Tube guitar amplifier “MT Model 6 Amp”: 30W, CLEAN+LEAD, 6N2P, 6P3S

↑ Amplifier Features

The amplifier has two channels: CLEAN
for clean sound and
LEAD
for distorted sound.
Both channels have a separate three-band tone block - TREBLE / MIDDLE / BASS
, as well as several push-button switches, which make it possible to further change the frequency response.

The amplifier also has input/output ( SEND / RETURN

) to enable external effects. Channel switching can be done either with a push-button switch or with an external pedal.

↑ Guitar player diagram

The circuit is a compilation of various widely known amplifier circuits. It is given below.

The first stage is common to both channels. Then there is separation, the signal goes to the timbral block of the clean channel, and to the stages of the LEAD channel. The clean channel tone block has additional ROCK/JAZZ and DEEP switches, allowing you to further change the frequency response. The signal then goes to the second stage of the clean (CLEAN) channel. At its output there is an additional BRIGHT switch, which also allows you to change the frequency response in the high frequency region.

The cascades of the LEAD channel are made on the L2 lamp. At the input there is a WARM / FULL switch, which adds or removes lower frequencies, and at the output there is a CONTOUR switch, which also changes the frequency response of the channel.

The stage on lamp L3 is common to both channels. At its input there is a switch that switches the signal either from L1 (CLEAN) or from L2 (LEAD). At the output of this stage there is also a three-band tone block for the LEAD channel. For the CLEAN channel, the signal goes directly from the cathode L3 of the second triode.

The tone block of the LEAD channel has an additional SHIFT button, which changes its frequency response. The signal is then sent to the op-amp, which feeds the effects loop's SEND socket and a dual-pot MIX mixer. This potentiometer allows you to mix various proportions of the direct signal and the signal from the external effects unit coming from the RETURN jack.

After the general MASTER volume control, the signal goes to a standard bass reflex, assembled according to the “long tail” circuit, and then to the output tubes.

The output stage uses fixed bias valves. There is also a PRESENS regulator, often used in such cascades. Each channel has its own regulator, switching occurs using relay Rel3.

Since channel switching is carried out in several places, it is implemented on three 5-volt relays Rel1 - Rel3. The wiring diagram for these relays is shown in the lower left corner of the diagram.

Channel operation is indicated by two LEDs. The connector is used to connect an external pedal with a button.

Sergei Klimanski

For a long time I was unable to find an approach to the 6P3S lamp, but I have a supply of lamps, so I returned to this topic again. In addition, lately I have been less and less successful with amplifiers using triodes in the output stage - I have become an adherent of pentode sound. The internal resistance of the 6P3S in the pentode connection is 22 K, so the 3.5K output transformer I had in stock from James Adio should have been suitable even without OOS. In addition, it has an additional 16 Ohm winding for cathode OOS - and therefore the idea arose to make a circuit similar to the English Quad II https://drtube.com/audioamp.htm#Quad, only single-ended. In the preliminary amplification stage in the English device there is an EF86. A quick study of the data on the sound of this lamp led to the fact that it turns out that the 6Zh32P produced by Svetlana may sound no worse than its Western counterparts EF86. However, the high output impedance of the pentode was somewhat confusing, so the circuit provides for the installation of a 5687 matching lamp (you can install 6N30P or 6N6P) with the ability to turn it off with a toggle switch. The circuit also has a toggle switch for disabling the cathode OOS in the output stage.

Despite the presence of two pentodes, the sound of this amplifier turned out to be very good. With OOS, the sound is somewhat smoother, rounded (somewhat reminiscent of a triode), I liked the sound without OOS more. As for the cathode follower (CP), turning it off leads to a slight decrease in the level of the output signal and intelligibility in the middle and higher registers is somewhat lost, so I liked the sound of the version with the cathode follower more. What is good is that turning on the cathode follower does not lead to degradation of the scene and dynamics at all. An important conclusion is that the CP must have a direct connection at the input - an attempt to place a decoupling capacitor at the input of the CP and make a direct connection with the subsequent cascade leads to a simplification of the sound and a loss of its volume. The reason for this phenomenon may be that the input resistance of the CP is too high with the bias supplied from the cathode. An example of an unsuccessful design with CP is my project on the GM-70 (and I, in turn, tried to copy Ongaku

) - and I have already repeatedly been convinced of this in my earlier designs, for example, in the 6G7 - 6N8S - 6S33S circuit - there also, moving the separating capacitor from the output of the CP to its input with applying bias to the CP lamp (6N8S) from its cathode led to a very noticeable deterioration in sound - the stage becomes flat and the sound is inexpressive.

Operating modes of the 6Zh32P lamp – anode current 2.5 mA, voltage on the second grid – 160 volts. The filament is powered by alternating current, one of the terminals is grounded. The AC background is inaudible even at maximum volume. A pleasant surprise was that the lamp makes absolutely no noise or microphones, although there are a lot of bad reviews about the 6Zh32P on the Internet in this regard. My opinion is that the lamp is quite worthy of attention. As the only, very subtle drawback in the sound signature of this lamp, it is to a very small extent (in comparison with the best drivers on 12AX7 or 12AT7) the midrange is not expressive enough - this is more noticeable on plucked instruments - so classical music and jazz sometimes lack drive. Variety (rock, pop, etc.) go with a bang.

Network transformer – 100 W toroidal AS1T-320 from ANTEK https://www.antekinc.com/index.php.

Updated August 21, 2011. After running the amplifier for about 30 hours, I could no longer hear any difference in sound between the cathode follower version and the one without, so the 5687 tube was removed as an extra element in the final version.

Another important conclusion is that many Soviet tubes (including 6Zh32P and 6P3S) begin to sound more or less decent only after a good warm-up for quite a long time (at least 20-30 hours) - this is probably the reason for the poor ratings in the sound of these lamps by various authors (especially Western ones) - no one has the patience to wait that long. After all, Telefunken Philips and Valvo do not require such a long time to “build up” - they, as a rule, show what they are capable of after 1 - 2 hours. So you need to fry Soviet lamps, fry...... For the sake of interest, I compared the sound of the 6Zh32P with the Philips EF86 - (I ordered, but have not yet received other lamps) - in my opinion, the Philips sounds sharper (maybe microphoning?) and the bass is poorer - and I returned to 6Zh32P again.

