How to assemble a tube amplifier. DIY tube amplifier: step by step instructions, diagrams, materials

I was contacted by a person whom I once helped in a search for radio tubes. This time, he needed help in repairing the amplifier, which he assembled on these tubes: a strong hum appeared in one channel, which he could not overcome in any way.

Here I need to say a few words about the customer himself - this is a brutal uncle of a biker look, with a thick black beard and tattoos, and at the same time a kind-hearted man. His occupation matches his appearance - motorcycle repair. In electronics, he, in his own words, understands nothing. Everyone would not "understand" that they can assemble their own tube amplifiers, but oh well)
I agreed to help him, and soon he brought me this miracle:

The case for the amplifier was welded from 2mm steel plate, which was then additionally aged and covered with copper. Fortunately, there are still photos of the workflow, so I'll share them with permission:

All work was done by hand using a grinder, drill, files and, of course, a welding machine.

The design bizarrely combines modern elements and parts from Soviet radio engineering.

I really liked the textured finish of the case, and I even seriously thought about using something like that in my own projects.

All in all, the amplifier was left to me with a request to have it repaired as soon as possible. I connected it to the speakers and made sure there was a strong hum in one channel. As you know, electronics is the science of contacts, so for sure either something somewhere has been sealed off, or, on the contrary, closed. This can be fixed pretty quickly, I thought naively.

When I first looked into the "basement", at first glance, everything looked good - at least for an amplifier made by an absolute beginner. The author simply took and put inside two boards of low-frequency amplifiers from the Ural-112 radio.

But since the location of the lamps and transformers did not suit him, he evaporated them and diligently increased all the wiring connections.

Unfortunately, lamp technology does not tolerate such an installation: long wires, repeatedly intertwining and crossing each other, collect all imaginable noise and interference. In addition, the author used a monochrome MGTF wire, and it was almost impossible to figure out what was going where. And there was no point in leaving the motherboards: their only advantage, which is that they can be put “as is” and save time and effort, was lost, and only shortcomings remained.

For example, outdated selenium rectifiers and huge resistors of the BC type, which were used only in the power supply circuit of the high-frequency radio unit (R5, R1 and R8), were in vain in the power section. But the resistive divider R3 – R4, which was supposed to supply a small positive voltage to the midpoint of the filament winding to reduce the noise level, was lost during the transfer.

It should be noted that this "not versed in electronics" person himself (albeit according to a ready-made scheme) unsoldered the display unit on lamps of the "magic eye" type, and even with a separate amplifier on a 6N2P lamp, which made it independent of the output level volume. True, in this case, huge 2-watt resistors were used (although 0.25-watt resistors would be enough for the eyes) - he put them according to the principle "many is not enough", so that there would definitely not be overheating. Here is such an amazing combination of ingenuity, straight hands and, moreover, a complete lack of experience, leading to a little curious, but still impressive results.

Acting on a whim, the author made two channels of the amplifier completely mirrored - each with its own power transformer. This also turned out to be redundant, since it was no longer necessary to power the lamps responsible for radio reception. The second transformer only interfered, and even hummed strongly, because its plates loosened from time to time, and the design did not allow them to be reliably pulled together.

In general, I realized that no quick repair it doesn't smell, and the amplifier needs to be completely redone. The situation was complicated by the fact that in just a couple of days I had to fly away on vacation. As a result, I soldered the last details at night right in front of the customer, and the next morning, having slept a little, I was already rushing to the airport) But everything turned out as it should, and the customer was pleased with the pleasant sound of the amplifier and the absence of noise. And only later I realized that in my haste I completely forgot about photographing the work process.

There is, however, a frame in which I use a battery and a microammeter to determine the direction of the power transformer windings.

In fact, I had to work hard. After all, I, in fact, had to do double work: first disassemble the amplifier to zero, and then reassemble it, but already correctly. 95% of radio components in the process were replaced with modern ones. Only the electrolytes remained in the power supply - their polished cases were an element of the external design. They were well preserved, so that their total capacity was sufficient for the background alternating current was not picked up by the ear at a distance of 20 cm from the speaker.

