DIY lamp amplifier designs. Tube audio power amplifier. The principle of assembly of tube amplifiers

Every novice radio amateur has heard or read about the superiority of tube sound-reproducing equipment compared to sound-reproducing equipment built on semiconductors. The continuing interest in the manufacture of structures using radio tubes prompted me to write this article, which will consider the main design criteria of this type amplifiers. So let's get started. First of all, it is necessary to formulate the first law of Hi-End technology: the sound signal must undergo as few transformations as possible and be amplified by as few stages as possible. To confirm this unshakable rule, the simplest linear sound amplification circuit (class A) in one clock is the best way.

In addition to all its ‘sound’ advantages, this circuit is suitable for mastering tube technology due to the simplicity of its assembly and the minimum number of parts. Here it is necessary to mention some features regarding the selection of components, assembly, setup and use of such devices. Tube amplifiers are rightly criticized for their 'fuzzy' bass. The reason for this is the increased output impedance of the tube amplifier, so professionals advise calculating and adjusting the speakers for a specific tube amplifier. Some specialists even make complex output transformers, where each output winding drives its own separate speaker in speaker system! To reduce harmonic distortion and eliminate acoustic background, the method of sectional layer-by-layer winding of both network and output transformers is used (for example, placing primary winding between the halves of the secondary). It is considered advisable to use toroidal transformers (everyone is familiar with their advantages), but making them at home is quite difficult - it requires skill and patience.

This leads to the second immutable law of Hi-End technology: you need to pay as much attention as possible to the manufacture of transformers - the sound quality of your home-made unit depends 90 percent on this. A very important issue is the construction of the amplifier power supply. Personally, I would not recommend using rectifiers based on semiconductor diodes - they greatly weaken the sound. The most effective solution, in my opinion, is the use of kenotron lamps with an LC filter chain. The advantages of this circuit are undeniable - as the cathodes of the kenotron warm up, voltages are applied to the amplifier circuit gradually (and not simultaneously, as when using semiconductors, where it would be necessary to supplement the circuit with an anode voltage relay switch in order to increase the service life of electronic tubes). The most common kenotron available to the DIYer is the 5Ts4S type lamp.

The use of rectifiers and filters in the filament circuits of lamps is also not advisable - in addition to the risk of signal degradation associated with the use of semiconductors, some lamps categorically refuse to ‘work well’ if their filament circuit is powered by constant voltage! In addition, the amplifier circuit must be supplemented with an interference suppression network filter (see the article Homemade filter for lamp equipment), which will rid the unit of a lot of low-frequency/high-frequency interference from the household AC network. You should also pay attention to the selection of passive components for a tube amplifier. It is advisable to use only metal film resistors, MLT type, with minimal deviation from the nominal value. And although not every radio amateur will be able to get, for example, five-watt film resistors (these can only be purchased on occasion, and some have never even seen them!) one should refuse (to the extent possible) from using wirewound resistors, both domestic and imported.

You should also be very critical about the choice of capacitors - they are best suited with a polypropylene dielectric, film and polycarbonate,

and although not everyone will be able to afford to purchase specialized capacitors for Hi-End assemblies, all of them should be checked before installation in the circuit for leakage, internal resistance, etc.

At worst, you can use capacitors with a paper dielectric of the MBM type and mica type KSO-1. The most 'musical' and common lamps for assembly single-ended amplifier, according to many experts, are 6N23PEV lamps

and 6P14P. The letters E or EB in the designation are an indicator of more High Quality performance of the lamp.

There are many designs of amplifiers based on these tubes on the Internet, so circuit diagrams I won’t give them, I think I should just give their passport details in the attached archive.