Updated on August 23, 2011. Having made an adapter, I installed 1P33S instead of 6P3S. Yes, yes, here the difference is immediately audible even without warming up! - incomparably cleaner, more transparent sound with detailed elaboration of nuances throughout the entire frequency range - this is my dream - 1P33S is similar in signature to 2A3, but it is a pentode (more precisely, a beam tetrode)!!! The bass becomes clear, wide, rich, revealing many previously unheard nuances. True, there are also small disadvantages. It’s strange that in earlier projects with this light bulb I didn’t notice this - the 1P33S is highly microphonic, prone to self-excitation, and produces an alternating current background (I fed the filament with an alternating current) - probably, in a push-pull circuit these shortcomings are less noticeable. But you can fight all these disadvantages of 1P33S - it’s worth it, believe me. For comparison, I tried the famous EL34 Siemens, which on the market already cost 200 - 300 dollars per pair - but the 1P33S has noticeably better resolution in the lower register.

Added December 5, 2011. Now I am listening to this amplifier with a 5Ts4S kenotron, 6P6S at the output (without restructuring the output stage, but with cathode feedback) and EF806S Tesla (not JJ!!). What did these replacements give? 6P6S, other things being equal, compared to KT66 and 6P3S, has deep bass development, which is very beneficial for my Visaton V200 broadband speaker. And the Tesla light bulb has simply unsurpassed surround sound - none of the others I have tested gives such a deep stage (EF86 Mullard, EF86 Siemens, EF806S JJ, EF86/6267 EH, 6Zh32P have been tested).

↑ Amplifier chassis

Chassis drawing with inscriptions in Corel Draw, see Files

The amplifier is mounted on an iron chassis with a thickness of 1.2-1.5 mm and painted with acrylic paint in aerosol packaging. The inscriptions are applied using laser-iron technology and secured on top with transparent acrylic varnish.

General view of the amplifier from the side of the tubes and transformers.

General view of the chassis basement.

View of the main board, the CLEAN channel controller board and the SEND / RETURN board.

View of the filament rectifier board, ±15 V, LEAD channel controls and the main volume control board - MASTER.

Front view.

Back view.

The chassis turns out to be “upside down”

, because this is an amplifier for a amp and it must be attached to the top wall of the speaker. However, if I assemble it separately (with my head), the chassis will also be attached to the upper wall of the case. I haven’t decided yet whether to make a combo or a head, but almost all companies do just that, upside down!

Tube guitar amplifier (distortion and clean)

For some time, having given way first to transistors, and then to microcircuits, radio tubes again returned to the closets of radio amateurs. Currently, these electric vacuum devices have gained great popularity among lovers of good sound. This applies to both musicians and those who listen to their recordings. Numerous companies have responded to the demand and in stores you can now buy a decent amplifier without much hassle, but their cost in some cases is simply astronomical. As a result, many radio amateurs master the basics of building equipment using radio tubes, constructing various amplifiers for their headphones, powerful audio systems and musical instruments. And I didn’t “pass” by when I decided to work on an amplifier for my guitar.

As the basis for the future design, I took the well-proven Slo Recto Twin designed by Gishyan *AZG* Aznaur, well-known among tube music enthusiasts. To the “pre” I added a push-pull power amplifier based on 6P3S beam tetrodes, a delay circuit for the supply of anode voltage and switching with a footswitch.

Schematic diagram

Structurally, the amplifier consists of a pre-amplifier using VL1-VL3 tubes, a push-pull power amplifier (VL4-VL6 tubes) and a common power supply.

The preamplifier, in turn, consists of two channels - clean and overdrive ( distortion ) with separate tone and volume controls.

The signal from the guitar pickups is fed to the grid of one of the two triodes of the VL1.1 lamp, which is a common amplifier for both channels. In the cathode bias circuit of the triode, using one of the groups of relay contacts, the electrolytic non-polar capacitor C1 is switched, which is included in the circuit in pure sound mode and expands the band of amplified frequencies in the low-frequency region. In overload mode (the relay is activated), it is isolated by the high resistance of resistor R3, so only capacitor C2 remains, which has a relatively small capacity. At the same time, the gain of the cascade is noticeably reduced at low frequencies, which prevents the “booming” of the sound. From the anode of the triode, the signal is divided into two channels. The top one operates in the mode of amplifying pure sound, the bottom one is in overdrive. clean channel is represented by a three-band ( treble - high, bass - low, middle - middle frequencies) tone control, assembled according to the fender circuit, and an amplification stage on the VL1.2 triode.

Overload ( distortion ) has already been implemented by a much larger number of lamps and passive elements. Three stages based on triodes VL2.1, VL2.2 and VL3.1 have a large total gain, due to which the sound is greatly distorted. This creates an effect with a characteristic heavy and powerful sound. To coordinate these stages with the tone control, as well as to prevent mutual influence, a cathode follower on the VL3.2 triode is included in the circuit. In pure sound mode, the overdrive channel is blocked by shorting the VL2.2 triode grid.

To separately regulate the signal level of the cascades, each of them is equipped with variable volume resistors R11 and R38. In addition, there is a general volume control R40 master volume. The engines of all volume controls are shunted with fixed resistors with a resistance of 2.2 megaohms. They are necessary to eliminate possible rustling noises caused by wear of the conductive layer. In themselves, they are not terrible, but in this case the mesh is separated from the common wire, as a result of which the volume of the rustling becomes very loud.

The amplified and processed signal from one of the channels is fed to the input of a differential phase inverter assembled on a VL4 lamp. Its task is to additionally amplify and create two identical signals at the output with a phase shift of 180 ° relative to each other to operate a push-pull power amplifier using 6P3S tubes.