When working, I followed the basic rules of hinged "lamp" mounting - minimizing (within reasonable limits) the length of the conductors, spacing the signal and supply lines in space, mutually perpendicular orientation of the power and output transformers, shielding, avoiding ground loops, etc.

On vacation, I had already begun to slowly forget about this project, when suddenly the customer sent me photographs showing something very interesting:

Taking advantage of the lack of an extra power transformer, he made a new two-tier casing for the amplifier.

Severe tube amplifier tube amplifier, homemade products, modding, Alcatraz, equipment repair, long-post
It was no coincidence that the square holes appeared in it: it was decided to stylize the building as the building of the Alcatraz prison! Well, what is Alcatraz without a lighthouse?

As a result, it turned out like this:

The lighthouse is removable and magnetically attached. And the light in it not only lights up, but shows whether the built-in Bluetooth module, which is one of the possible sources signal for the amplifier.

This is how the ability to work with metal and the author's rich imagination, combined with my modest knowledge of lamp technology, led to the birth of a very unusual and functional device... I think "The Rock" would be a good name for it.

All work was done by hand using a grinder, drill, files and, of course, a welding machine.

The design bizarrely combines modern elements and parts from Soviet radio engineering.

I really liked the textured finish of the case, and I even seriously thought about using something like that in my own projects.

But since the location of the lamps and transformers did not suit him, he evaporated them and diligently increased all the wiring connections.

For example, outdated selenium rectifiers and huge resistors of the BC type, which were used only in the power supply circuit of the high-frequency radio unit (R5, R1 and R8), were in vain in the power section. But the resistive divider R3-R4, which was supposed to supply a small positive voltage to the midpoint of the filament winding to reduce the noise level, was lost during the transfer.

In general, I realized that there is no smell of quick repairs here, and the amplifier needs to be completely redone. The situation was complicated by the fact that in just a couple of days I had to fly away on vacation. As a result, I soldered the last details at night right in front of the customer, and the next morning, having slept a little, I was already rushing to the airport) But everything turned out as it should, and the customer was pleased with the pleasant sound of the amplifier and the absence of noise. And only later I realized that in my haste I completely forgot about photographing the work process.

There is, however, a frame in which I use a battery and a microammeter to determine the direction of the power transformer windings.

In fact, I had to work hard. After all, I, in fact, had to do double work: first disassemble the amplifier to zero, and then reassemble it, but already correctly. 95% of radio components in the process were replaced with modern ones. Only the electrolytes remained in the power supply - their polished cases were an element of the external design. They were well preserved, so that their total capacity was sufficient for the ac background not to be picked up by the ear at a distance of 20 cm from the speaker.

On vacation, I had already begun to slowly forget about this project, when suddenly the customer sent me photographs showing something very interesting:

Taking advantage of the lack of an extra power transformer, he made a new two-tier casing for the amplifier.

As a result, it turned out like this:

The lighthouse is removable and magnetically attached. And the light in it not only lights up, but indicates whether the built-in Bluetooth module, which is one of the possible signal sources for the amplifier, is turned on.

In the article, you will learn how to make do-it-yourself tube amplifiers from scrap materials. It's no secret that tube sound- the most beautiful, his fans will exist at all times, despite the fact that the market is full of large quantity proposals for small-sized equipment on transistors and microcircuits. Consider in more detail what you should consider when making a tube amplifier.

Nutrition is the main difficulty

Yes, it is with power that problems can arise, since you need two values alternating voltage: 6.3 V for supplying filaments and from 150 V for lamp anodes. The very first thing you need to find out for yourself is the power of the future structure. The power of the transformer for the power supply depends on this. Please note that the transformer must have three windings. Without such power, you can not make tube

In addition to the aforementioned secondary ones, there must also be a network (primary) one. It must contain so many turns for the transformer to work in normal mode. And even with a significant load (and power surges up to 250 V), the winding should not overheat. Of course, the dimensions of the power supply will be rather big due to large sizes transformer.

Rectifier

You will need to make a rectifier to get at least +150 Volts DC at the output. To do this, you need to use a bridge circuit for connecting diodes. D226 diodes can be used in the design of the power supply. If you need to make high reliability, then use D219 (they have a maximum operating current of 10 Amperes). If you are making tube amplifiers with your own hands, then follow the safety rules.

