (ballast resistors in the neon lamp circuit are not shown in the diagram). Connectors X1, X2, X5 - Jack 6.35 mm (ST-020) with two pairs of open contacts, connectors X3, X4 - with three pairs.

6N2P-EV lamps can be replaced by any of its modifications, and 6S51N-V lamps can be replaced with any Nuvistor triode (with some mode correction). When setting the anode currents of lamps of preliminary stages operating at low signal amplitudes, it is not advisable to increase the anode current above 1 mA; this will not improve their operation.

The network unified TPP252-127/220-50 is used as an output transformer; it is also possible to use an incandescent TN33-127/220-50. In this case, it is necessary to recalculate the transformation coefficient of the windings. The power supply uses a network anode-heat transformer TAN 1-220-50. The best replacement for it would be TAN 13-220-50 (without changing the switching circuit).

LITERATURE

1. Tsykina A.V. Electronic amplifiers. - M.: Radio and communication, 1982.

V. Ovsyannikov, Perm

Magazine "Radio" 2012, No. 2-3

Carrying things around sucks, and carrying heavy things around sucks twice as much. These statements are self-explanatory, but we guitarists must constantly accept them because our precious 4x12 amps and cabinets are often very large and heavy. And until we become rock stars with our team, we will have to carry these huge scum with our own hands. This is the heavy nature of guitarism. However, there is a way out of this heavy existentialism, and its name is miniature lamp heads.

It's time for little heads, my friends. Modern systems The sound reproduction and amplification are monstrously powerful and highly efficient, which means that no matter the size of the hall you're performing in or the size of your amplifier, even a small amp can rock an entire stadium. Stacks of big heads and cabinets are still pretty impressive and fun to play through, but none of that is necessary anymore. A small 15 or 20 watt amp and a small cabinet will do the job just fine at any gig under the sun.

With the growing popularity of such small devices, every company that produces amplifiers has a small, low- and medium-power tube head in their line. Without further ado, here are a few of our favorite miniature lamp beasts.

Tiny Terror is the prototype of the small tube head and it's still one of the best, so I'd be remiss if I didn't mention it. With the ability to switch from 15 to 7 watts of power, the Tiny Terror is the perfect size head for just about any gig, rehearsal or studio job it might find itself in. It can even power two 4x12 cabinets if you really need it. A pair of EL84s gives an amazing sonic range, both clean and distorted. Just one channel with three adjustments allows you to configure a warm wedge, meat crunch for classic rock, and there’s even enough gain for near-metal overdrive.

All in all, no matter how you look at it, the Tiny Terror is a great amp, and the sales level is proof of that. Not only did Terror do a great job for Orange, but this fiery little head revolutionized the entire industry. The Terror line has been expanded significantly since the release of Tiny Terror in 2006. A pair of high gain models for metalheads, the 30/15/7 watt Dual Terror, which has two switchable channels and more space in the sound, is especially good for those who like loud clear sound and pedals.

Night Train came along with the wave created by Orange Tiny Terror. And if at first glance everything seems similar in the British way: 15 and 7.5 Watts, two EL84 lamps, a practical and durable metal case. However, once you turn on, the differences become obvious. The Night Train has a rich, ringing, classic Vox ringing clean sound that is completely different from the guttural bark of the TT. And that defines its own place for this little Vox in the universe of tiny heads. Vox later updated the Night Train series with more more features and squeezing even more different sounds out of this compact form factor. Now there are two channels - British and Girth, which expands the palette from vintage Vox clean and drive to high-gain modern sound, and the Thick switch adds even more gain. Three-band EQ adds more granular sound shaping capabilities, while built-in reverb adds dimension to Night Train's sound palette.

German audio researchers at Hughes & Kettner have always specialized in a combination of musicality and innovation, and their Tubemeister 18 has definitely raised the bar for all small tube heads. Like many other similar amplifiers, the Tubemeister 18 contains a pair of EL84s, and as you can guess from the name, the head produces a maximum of 18 W of power. Perhaps this is where the similarities with products from other companies end. Unlike other EL84-based small amps, the Tubemeister 18 moves away from the midrange-heavy sound typical of these units and delivers a more modern, fuller spectrum, with an emphasis on clarity and elasticity on top of a vintage foundation. The amount of gain in its two channels is quite impressive, from scorching prickly clean to growling thrash and everything in between. The Tubemeister 18 also has two features that competitors do not have, for example, a built-in H&K Red Box DI output that allows you to record directly, and a Power Soak button that makes 18 W 5 W, and 5 W makes 1 W. power, the head produces a fat, rich sound, but at an acceptable power.

Many people know that Jet City is another Mike Soldano company founded with the mission of giving touring guitarists a pragmatic, ultra-reliable tube amplifier for affordable price. In many ways, the JCA20H is the embodiment of this philosophy. A pair of EL84s produce a real tube roar with balls. There is only one channel with gain control in the preamp, master volume, three-band EQ and Presence control, which uniquely regulates the flow of sound from your fingers to the amplifier. The Jet City JCA20H can deliver bright, sparkling cleans, soft but bouncy tube drive, and tight, fat crunch with equal ease. Turn on and rock out. What else is needed?

Quite often Laney is associated with their most famous endorser - Tommi Iommy from Black Sabbath. And the Ironheart IRT15H head is the true heir to this legacy of Destiny. While this 15-watt, dual-EL84 tube beast produces a wide range of great sounds, it's best suited for aggressive, high-gain destruction where other amps aren't quite as good. The Ironheart IRT15H simply has a huge amount of gain, so much so that many guitarists simply don’t need it. And his elastic low frequencies and ample sound shaping capabilities allow you to create frighteningly brutal metallic tones, even when operating in one-watt mode. This little Iron Heart can pack a punch at any volume level, making it perfect for trash monsters in the studio or on stage.