Switching of the pre-amplifier channels is carried out using two relays, which, in turn, are switched using a footswitch (you can select the desired channel by pressing the foot of a button, like in a lotion) or a switch on the front panel. There are also bright (S1) and treble shift (S2) mode switches to change the sound color of each channel. The indicator LED VD13 in the footswitch is included in the circuit of switching relays and lights up when the S6 button is pressed to turn on the distortion . Capacitor C57 with a relatively large charging current at the moment the button is pressed ensures reliable operation of the relay, since the current flowing through the LED may not be enough for this.

The amplifier is powered by a transformer power supply with passive anode voltage filtering with a delay circuit, and with a 12AX7 lamp filament voltage stabilizer. The anode voltage rectifier uses ultra-fast UF4007 diodes, thanks to which it is possible to almost completely eliminate the switching noise of diode switching. To ensure that power is supplied to the lamps only after their cathodes have warmed up, the amplifier uses a delay circuit assembled on transistors VT3 and VT4. Relay K3 is activated approximately 10-15 seconds after the amplifier is turned on (selected with capacitance C55) and closes contacts K3.1. The filaments of the pre-amplifier lamps are powered by a stabilized voltage of 12.6 volts to reduce background and noise, as well as to increase the service life of these vacuum devices. The voltage at the cathode of the VL3.2 repeater is quite high due to the high resistance of resistor R33, because of this a significant potential difference is created between the cathode and its filament, which greatly reduces the operating time of the lamp. To neutralize this effect, the filament potential “rises” relative to the common wire by approximately 75 volts. The corresponding voltage is supplied from the divider R67 and R68 to the symmetrical filament divider R65 and R66. The same divider is installed in the filament circuit of the output lamps (6.3 volts), but its middle point is connected to the common wire.

The ground decoupling is made according to the “star” scheme, when the wires from the common wire circuits of different stages are connected at one point and have reliable contact with the amplifier body.

Details

All amplifier fixed resistors must be metal film (MF) or metal oxide (MO). They have less noise, unlike carbon CF resistors. Domestic MLT resistors are also suitable.

Film capacitors must be of the MKP series from Wima or Epcos for a voltage of at least 400 volts. These “musical” capacitors are quite common. You can also use good domestic K71 series. Consumer-grade K73 produces slightly worse results. You should beware of old metal paper capacitors such as MB or MBM. As a rule, even the “newest” copies are more than 30 years old and almost all of them have significant leakage currents. Electrolytic capacitors are best used with a maximum operating temperature of 105 degrees due to their proximity to hot lamps. For capacitors in anode circuits, the voltage must be at least 400 volts. The 0.022 μF capacitors shunting them must be of type X2, designed to operate in an alternating voltage circuit of at least 275 volts. Their operating DC voltage is 600-1000 volts, and their low internal resistance to pulse current contributes to good filtering of noise and ripple. Instead of non-polar electrolytes C1 and C10, conventional polar ones can be used. For small-capacity capacitors in tone blocks and in the bass reflex, it is better to take film, mica from the KSO and SGB series or imported high-voltage blue ceramic capacitors.

The preamplifier uses Russian-made 12AX7 tubes from Tung Sol. Instead, you can use ECC83 or domestic 6N2P-EV. In this case, the filament voltage should be reduced to 6.3 volts. To do this, you need to replace the VD9 zener diode with another one - with an operating voltage of 3.3 volts. With some deterioration in sound quality, you can use 6N2P, 6N23P and even 6N9S, as well as other double triodes. Common domestic 6P3S tetrodes are used as output lamps.

Transistors in the delay circuit, as well as VT2 in the filament stabilizer of the preliminary lamps, can be any silicon low-power npn structures and with a minimum emitter current transfer coefficient of 100. For example, KT315, KT3102, SS9014, and so on. Powerful transistor VT1 must have a maximum collector current of at least 4 amperes and a maximum voltage of at least 100 volts. If its body is not insulated (TO-220FP), then it should be attached to the radiator through an insulating heat-conducting gasket “Nomakon”, and the tightening screw should be equipped with a plastic washer.

It is advisable to use ultra-fast diodes in the anode rectifier VD1-VD4, such as UF4007, but you can also install regular rectifiers with a maximum reverse voltage of at least 600 volts and a forward current of 1 ampere. In this case, each of them is shunted with a film or ceramic capacitor with a capacity of 0.01 μF to a voltage of at least 630 volts. Diodes VD5-VD8 with a Schottky barrier, they can be replaced with any with a maximum forward current of at least 3 amperes.

I used specialized relays for switching audio signals - 46ND012-P from FUJITSU. But you can use any with an operating voltage of 12 volts, with two switching groups and a minimum operating current.

Transformers and chokes are homemade. The first ones are wound on frames and cores from the Russian Corvette computer manufactured in the mid-90s. Their U-shaped tape magnetic cores have a small dispersion field and can be installed without magnetic shields. Any transformer iron with a cross-section of 6 cm2 is also suitable. Data on windings and voltages are given in the table in the diagram. Between the layers, one layer of varnished cloth or thin capacitor paper should be laid, and between the windings the number of layers should be at least three. Between the halves of the magnetic cores there are insulating pads made of varnished cloth, 0.3 mm thick. The chokes are wound with 0.25mm wire until the frames are filled. Their cores must have a cross-section of at least 2 cm2 with a dielectric insulator between their halves.

Design

Attention! This amplifier, like most other tube devices, contains high voltage that is dangerous to life and health, so all installation work and adjustments should be carried out in compliance with safety precautions!

Structurally, the amplifier is made on an open duralumin chassis, repeating the design approach to the design of tube audio amplifiers. Variable resistors, almost all connectors and switches are mounted on the front panel, which has an easy-to-use bend at an angle of 45 degrees. The sockets for fuse FA1 and the output of the audio transformer, as well as the power connector, are located on the rear wall.

The footswitch is assembled in a separate durable case, connected to the amplifier by a long cable.

The printed circuit board is quite long, so the thickness of the foil fiberglass laminate must be at least 3 mm to prevent unnecessary deformation. If you cannot find such material, then you can use the common one with a thickness of 1.5 mm, but you must provide holes for attaching the stands in the middle of the board.