Diode assemblies work well in power supplies. You only need to choose those that are capable of functioning normally at voltages up to 300 volts. Pay particular attention to filtering the DC output voltage - install 3-4 electrolytic capacitors connected in parallel. The capacity of each must be at least 50 μF, the supply voltage is over 300 V.

Lamp circuit

So, now closer to the scheme itself. If you are making a tube guitar amplifier with your own hands, or for playing music, you need to understand that the most important thing is safety and reliability. The most common circuits contain one or two preamplifier stages and one power amplifier stage. The preliminary ones are built on triodes. Since there are radio tubes that have two triodes in one base, you can save a little space during installation.

And now about what elements the tube amplifiers contain. You will have to assemble everything with your own hands into a single structure. For a lamp in a pre-amplifier, it is best to use 6N2P, 6N23P, 6N1P. Moreover, despite the fact that all these lamps are analogs to each other, the 6N23P sounds much nicer. This lamp can be found in the PTC block (switch television channels) old black-and-white TV sets such as "Record", "Spring-308", etc.

Final amplifier stage

As an output lamp, 6P14P, 6P3S, G-807 are usually used. And the first will be the smallest, but the last two are very impressive in size. And the G-807 has an anode in the upper part of the cylinder. Please note that in tube ULFs it is imperative to use a transformer to connect acoustics. Without such a matching transformer, you cannot make a tube amplifier with your own hands.

Perfectly work as output transformers TVK, used in vertical scanning. Its primary winding is connected between the plus of the power supply and the anode of the output lamp. A capacitor is connected in parallel to the windings. Moreover, it is very important to choose the right one! First, it must be paper (such as MBM). Secondly, its capacitance must be at least 3300 pF. Do not use electrolytic or ceramic.

Adjustments and stereo sound

It will be very easy to make stereo sound. It is enough just to make two identical amplifiers. You can find a stereophonic tube amplifier in the old Soviet technique. You can repeat the design with your own hands. But you need to take into account some features:

connects directly to the amplifier input. which is used for it, you need to choose such that there are two elements on the axis in one case. In other words, when you rotate the knob, the resistance of two resistors changes at once.
Similar requirements for the frequency regulator. It is included in the anode circuit of the first triode of the preamplifier.

Amplifier housing

If you are making a tube guitar amplifier with your own hands, then it makes sense to use a metal case. He will not be afraid of blows and other minor shocks. But if you are making an amplifier for use at home, for example, to connect to a player, a computer, then it is wiser to use a wooden case. But it must be taken into account that it is advisable to fasten the power transformer to the case with rubber gaskets. With their help, vibrations are reduced.

Much depends on what the tube amplifier will be. With their own hands, many craftsmen make cases from sheet aluminum. If even small vibrations are applied to the lamp, its mesh will begin to vibrate. And these vibrations will begin to intensify, and the result is a buzz in the speakers. You also need to make a common bus, which should pass near all the lamps that make up the structure. All wires, through which the signal goes, must be shielded as much as possible - this will get rid of various kinds of interference.

Circuits with transistors

And another interesting design is tube-transistor amplifiers. You can make these with your own hands literally in the evening. But lamp structures, as a rule, are made by hinged installation. It turns out to be the most convenient and simple. And in case transistors are used, you need to use printed wiring. In addition, a voltage of 9 or 12 volts is required to power the transistor stages. Moreover, transistors are used only to build a preliminary amplification stage. In other words, you only have one tube left - in the output stage (or two, if we are talking about a stereo version).

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

Unique apparatus

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

Selecting circuits for assembly

The preamplifier is fairly easy to assemble. For it, you can choose any suitable circuit and start assembling. Another case is the output stage, that is, the power amplifier. With him, as a rule, many different questions arise. The output stage has several types of assembly and operating modes.

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

In a single-ended circuit, only two parts are sufficient for good operation of the device: a power amplifier and a pre-amplifier. The push-pull model already uses a bass-reflex amplifier or driver.