You should also (to the extent possible) avoid using any sound correction circuits when making a tube amplifier. If this condition is not met, the most reliable potentiometers from Alps should be used.

or Noble - breakdown or break of the adjustment resistor is fraught with very serious consequences, in addition, the use of low-quality potentiometers can introduce noticeable distortions into the playback signal. For the manufacture of the amplifier chassis, a material that has been tested over the years is used - aluminum (due to its strength and ease of processing at home). All connections when mounting an amplifier on lamps are made directly on the lamp sockets. The panels should also be selected with particular pickiness - it is better if they are ceramic panels with reliable collet clamps for the base contacts of the lamps. During assembly, it is better to use silver-plated or tinned wiring; The same applies to the solder used - high-temperature solder with a high silver content is ideal. It is advisable to make all detachable connections (input/output) using the most reliable connectors possible; it is even better to use terminal blocks with a ‘nut’ fastening. The speakers should be connected to the amplifier with conductors (with a cross-section of 0.75 kV/mm and above) made of copper (and in no case Chinese bimetal). A few words about acoustics for a tube amplifier. Since it is impossible to achieve high amplifier power when implementing a single-ended circuit, it is advisable to use high-quality speakers of increased sensitivity assembled using a horn circuit.

Another nuance of using tube amplifiers, professionals say, is the use of a separate power connection line for the amplifier complex (directly from the switchboard) with a conductor of at least 6 square millimeters (consider the welding cable). My personal opinion is that this is an exaggeration. I think it will be quite reliable to use standard electrical wiring (2.5 kV/mm) and a socket with reliably spring-loaded contacts, in order to avoid chatter and interference when the power circuits are unreliably connected. I hope that this article, which briefly outlines the main criteria for the design and assembly of tube sound amplification equipment, will serve as a reliable reminder for a radio amateur who has decided to assemble a device of this category for the first time!

The first successful tube experience in my amateur radio life was this amplifier using 6N2P+6P14 tubes, 5 Watts in each channel. I consider the scheme suitable for repetition by beginners, for example, for near-computer use.
It all started with the fact that they gave me a package of various lamps and a TAN-46 transformer as unnecessary.

As a case, it was decided to take an empty box from a Soviet legend - the Radiotekhnika U-101 amplifier. I’ll make a reservation right away that I didn’t tear anything out of the amp with my own hands, it was “the chapel that was destroyed” before I did. My dad assembled one out of two faulty amplifiers, when it was simply impossible to get parts for repairs, and I was still walking under the table. Since then the corps has been waiting in the wings.

Amplifier and power supply circuit

The heart of the power supply was the aforementioned TAN-46. I assembled two 125V windings and got 250V AC. Load capacity 0.118mA. I calculated the anode current of all four lamps using maximum value, received 0.1184 mA. Suitable, so all the lamps at once will not consume the maximum current. And if you remember about the “Soviet safety margin” of transformers, you can generally sleep peacefully.

Assembly

The lamp filaments were powered directly from the secondary windings of the transformer with a voltage of 6.3V. Organize the heat DC, in those days, I didn’t even have it in my thoughts.

I soldered the elements onto the breadboard and placed it in the middle section of the case. She fit in there like a glove and even pressed herself with the original wire clamps. A power transformer and two TV-3Sh output transformers were installed in the rear part of the case without modification. In search of output transformers, I had to go around to all my friends and acquaintances with the question, did you happen to have a tube TV lying around?

I modified the top cover: I drilled four holes in the metal center for the PL-9 lamp sockets, and in the plywood part I cut a hole for the TAN-46 transformer; its dimensions did not allow covering the structure with a lid. I glued these two parts together and painted them black.

I screwed the lamp sockets to the lid, and screwed the lid itself to the body. I installed gold knobs on the potentiometers. As you may have noticed, only two potentiometers are used, the rest I installed for beauty.

Total

As you know, in amateur radio circles, amplifier mock-ups often remain just mock-ups. It’s easy to quickly assemble a model “on plywood”, but you often don’t have time to build a beautiful building! Difficult, expensive, lazy...

With this article I want to make my contribution to the “development” of amateur designs. So, a tube headphone amplifier housing from scratch in a day or two! The basis was taken as published on the portal. It doesn't matter. This way you can assemble a housing for any design.
We take an aluminum corner as a basis (I used a corner with a cross section of 20x20 mm). It is better that its thickness is at least one and a half millimeters. And carefully cut the blanks for the future body.