Setup

Despite the rather large complexity of the circuit, the amplifier begins to work immediately after switching on, if, of course, all the parts used in it are in working order. However, the operation of the device should be checked step by step. First, the amplifier is turned on without tubes and the operation of the delay circuit is checked. Next, by adjusting the tuning resistor R63, the filament voltage of the pre-amplifier lamps is set to 12.6 volts. Next, already with the lamps, you must again adjust this voltage, which will “fall” under load. After this, the voltage on the anode supply capacitors is measured. It should be 330-360 volts. It should be noted that for a working amplifier these figures will be lower.

Next we insert the power amplifier lamps VL4-VL6 into the corresponding sockets. A shielded wire is temporarily soldered to the upper terminal of the variable resistor R40 in the diagram, the second end of which can be connected to any audio source - a player or mobile phone. At the same time, clear, undistorted music should be heard in the speakers. Next, insert the VL1 lamp into the sockets and connect the guitar to the input of the amplifier, which is switched to the “clean” channel. Make sure it works well. Then they insert the remaining lamps and check the distortion channel.

The lamp modes are selected optimal, and they remain so when using resistors with a standard tolerance of ±5%, so no selection of elements is necessary.

Together with this amplifier, I use a cabinet (“speaker” for guitar amplifiers) with a Vintage 30 speaker from Celestion installed in it. It is not recommended to install conventional speakers used in car and household speaker systems, since it is the guitar speaker with its special frequency response shape (mid-frequency rolloff) that creates the special sound of an electric guitar.

List of radioelements

Attached files:

• Payment.lay (116 KB)
• overload.rar (2283 KB)
• clean.rar (1463 KB)

Tags:

• ULF
• Sprint-Layout

↑ Power transformer

OSM-0.16 with a network winding of 220 Volts is used as a power transformer.
The power transformer has five secondary windings. They serve to obtain anode voltage, filament voltage 1 and filament 2, bias voltage winding and winding to obtain ±15V. The first, after the network winding, is the anode winding. It contains 60+680+680+60 turns of wire with a diameter of 0.33mm. An additional 60 turns are made to increase the anode voltage and increase power when using 6P3S-E output tubes instead of 6P3S. Then the bias winding and the ±15 Volt winding are wound. To obtain the bias voltage, a winding of 140 turns is used, and a winding of 70 turns is tapped from the midpoint to obtain voltage. The wire for these windings is 0.17mm in diameter.

The last to be wound are the filament windings. Winding 15 turns with 1.4mm wire. used to power the filament of output lamps, and 16 turns of 0.95 mm wire to power the filament rectifier for 6N2P lamps.

The interlayer insulation is tracing paper; between the windings I used packaging, so-called kraft paper, but you can also use varnished cloth.

Smoothing throttle

made on iron Ш16х20 and wound with 0.25 wire until the frame is filled.

6p3s - tube amplifier, single and dual push-pull stage

The article planned here is devoted to a review of simple tube sound amplification circuits built using traditional single transformers with a midpoint. The tube circuit is definitely push-pull. Those who like single-ended amplifiers can cut off the excess in the circuits and get themselves a stub that is about half cheaper in terms of components. At the same time, they can go to the clinic and have themselves circumcised, or better yet, completely castrated. For a normal push-pull amplifier on 6P3S, it is desirable to have matching transformers with a reduced resistance of 5-6 kOhm, but you can also adapt standard rod transformers designed for higher voltages (127V + 127V) and having several additional windings. An important condition for using the right transformers is their timely diagnosis for the minimum possible no-load current. Based on the no-load current, the lower limit of the amplifier bandwidth is initially approximately estimated. The calculation of the self-inductance of the matching transformer is performed extremely simply - according to the first gaamonics. The mains voltage is divided by the measured current and then by the angular frequency, neglecting the resistive resistance of the windings. The resulting inductance value in Henry should be at least 20, and preferably 40-50. As soon as it is possible to select a pair of identical transformers, the task of creating an amplifier can be considered practically solved. For those who are tight, I repeat, you can’t just take two arbitrary TC transformers off the shelf and build a tube amplifier on them; first you will have to measure the XX current with an electromagnetic milliammeter. If you don’t like the use of standard transformers, then calculate and wind your outputs for a given load resistance. This is a longer trajectory. To guarantee the quality of the amplifier, you need to know how to design matching transformers.

After you manage to touch the output transformers with your hands, you can bother looking for lamps. Many Soviet lamps are suitable for 5-6 kOhm. If the transformer is not very powerful (up to 100W), then you can limit yourself to one pair of output lamps. If the transformer turns out to be more powerful, then you can hook two pairs into one channel. But you will have to select the lamps. In addition to being certain about the output transformer and light bulbs, you should understand what kind of power supply is needed. The simplest option would be to use power anode transformers at a frequency of 50 Hz. You will need a fair amount of power for 6P3S lamps. In each channel, the anodes will accept 20+20 watts. The same amount can be allocated to the load. In total, 2 channels will require at least 120 watts. Smaller llamas also have consumption, and will also require power in the incandescent circuits.

The appearance and connection diagram of the 6P3S output beam tetrode are shown in the figure. In my deepest conviction, it is the 6P3S lamp that should be considered the most successful among the lamps made by Sovdepov. The 6P3S lamp is distinguished by good electrical parameters, high permissible anode voltage, high power and excellent stability. And these lamps glow very beautifully. You need to load the lamps to capacity, and also apply 400 volts to the anodes. Then a bright crimson glow and deep blue glare will appear throughout all glass containers. Well, a lot of heat will be a by-product.

In my opinion, the 6P3S lamp is a universal motor for numerous lamp designs. It has very good characteristics and hefty power dissipated by the anode. This distinguishes the 6P3S lamp from its numerous flimsy analogues. In my opinion, this Soviet sample is in no way inferior to foreign “cool” lamps, especially taking into account the price difference. And the price can differ favorably by 100 times or more, although the vacuum in the lamp is the same. Below is an example of a curious 6P3 lamp, which became the starting point for the creation of the modern 6P3S lamp. The year of manufacture of this lamp is 1951, there are samples that are even older, but in excellent working condition, quite suitable for building a tube amplifier.