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

If you are a connoisseur of "tube" sound, then you must understand that you need to use a rectifier, which is produced on a kenotron, to achieve this sound. In this case, you cannot use semiconductor parts.

When developing a Hi-End tube amplifier, you do not need to use complex circuits. If you need to sound a small enough room, then you can use a simple one-cycle design, which is easier to make and set up.

DIY Hi-End tube amplifier

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

In Hi-End, mounting lugs and strips are used. They are used as additional points. This assembly is called hinged. You will also need to unsolder the resistors and capacitors that are found on the lamp panels. It is highly discouraged to use printed circuit boards and collect the conductors so that parallel lines are obtained. This will make the assembly look chaotic.

Eliminate interference

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

The type of connection is star, in which all "earth" conductors are connected to one point.
The second way is to run a thick copper bus bar. It is necessary to unsolder the corresponding elements on it.

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

To make the heating circuit of the radio tubes, you need to use a twisted wire.
Lamps used in a preamplifier must be covered with earthed caps.
It is also necessary to ground the housings with variable resistors.

If you want to feed the incandescence of the pre-amp tubes, you can use a constant current. Unfortunately, this requires the connection of an additional unit. The rectifier will violate Hi-End tube amplifier standards as it is a semiconductor device that we will not be using.

Transformers

Another important point- the use of various transformers. As a rule, power and output are used, which must be connected perpendicularly. This way you can reduce the level of low-frequency background. Transformers should be placed in grounded housings. It must be remembered that the cores of each of the transformers must also be grounded. It is not necessary to use it when you install the devices, so that additional problems do not arise. Of course, these are not all the features associated with the installation. There are quite a few of them, and it will not be possible to consider everything. When set to Hi-End (tube amplifier), you cannot use new element bases... They are now used to connect transistors and integrated circuits. But in our case, they will not work.

Resistors

A quality Hi-End tube amplifier is a retro device. Of course, the parts for assembling it must be appropriate. Instead of a resistor, a carbon and wire element may be suitable. If you do not spare funds for the development of this device, you should use precision resistors, which are quite expensive. Otherwise, MLT models are applicable. This is a pretty good element, as evidenced by the reviews.

Hi-End tube amplifiers are also applicable with VS resistors. They were made about 65 years ago. Finding such an element is quite simple, you just need to walk through the radio market. If you use a resistor with a power of more than 4 watts, you need to choose wire enamelled elements.

Capacitors

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

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

Single-ended amplifier

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

power unit;
terminal stage;
a pre-amplifier in which you can adjust the tone.

Assembly

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

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

The constituents

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

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

To set up and check the functionality of the assembled device, you must use a multimeter. If you want to get more accurate values, then you should use a sound generator with an oscilloscope. When you have taken the appropriate devices, you can proceed to the setup. At the cathode L1, we indicate a voltage of about 1.4 Volts, this can be done if you use the resistor R3. The output lamp current must be specified as 60 mA. To make a resistor R8, it is necessary to install a pair of MLT-2 resistors in parallel. Other resistors can be of different types. A rather important component should be noted - the blocking capacitor C3. It was not mentioned for nothing, since this capacitor has a strong influence on the sound of the device. Therefore, it is better to use a proprietary radio element. Other elements C5 and C6 are film capacitors. They allow you to increase the quality of transmission of various frequencies.

The power supply unit built on the 5TS3S kenotron is worth finding. It complies with all the rules for constructing the device. A homemade Hi-End tube power amplifier will have quality sound if you find given element... Of course, otherwise it is worth looking for an alternative. In this case, you can use 2 diodes.

For the Hi-End tube amplifier, you can use the corresponding transformer that was used in the old tube technology.

Conclusion

To make a Hi-End tube amplifier with your own hands, you must perform all the steps consistently and carefully. To begin with, a power supply unit with an amplifier is connected. If you tune these devices correctly, you can mount a preamplifier. Also, using the appropriate technique, you can check all the elements in order to prevent breakage. After assembling all the elements together, you can begin to design the device. Plywood can work well for the case. To create a standard model, it is necessary to place radio tubes and transformers on top, and regulators can already be mounted on the front wall. With the help of them, you can amplify the tone and see the power indicator.