We take a sheet of duralumin and cut out blanks for the top and bottom covers of the future case:

We press the cut sheet to the body with clamps (sorry, I forgot to take a photo) and drill holes for fastening both in the lid/bottom and in the corners of the frame. The fact is that the holes are made first with a drill of a smaller diameter - for threads, and only then with a larger one - for screws, separately in the housing covers. If you drill separately, nothing good will come of it. The holes just won't line up!
Take it for general rule Drill all through connecting holes immediately in the “package”.

The covers should protrude slightly beyond the boundaries of the housing. Excess in place can be easily removed with a file or grinder.

We cut wooden slats for the “sides” of the amplifier. Wooden trims (also known as door trims) are perfect as a material.

This is where the right tool is a big advantage. I use the following set: an accurate disc miter box and a very high-quality cross-cut saw Kataba Speed ​​Saw 265. The cut starts very accurately, the blade does not “walk”, the angle is maintained very well during leisurely sawing.

In addition to the hacksaw and miter box, the set includes a square and a test hacksaw blade without teeth for shooting.

Made In Japan. The clever layout is clearly visible - the teeth are sharpened inward.

The amplifier itself was assembled on a small duralumin chassis connected to the top cover with screws and 5-7 mm racks. This is done in order to hide the lamp panels. Naturally, all the holes in the chassis and top cover were drilled in advance in a “package”. I wrote about this above.

Build process:

The parts of the rectifier and anode voltage doubler are attached to the bottom cover. Lamp filaments are powered by separate windings alternating voltage and “rested” into the ground with a pair of 150 Ohm resistors.

Test run:

As a rectifier - a diode bridge, and as filters - 2 capacitors from a computer power supply, 200 volts 470 uF connected in series, the result is an output of 315 volts on the capacitors. The whole thing is connected to the plus through a 2.7 kOhm resistor in the power supply gap. The power supply to the anodes is approximately 250 volts DC. We shunt the power filter capacitors with a 200 kOhm resistor so that there is something to discharge them after disconnecting the device from the network.

The power supply is made in a separate case from the old tube TV. The tube amplifier itself is made in a casing from a Soviet radio tape recorder, its casing is thick and just the right size.

Sockets for lamps can be picked out from any lamp equipment - they are all standard. We make a large hole using small ones drilled in a circle. We clean the edges with a round file.

I made a speaker based on a 5-gauge paper speaker, with a rated power of 5 W, the base itself is made of boards, rear end- plywood, and the speaker itself on the front panel is mounted on two compressed sheets of cardboard.

I made the legs for all the blocks by gluing pieces of double-sided tape to the body so as not to scratch the surface of the table. See the video below about assembling a simple ULF on lamps:

A 3.5 mm metal plug, “female” type, is soldered to the input. The conductor that goes through the audio input must be well shielded.

I removed the volume control, since it only produces unnecessary noise, and in the sound source itself (in my case DVD player) it’s much more convenient to regulate it from the remote control!

Don’t forget to put a 200-500 kOhm resistor on the ground at the input, and if you are making a regulator, then use a high-resistance one, I tried it at 1 mOhm and it turned out to be the best.

Perhaps the design will not seem particularly serious to some, but keep in mind that this is my first step in mastering tube ULFs. The next amplifiers will be more impressive. Comrade was with you. Redmoon.

Discuss the article SIMPLE TUBE AMPLIFIER

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

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

How to choose a tube amplifier circuit

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

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

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

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

The principle of assembly of tube amplifiers

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

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

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

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

Pre-stage tubes

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

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

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

Retro components

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

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

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

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

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

Single-ended tube audio power amplifier

The presented tube amplifier circuit consists of three separate modules:

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

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

Electronic components of the preamplifier

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

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

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

Setting up a tube amplifier

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

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

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

Amplifier power supply

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

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

Power amplifier assembly sequence

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

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