Lamps of type 6P3S-E are other lamps that differ in design from 6P3S. In terms of operating parameters, 6P3S-E is also somewhat different from 6P3S and should not be placed in the same team. Most of the 6P3S-E lamps I have measured are characterized by a significantly higher slope of the characteristic. An increase over 6P3S was registered up to 50%. But the excess in the anode current is quite insignificant. A common feature of lamps with the indicated name is the considerable power of the anode. When tested on an L1-3 lamp at an anode voltage of 300 volts, the lamps withstood an anode current of 130 mA for a long time, literally for hours. And this means a huge limit of stability, because there were always 39 watts in the anode! Of course, such modes should not be included in the designed structures. But understand that dynamically such powers are quite achievable for lamps of the 6P3S family. Lamp structures need to be configured according to the datasheet parameters. The stability of the thermal regime and the response to control input for all working lamps of this name are simply excellent.

The continued functionality of electronic tubes is entirely determined by storage conditions. Considering that some lamp samples are 70 years old or more, their objective cost today is quite high. According to reviews from DIYers, the characteristics of this lamp are quite smooth and provide a very soft, comfortable sound. In practice, this will have to be tested in the near future when creating the next tube amplifier design. By the way, I can say that on the Internet I could not find the characteristics of this lamp, as well as examples of descriptions of structures obtained with its use.

A smaller version of the 6P3S beam tetrode with similar characteristics is shown below. This is a 6P6S tetrode with an octal base, a very decent light bulb. Simply replacing a 6P6S with a 6P3S lamp in a standard octal socket will not in any way affect the operation of most devices. Most likely, even audiophiles will not notice the substitution. And if you adjust the instrument mode to minimize distortion, then there will be no difference at all. Replacement is not advisable, since the 6P6S lamp may not be able to carry the power load allowed for the 6P3S.

Once again I must say that the traditional, ingrained in people’s minds, approach to presenting an article from the name and choice of lamps is not reasonable and incorrect. It is obvious to everyone that it is unwise to start choosing a car with the engine and wheels, since first they evaluate the purpose, cost, aesthetics, functionality and other characteristics. Common sense suggests that the most important component of a tube amplifier is the output transformer. The quality of the entire amplifier depends on its quality. The cost of the output transformer can be 80% or more of the cost of the entire project. Everything depends on the choice of transformer, its manufacture or purchase, including the choice of the appropriate type of lamps. If my presentation of the material follows the traditional order, then most often it has a different purpose. I don’t want to show convenient and common transformers. They are quite easy to calculate yourself using raster images on the website. At the beginning of the article, we should show several simple push-pull circuits with single lamps. For such circuits, relatively weak output transformers are suitable, for example in the TS-40 size. I have said it many times and will repeat it again, a banal truth. For a push-pull amplifier of the simplest level, you can use almost any domestic rod transformers with the correct wiring of the windings. Feel free to send three letter letters to advisers who insistently recommend winding transformers yourself. Most likely, these people are captive of dogma, or they are cunning people who want to complicate your path to the desired result, or they are narrow-minded. Another option is possible: These advisors want to make some money from your interest in lamp technology. Well, they have the right. Confidently step forward without looking back at your advisors. Find your way. And remember, the shortest trajectory is shown here.

When building a tube amplifier, most people do not need to manipulate the winding units. Usually, the clever words of the authors about hand-to-hand winding of the output transformer cause a stupor and ruin the not yet matured project in the bud. An ordinary amateur TV viewer may need detailed labor costs relatively later, when there is a conscious interest and understanding of the necessary changes. Or they may not be needed at all, which is typical for 90% of beginning lamp makers. Good results of the first level are obtained by using ordinary armored transformers with separate primary windings of 127 volts as output transformers. However, the use of rod transformers is an order of magnitude more profitable, since there are compact and convenient serial transformers. Their use immediately gives results that are economical in time and resources, and equally high-quality results in sound.

In any application of trances, it is preferable to have two windings designed for 127 volts. And if there are more symmetrical windings, then this is even better. For example, in comparison with a 127V armored transformer, its complete analogue, but designed for a voltage of 220 volts, is simply unsuitable for a push-pull amplifier, since it has a single winding. In addition, as a rule, a typical 220-volt industrial transformer has a huge no-load current and a large stray field. This precludes its use in a lamp design, even as a power source, since it provides an invincible background of alternating current. Transformers with 220-volt windings are headed for the trash heap, since they sometimes ring even at idle.

Rod transformers with 127 volt windings are more profitable to use than similar ones, but with 110 volt windings. This is obvious, since each such winding has 15% more turns. Consequently, the inductance is greater and therefore the left limit of the frequency response will be lower, and the low-frequency range will be expanded. Output transformers for ultra-linear switching 6P3S must have taps symmetrical relative to the center with a number of turns of about 43% of the number of turns of each arm. The same rule should be observed when constructing a differential connection circuit for a pair of transformers. As you know, the pinout of the 6P3S lamp is similar to the 6P6S lamp. In most cases, this allows you to use 6P3S instead of 6P6S, and a significant part of TV viewers, especially fans of amplifiers with a triode-pentode switch, will not even notice such a replacement. The usual replacement of these lamps in low-power circuits is painless. Of all listeners, no more than 0.1% will understand that the sound is slightly different. When changing and adjusting the mode, you need to remember the difference in characteristics. It is advisable to have ultralinear transformer taps, for example for 6P6S, with a number of turns of about 23% of each arm. And since the power of the anodes of these lamps is different, replacing 6P3S with 6P6S is completely unacceptable.

Attention! All transformers for lamp designs should first be tested for no-load current. Only transformers with small no-load current should be used in hand-to-hand developments. All other transformers should be sold or scrapped. At the second stage of choosing transformers, you should carefully consider the issue of balancing transformers, both in terms of inductance and EMF value (magnetization characteristic). Only after careful selection should you tell your loved one that high-quality output transformers suitable for construction have been identified. Collective farmers will think such efforts are unnecessary, since they are sure that standard transformers do not sound at all. That is why such dancers disparagingly call standard transformers “green stuff.” If the qualifications of such specialists were higher, and their self-confidence was weaker, then the phrase “collective farmer dancer” would remain unused.