A simple tube audio amplifier with your own hands or feel the warmth of tube sound

I no longer remember how and when this strange idea settled in my head - to assemble a tube amplifier. Why, too, is not entirely clear - I am not a music lover, I have been ill with home theaters for a long time and quickly, the floor-standing speakers Wharfedale Diamond 8.4 remained in memory of this time, in recent years they were used exclusively as a decorative stand for flowers. Be that as it may, the thought so deeply settled in my head that a leisurely study of specialized resources began, reading forums, searching for circuits of tube amplifiers "for dummies", etc. etc. Lack of any experience of communicating with lamp technology (the most modern gadget(which I remember is a b / w TV in a student hostel in the early 90s of the last century) scared and attracted at the same time.

A sluggish search could go on indefinitely, if one day a wonderful resource was not discovered - http://tubelab.com/. I opted for a Tube Lab Simple Single End (SSE) single-ended amplifier, ideally suited to my interests, namely: a simple amplifier for beginners with a minimum of components, no adjustments, at the same time quite versatile and, judging by the reviews, has proven itself very well. The order of the board was made on the website (sent anywhere except Russia and Italy), payment via Paypal, short correspondence with the developer, fairly fast delivery of two boards (In addition to SSE, a board was also ordered for the advanced version of Tublab SE - so to speak "for growth") ... It was decided to order the components via e-bay, not quickly, but reliably and inexpensively - delivery times were compensated for by convenience (receipt by mail, leisurely search while sitting at a computer). The process took quite a long time, but I was not particularly in a hurry (almost 2 years passed from the moment of ordering the boards to the moment of successful inclusion).

The first received components

It makes no sense to describe the process of assembling the amplifier board, detailed instructions with pictures is on the project website. I was especially pleased with the disclaimer disclaimer:

We are not responsible for injury, accidents, acts of random stupidity, burning your house down, exploding parts, and other undesired actions (all of which are possible) resulting from the use of ANY information contained herein.

Some recommendations received in the process of studying the materials.
Never install electrolytes "all the way"; there should be a small gap between them and the board. The fact is that when soldering, the leg heats up and lengthens, and when it cools, it shortens, and, with a tight fit, it may simply fall off from the lining. Considering that in a tube amplifier the heating-cooling process occurs regularly, it is worth paying attention to this point.
Weekend chassis and power transformers positioning perpendicularly to reduce mutual influence.
Isolate the audio input connectors from the chassis to avoid ground loops on the signal lines. If the wire is shielded, then the shield should be grounded only on one side.
Order spare parts with a stock in order to avoid delays in logistics and save on delivery.
And most importantly, be careful when shopping for components on ebay (more on that later).

One of the problems that I had to face was the choice of transformers (power and output) - it is quite difficult to buy a transformer with the required voltages, if the 110-volt version is usually available from American retailers, then a 220V transformer must be ordered from the manufacturer and wait 45-60 days. In addition, they are quite heavy and the cost of shipping from the US almost doubles the cost of an order. Fortunately, a suitable version (Hammond 374BX) was found in Germany, which made it possible to significantly save on shipping and, along the way, order a choke (inductance) for use in the output filter of the power supply. The first mistake - when ordering an inductance, I selected the resistance, completely forgetting about the current, as a result I got a coil with a current limitation of 100ma instead of the minimum required 170ma, I had to go back to a simpler and lower-quality version with an RC filter and buy a suitable wirewound resistor, change the resistor on the reel, if the desire arises, you can at any time. It was easier with the output transformers, only Transcendar had adequate delivery times, the TT-119 model came up in all respects.

Finally, the moment came when all the components were received, there was free time and nothing prevented me from seeing how all this would work. In violation of all safety regulations, all connections were made directly on the table in front of the monitor.

An old LG-P500 was invited to act as a signal source, speakers from music center it took some red duct tape and a little courage. Taadaaaam - switching on took place, nothing exploded, the lamps lit up with a beautiful orange light ... and silence, more precisely, if you bring your ear to the speaker, you could even hear music against the background of the noise, but it was not at all the "warm tube" sound that I had hoped for hear.