It is better to perform both calculation and tuning of a tube push-pull amplifier from the output. Before setting up, the first lamps can be completely removed from the panels. First, for the output stage, the bias regulator sets the quiescent current within reasonable limits and thoroughly warms up the anodes of the lamps. After warming up, the quiescent current is clarified. General feedback is turned off at the beginning of mode regulation. After setting up the output stage, you can remove the output tubes and insert the input ones. The DC mode is controlled by a resistor in the cathode of the first half of the input lamp. Then the AC mode is adjusted using a resistor in the cathode of the second half. The symmetry of half-waves, the presence of any debris and excitation are monitored using an oscilloscope. Manipulations with the removal of lamps allow you to accurately control the moments when jambs occur and immediately determine their causes. I do not recommend immediately connecting speakers to the output of the transformer. Instead, you must include a load resistor. This will relieve noise and stress from sudden excitement. At the final stage, all lamps are inserted into the sockets and the end-to-end signal path is checked. You need to understand that modes under filament load can drop by 10% or even more. And if you apply a sine wave to the input, then the drawdown along the anodes will be quite hefty. Therefore, final manipulations should be carried out to configure the amplifier modes under load. Then they return (or do not return) feedback in the correct phasing and evaluate the frequency response.

The voltage of +400-450 volts for 6P3S screen grids is, to put it mildly, too much, so it is better to transfer their power to the preliminary stage, through additional AC OOS windings. It is possible to build a parametric stabilizer with powerful stadditrons, approximately 250 volts from the anode voltage of 450 volts. But if you need more power, you can turn it on directly, but through damping resistors, and there is no other cheap way to achieve the goal. 6P3S lamps can withstand such abuse. The current limiting resistors will have to be significantly increased in value. But this will have virtually no effect on the quality, which in a circuit with a large excess voltage across the grids will be mediocre. Schemes with differential connection of output transformers seem to me much more relevant and interesting.

The following are circuits with only dual lamps in each arm of the output stage. Due to the size of the 0.16 kVA output transformers, no one would mind paralleling 3-4 lamps in each arm. In this case, it will only be necessary to more thoroughly select them according to the value of the anode current. A selection accuracy of 10% is quite sufficient. Do not believe the impudent people who easily add the power of ULF channels into one equivalent value to obtain impressive figures. This is a lie. The equivalent output power value in practice will be significantly less. Below are diagrams with additional drivers before output. Practice has shown that it is better not to use a driver for 6P3S. There is enough sensitivity and gain in the circuit even without a driver. And the presence of additional lamps and installation flaws often lead to self-excitation.

In a balanced bass reflex circuit, the halves of the triodes should be carefully selected. In the load-sharing circuit shown in the picture, selection is not necessary. Actually, that’s why in the first stages of lamp construction it is better to master the experience of Williamson’s grandfather. The use of trimmers in the triode cathodes will allow you to slightly tailor the curvature of the lamp halves, if there are flaws in the selection according to the symmetry condition. You will notice that in many circuits it is easier to install a trimmer than to look for exact values, much less select resistors in fractions of a percent. I do not recommend installing trimmers in anodes. As a recommendation for improving sound quality in a load-sharing circuit, we can recommend selecting a double triode according to a different rule. The first triode in the circuit can be relatively low-current, but with a high transconductance. And the current of the second triode can be up to one and a half times greater. It is precisely these double triodes that are best used for the Williamson circuit, since the current in the phase inverter, as a rule, is much larger.

In some nodes, the use of trimmers is mandatory, but in others it is a whim. At the prototyping stage, the trimmers can be adjusted. This is convenient when a printed circuit board made of foil PCB is used as the supporting base of the amplifier. Then the trimmers are soldered directly onto the board tracks, installed vertically. If the amplifier case is turned over on the mounting table, the entire basement space is open to access. The control possibilities are large; it is convenient to configure each unit, controlling the modes using the devices. Output transformers can be very useful. Human imagination is not limited. Their equivalent power should be four times the required output power. Usually they focus on the power dissipation of a pair of anodes of the output stage lamps.

Below is shown the use of a mounting table for building a tube amplifier, when installing parts into a finished housing. When designing amplifiers, it is better to reach in advance the overall increased dimensions of the housing, suitable for both powerful products and for an ordinary push-pull 6P14P. Usually the costs for the housing are quite significant, so it is advisable to unify the housings in advance. The mounting table is just a convenient device that allows you to protect the case from numerous damages. An assembly table is simply a frame made of wooden blocks, similar to a stool without a saddle, but a very convenient contraption. You can equip the mounting stand with additional removable rails, then a smaller enclosure can be serviced with the same device.

Citizens, remember, there are almost always errors in circuits, but correcting them is not difficult; you need to be more careful both when constructing the circuit and during installation. Tube circuitry is very tolerant of errors. In most cases, it is extremely difficult to damage transformers or lamps. Anode DC voltage sources are quite dangerous. Therefore, caution should be exercised.

To save time, we can advise you to immediately arrange your needlework in a decent form. The fact is that a pile of junk with tangled wires on the table is not only unsightly, but also hazardous to health. Besides, it's double work. It is better to first spend a little time and invent a mechanical structure of a cultural appearance, inside of which your ugly but beloved creation will later be hidden. And it’s even better to immediately make a beautiful design.

Bulbs 6P3S and 6P3S-E are quite nice in appearance. There is a supply. That's why they are sold here, but only in matched pairs. You can also buy a 6P3S tube amplifier here at a price of 50K and above. To do this, just contact me by mail, discuss the price of the product and delivery conditions, pickup is possible. After this, the person interested should call the phone number indicated on the website to discuss the details, and only then make an advance payment of 20% of the agreed amount to my Sberbank account. Having received the transfer, I send a notification and within two weeks I will call you back with confirmation of proper packaging of the product and readiness for shipment, and I will send photographs of this particular unit, opened and packaged, by email. For shipment, the buyer is required to transfer the remaining amount, after receiving which I carry out the shipment and email a copy of the receipt. If the buyer's circumstances have changed within the specified period of time, then the purchase can be refused. The listed deposit is not refundable. The amplifier has a 12 month warranty from the date of delivery. The warranty does not apply to glass sent by post or transported by a transport company. Sincere wishes to everyone for good health and success.

Evgeniy Bortnik, August 2015, Russia, Krasnoyarsk

↑ Output transformer

The output transformer is wound on iron from OSM-0.1 and is designed to connect loads of 8 and 16 Ohms.

Winding layout and switching diagram

The primary winding is made of wire dia. insulation 0.27. and the secondary windings are made of wire dia. insulation 0.68 for sections of 8 ohms and dia. insulation 0.8 for an additional section of 16 Ohms.

Tracing paper was also used as interlayer insulation, and kraft paper or varnished cloth was used as interlayer insulation. I didn’t use any paraffin treatments; I used to wrap it like this before, and it was fine! The main thing is to ensure sufficient winding density, which, unfortunately, comes with experience. But you can boil it if you want.

↑ Checking the phasing of the sections of the primary winding of the output transformer

We connect the generator to the terminals of the secondary winding GRND - 8Ohm and apply a voltage of 1 Volt, 1000 Hz from it.
We connect the oscilloscope ground to point A+ and measure the voltage at points A1 and A2. They should be equal and out of phase and with an amplitude of ~ 15 Volts. If it is less and/or not the same, then it is necessary to change the beginnings and ends of the sections of the primary winding. I would like to draw your attention to two options for the location of the output transformer. Closer to the output tubes or closer to the input tubes. Based on the results of background measurements, it seemed to me that the best option was to locate the output transformer more remotely from the output lamps and the power transformer.

↑ Assembly and parts of the amplifier

To switch channels, three relays designed for 5-6 Volts are used.
The negative of the 6.3V filament source is connected to a common ground. The connection of the ground wire to the amplifier body is made on the main printed circuit board in the area of ​​the input contacts. Signal inter-board wires are shielded. Moreover, the screen is connected to the ground only at one end. The connections between the main board and the lamp sockets are made with single-core wires of minimal length.

Only fastenings to the chassis of control components and connectors are used to secure the regulator boards and input/output connectors.

Voltages of ±15 V are obtained using three-terminal regulators 7815 and 7915.

The amplifiers use MLT type resistors. All resistors, except those indicated separately, have a power of 0.25 W. Where high-power resistors are required, they are indicated separately in the diagram.

The amplifiers use Soviet K73-17 capacitors, designed for a voltage of 400V, as isolation capacitors. C17 is also like K73-17, but at 63V. C4 and C12, located in the cathodes of pre-amplifier lamps, recommend using tantalum or oxide semiconductor. I have the K53-19 type, but you can try others.

Capacitors C19 and C34 are high-voltage ceramics for a voltage of 1000 V, which I took from computer power supplies. The remaining electrolytic capacitors are ordinary aluminum ones.

The choice of the type of capacitors located in the signal circuits and forming the amplitude-frequency response of the amplifier depends on the thickness of the wallet and the capabilities of the replica design.

The amplifiers use push-button switches of the PKN-61 type. I would also like to draw your attention to two 10 Ohm resistors located in the ground bus on the main board of the amplifier and dividing it, as it were, into three parts. They are not shown on the circuit diagram, but are on the printed circuit board. They are installed to decouple the ground of the output and preliminary stages and serve to reduce the background.

SINGLE CYCLE TUBE AMPLIFIER – DESIGN

During my amateur radio career, I have assembled and tested more than a dozen different tube amplifiers - both push-pull and single-cycle, including those with parallel connection of several output tubes. Most often, the good old 6p14p and 6p3s were used. However, circuits with horizontal output pentodes - 6p45s, 6p44s and 6p41s - have repeatedly appeared on the Internet. I decided to stop at the latter, since despite the lower power than the 6p45, it does not have an inconvenient and dangerous pimp on top where the high-voltage anode wire is connected. Interest was further fueled by conflicting reviews on audiophile forums - from praise to complete denial of its sound parameters. As you know, it is better to collect it yourself, and then make a final conclusion. I took as a basis the circuit diagram of a single-ended amplifier by S. Sergeev, only slightly changing the ratings of the piping and the bias of the output stage.

The driver has the usual 6p14p in the output - here its role is secondary, pre-amplification. The output stage contains 6p41s with automatic bias, which has proven itself to be excellent for its simplicity and stability of lamp operating parameters. The only difficulty - a powerful resistor - was solved simply. Since a search in boxes with 10-watt green ceramic resistors did not produce results (everything is available except the required 450-680 Ohms), I had to solder a garland of three MLT-2s on a small scarf, 180x3 = 560 Ohms.

The cathode resistor of the second channel is also assembled on it. Since the estimated power is 2 watts, these 6 are quite enough. You would still have to think about how to attach 2 powerful tubular resistors.

Power to the ULF comes from the mains transformer, rectifier and inductor. Transformer TSSh-170 is from a tube TV; you can also install TS-160, TS-180 here. In general, anyone capable of providing 250-300 V 0.3 A anode and 6.3 V 3 A filament voltage. Rectifier diodes – IN4007, choke – Dr-0.1. It has 1000 turns of 0.25 mm wire (this is if you don’t find a ready-made one and wind it yourself or take a network transformer to replace it).

Despite the significant voltage and current in the output stage - about 0.06 A, I took the risk of installing the relatively weak TVZ-1, which is more appropriate in 6p14p amplifiers. As it turned out later, I did the right thing :)

It would not hurt to take a metal case for our single-ended ULF, as I always did before, but I decided to take a risk here too, using an unnecessary Chinese front speaker from a 6-channel computer amplifier. This number also went with a bang :)

We will gut the acoustic system, design the future location of the radio elements and cut out the necessary windows.

Naturally, the lamps should be on top; we install them on a metal base - a two-millimeter aluminum sheet, with cut-out round windows for the panels.

Then this sheet is covered with self-adhesive metallic color to match the main body. After gluing, the holes for the lamps are carefully cleared using a blade.