The first thing I decided to check was the voltage at the output of the rectifier, and was immediately unpleasantly surprised, instead of the expected 375V x √2-27V = 503.33V (voltage on the secondary winding multiplied by the root of 2 minus the drop on the lamp), I saw almost 550V at the output of the rectifier and, accordingly, 525V B + (anode voltage). There was no desire to test electrolytes for endurance (they are designed for 500V), so I had to turn off the power. After checking the mains voltage, I was once again surprised - it turned out to be more than 240V (further polling of neighbors confirmed that this is the case for everyone). Fortunately, the transformer can be re-wired for this voltage. At the second turn-on, the voltage returned to normal, but the speakers were still silent, further testing revealed the absence of anode voltage on the input triode, which, in my opinion, indicated a malfunction of the only semiconductor device- regulated current source IXIS10M45.

Deciding that the problem was due to overvoltage and / or a Chinese ebay seller, I ordered a new pair of IXIS10M45 from England, it seemed more reliable and faster. I must say that the next inclusion was completed absolutely similar to the first and second, although the new parts looked completely different, they refused to work in the same way. Here I already started to worry, since both channels behaved completely identical, and the voltage on the 12AT7 anodes was completely absent. Since in this circuit, apart from the lamp itself, the current regulator and a priori working small things, there was nothing else, suspicion fell on the lamp. The auction on ebay made it possible to buy ECC81 (the European analogue of the American 12AT7) at a very low cost, and at the same time the next batch of IXYS 10M45 (again, the Chinese seller took it with a margin just in case). The third batch of 10M45 looked (and rang) exactly the same as the second, for the purity of the experiment, I immediately replaced the lamp and IXYS, disconnected all unnecessary (second stage) and for the fourth time did not find anything on the anode of the first triode.

A complete failure, the mind refused to understand how this could be. On a breadboard, I assembled a simple circuit with an LED and an adjustable current source (I used an untouched one from the third batch), powered it from a laptop power supply - and IT WASN'T WORKING !!!

At that moment, the thought of a universal conspiracy began to haunt me, even what was supposed to work did not work ... and again I decided to order problematic microcircuits, only through a trusted seller (Digikey). And once again, difficulties arose even where they should not have been. The first problem that arose (in Digikey, the minimum shipping cost to my region was $ 75, even for a $ 5 order). This problem was solved with the help of an American intermediary, but the second one came to light after placing the order - a letter came to my email with a request to confirm that I was not a terrorist to fill out the BIS711 form (who is interested in goo.gl/VAkDYB). I ordered ordinary radio parts to an American address, why I need to fill out this form when buying ordinary radio parts, I still don't understand. Having indicated my name, my name and home address in all fields, namely: I am the end user, I am the official representative of the end user, I am the buyer, I am the exporter and indicated that I am an individual, sent the completed form to Digikey, and the very next day I received an order confirmation and tracking for the parcel.

Another batch appearance differed from all previous ones, which inspired some optimism (picture below)

The test on the breadboard made me happy, the LED happily changed its brightness depending on the resistance of the control resistor. Five minutes to replace a part on the board ...

... another switch on and MUSIC began to sound from the speakers.

As it turned out in the process of communication on specialized forums, counterfeit radio components on ebay are becoming a big problem. Here's what the Diyaudio moderators write
- Fake parts are a real plague by now. No small chance we all get a share of those when fishing for a quick small purchase.
- I never buy semi-conductors or electrolytic capacitors on eBay for this reason.

As a result, I got paid, regained my self-esteem, and became disillusioned with Ebay. On the hastily the case was made, as intended as a mock-up for testing layouts, but unexpectedly liked.

V currently the amplifier works in conjunction with the Raspberry Pi & Volumio (as a source), the sound is really very pleasant and really warm (+ 65C). There are plans to improve the case, overcome a little interfering hum, build in a USB DAC (there will be a tube sound card), it is possible to add remote control... If you are interested, I will describe the manufacturing process of the case, as well as tell you about the problems identified and ways to eliminate them.

Scheme and arrangement of elements (it is difficult to find it on the site, used to mark holes on the case).