The lower part of the case is also reinforced with metal - so that the heavy network transformer does not fall out. It was also planned to install an electronic power filter on it, but in the end it was abandoned. The voltage at the power supply output is already not enough (only 260 V), so losing 20 V to the EF is a waste.

At the back we cut out a rectangular window for a textolite panel of sockets and connectors - network, audio input and audio output to speakers.

We also cover this panel with self-adhesive tape.

Then we insert all the contact elements and screw it to the pre-cut AC window.

Large electrolytic capacitors were installed on a single aluminum base. There are 4 of these dimensional electrolytes - three for the power supply filter and one for 300 uF 63 V, installed in the 6p41s cathode.

The case material, chipboard, turned out to be very easy to process, and electromagnetic interference from devices, which I was so afraid of, was absolutely inaudible. But we’ll talk about this in the second part of the article – assembling, configuring and testing the circuit.

Forum on ULF on lamps

• SE TUBE AMPLIFIER ON EL34
• TUBE FOR HOME AUDIO SYSTEM
• POCKET TUBE AMPLIFIER WITH BATTERY
• TUBE ULF ON 6F3P (6BM8, 6PL12, ECL82)

↑ Printed circuit boards included

In the files section you can download the project's printed circuit board drawings in *.lay format

Main board.

Master.

Loop.

Clean channel board.

Lead fee.

Filament power board.

↑ Amplifier parameters

The amplifier develops 30 W of undistorted sine wave power into an 8 ohm load.
The background level is minimal, it is practically inaudible when the input is short-circuited and the VOLUME and GAIN knobs are turned to the maximum (for the LEAD channel). That is, at the output of the amplifier, the background did not exceed 10-20 mV of the amplitude value.

The frequency responses of the CLEAN channel at various positions of the JAZZ / ROCK and DEEP switches and various positions of the TREBLE / MID / BASS tone controls, obtained using the MicroCap 8 simulator, are presented below.

Rock

Rock_Deep

Jazz

Jazz_Deep

↑ Amplifier settings

Setting up the amplifier comes down to setting the quiescent current of the output lamps in the range of 30-40 mA for each lamp using resistor R89 ​​and is selected according to the signal shape.
The absence of step-type distortion at power close to maximum indicates a normal quiescent current. I measure the quiescent current by simply connecting the tester to the break in the wire going to the anodes of the output lamps and the winding of the output transformer.

Resistor R91 is selected so that all relays used in channel switching operate reliably.

Resistor R52 is selected in such a way that the volume remains the same when switching channels (to taste).

Push-pull tube amplifier for 6P3S and 6N9S

Actually, the tube sound virus infiltrated me through a small article posted on this resource. Here she is, right here. Thanks to the author. The study of theory on this issue has begun, and not esoteric heresy from the Internet, but books by Tsykin, Gershunsky, Voishvillo and the like. Amateur radio magazines from the 60s are also interesting; I see a lot of modern know-how in them.

It was not possible to make an amplifier with my own hands, although I bought lamps, chokes, and transformers, because my father bought an amplifier from some radio amateur that was abandoned halfway, which never played... I had to change the phase inverter circuit and reduce the values ​​of the resistors (to reference values) in the circuit control grid of the output lamps to ground, since these lamps eventually locked and no current flowed through them, reducing the gain to zero.

The final version of the scheme is given below. The volume control is excluded as unnecessary. In principle, the scheme is simple and does not require any special explanation. The electrolyte in the cathode of the input tube is specially chosen with a small capacity in order to reduce the gain at low frequencies (I don’t like them) due to current feedback. The saw in the cathode (and anode circuit) was smoothed by installing a choke after the diode bridge. I struggled with self-excitation for the longest time at frequencies of 100 kHz and above. 4.7k resistors in front of the output lamp grid and ceramics that shunt the electrolytes in the anode supply from there. I also tried to ground the grid through a container, and put something like an RC filter there - it was no use. Until the signal cord from the computer to the amplifier was pulled out. All ultrasonic debris disappeared because it came from the sound card. I will have science for the future so that I don’t fight with windmills.

The AC hum dropped below the audibility threshold (if you do not put your head to the speaker) after setting the midpoint from the input lamp filament to ground, through a pair of 4.7k resistors

To be honest, the idea that captivated me about owning and hearing tube sound raised some doubts or concerns. I was worried about one question, namely, is the game worth the candle? Will I hear any difference? If you read the Internet, you get the impression that I will definitely hear. But you can also read there about how people’s bass comes off their speakers after wrapping the interconnect cable with three layers of electrical tape. Or they describe wonderful changes in sound from replacing a simple acoustic cable with a magic one at $300 per meter (with mandatory listening to the correct direction of connection and pre-warming the cable with the right music so that the electrons cut good trajectories in the conductor) and other muddiness.

However, what I heard completely met and even exceeded all my expectations. The sound has acquired detail. The acoustic guitar became like an acoustic guitar, the howling wind became howling wind, and the chirping birds in the background became chirping birds instead of the strange noise I took for distortion. Although I don’t know how to describe it in words, it needs to be heard. After listening to the composition from the lamp, I immediately repeated it with the Romantika 50U-220S amplifier and separately with the Microlab Solo-3 Mk2. The sound became muddy. It feels like the high frequencies were turned down by the tone block, but the subsequent increase in high frequencies does not correct the situation - it only adds all sorts of clicks, whistles and other noise from the high-frequency speakers.

I will not argue that the transistor is garbage, kills the soul, etc. and so on. I don’t have a perfect reference system for comparison; I think there is a transistor or integrated amplifier with the same detailed sound (the price will just be completely different). Moreover, I listened to music not on Hi-End speakers, but with SOYUZ 50AC-012. And in general, talking about killing sound with a transistor is absurd. My signal source is digital, the entire path down to one volt is semiconductor. Why bother with trifles, already in the studio, during the process of recording music, the signal could pass through 300-400 transistors (information from some article by Likhnitsky). If the sound has already died several times, then why should it be resurrected in the lamp?

Okay, I’ll put the chatter and thoughts aside. I'll add a couple more photos.

Feedback with me is possible here, in my journal, using the tag - sound - recordings of this focus.