I want to tell you about my history of repair and modernization of the Radiotekhnika U-101-stereo amplifier. It seems to be a completely ordinary amplifier from the USSR, but there is some inexplicable attraction in it ( for me personally), which is difficult to explain.
How to describe the feelings when you meet a completely unfamiliar girl, cross your eyes, and then for a long time her eyes and the silhouette do not leave your memory? ... I liked it, beautiful, but your destinies are not destined to intertwine.
When I first saw / heard Radio Engineering I can’t even remember. But it stuck in my memory, and not just a wild desire to buy and listen, no - just a pleasant image. And then the other day the thought materialized and fate gave me a gift RT 101. Tired, tortured by everyday life and lack of attention.
If only my wife didn’t read these lines, otherwise she’ll get jealous and declare crazy
:love: I can not put up with malfunctions and a terrible technical condition, I have no peace. Therefore, instead of flowers and sweets for my wife, I regularly buy capacitors, microcircuits, resistors, and so on ...
I decided to bring RT back to life. To begin with, the following was to be overcome:
1. Transformer hum.
2. The same terrible rumble in the speakers.
3. Clap when turned on and some terrible sound when turned off.
4. Inoperative signal indicator.
5. Rustling regulators.
The first step was to replace all the electrolytic capacitors. Everything is according to native ratings, the only thing in the power supply unit is slightly increased capacitance: 2x2200+ 2x4700 uF to power the final stage (C3, C4, C8, C9 in the diagram). Diodes KD209A are replaced by "ultrafast" UF4007.
I will say right away - this operation almost eliminated the first three points of problems.
It was not possible to revive the indicator by simply changing the capacitors, but I wanted so little bloodshed ... It continued to show the full scale, not reacting to anything. In the course of finding out the reasons on the forum, we came to the conclusion ( possibly false) that the K161PP2 chip failed. Finding one, you know, is not easy. Easier completely indicator.
The world is not without good people (believe in it, do good yourself and the result will not keep you waiting long) and the indicator, along with the ULF-P of the latest revision, the one on the same chip, was given to me by the broadest soul of the man Vasily (Skif on Vegalab). For which he bows low and many thanks! True, the functionality of the modules was questionable.
In the acquired indicator, I had to replace the tuning resistors, which were filled with nail polish and became unusable. Earned indication of one channel!!! But we have a stereo ... For a long time I did not suffer, but immediately decided to replace K157UD2. The operation was a success and that unforgettable green spark appeared in the eyes of RT again.
Further more.
The sound after restoration was mesmerizing with bass. It would seem that 2x 20 W, but such a bass that the windows tremble, the plasterboard partition in the kitchen vibrates, and in the evening, while watching a movie at a volume level below average, the neighbor called downstairs and in a sweet, restrained voice asked to turn down the volume.
But happiness did not last long. Having read strangers opinions and feedback on how much a single-chip pre sounds better, less distortion, etc., I decided to change my native one. ( For the sake of the reliability of the article, I will inform you that it was replaced at the stage of work with the indicator. Prior to this, the ULF-P of the old revision was listened to for a couple of weeks.) And at first I did hear ( or wanted to hear) all these advantages: “high detail”, “clearer scene”, “grainy middle”, etc.
And in the depths of the soul there is no peace, there is no that pleasure when listening, only self-deception driven into the head with meaningless terms. This was no longer the girl I knew.
A week of listening was enough to understand that you need to return your native ULF-P on three microcircuits. But here's the problem, I already started burning bridges when I soldered one K157UD2 (DA 1.* in the diagram) from the dismantled preamplifier, which went to repair the indicator. I was puzzled by the search for information, I understood in more detail the device and operation of 101. I came to the conclusion that the exclusion from the DA 1. * scheme does not lead to negative consequences. (DA 1.* in the preamp is used to match the piezoelectric pickup, for me it's not relevant).
The signal from the source after the input selector is fed to R9 and R10, respectively. Interstage tanks C23, C24 are out of harm's way replaced by new non-polar ones. First launch after modernization: many experiences and one small hope to return the former voice...
From the first notes of familiar compositions, I realized that the goal was achieved, basses live in 101 again! I don’t know how to describe the sound in a sweeping way, I’ll just say: you either like it or not. Now I like it! So, at the input of related events, the third version of the RT 101 preamplifier appeared - two microcircuit.
Cotton in the speakers when turned on was the result of a malfunctioning protection. Extraneous sounds when the amplifier is turned off, just like the reaction to the on / off household appliances in the apartment, are eliminated by installing a noise-suppressing capacitor with a capacity of 1 μF and a voltage of> 280V to the contacts of the mains switch.
The volume, balance and timbre controls are cleaned of dust with an air stream and lubricated (Ciatim 201 grease).
In addition to the pre-amplifier, the following changes were made to the design of the RT 101:
The native input switcher, together with the corrector amplifier, has been removed.
Instead of the native one, the input selector for three sources is made on a biscuit, which previously served as a Copier switch in the amplifier (SA2 on). The switch has 4 pairs of contacts, so it allows you to break even the ground of incoming signals.
Connectors for connecting sources are standard RCA, two pairs on the rear wall and one for “hot” switching of sources on the front panel (in places where the “five” connections for tape recorders previously rested). The openings on the front panel after dismantling unused switches and connectors are closed with aluminum-looking plugs (Dubond material).
AT result the amplifier has lost its value for museums, but it is compatible with modern sources and working.
This completes the first part of the work. The second one is more complicated, as it was decided to ennoble the hull, to give the final “gloss”. I plan to veneer the top cover, make a new bottom, correctly arrange the back panel with connectors. What I will definitely tell dear readers in the second part of the article.
Refinement of the amplifier "Radio engineering U-101"
So, let's begin!
1.
Source of power.
Power supply circuits may vary slightly!
To get a decent output power, you need to have a decent power supply. Let's use the gift of the transformer manufacturers: the entire secondary winding is made with one thick wire (0.8 mm in my opinion). Therefore, it is quite possible to switch the power supply of a powerful rectifier VD5…VD 8 from pins 4 - 4* to 3 - 3*, which will increase the voltage from +/-26V to +/-31V. At the same time, a low-current rectifier VD 1… VD 4 becomes unnecessary and is removed along with the wires, and its storage capacitors C2 and C7 are connected in parallel with the corresponding capacitors of a powerful rectifier. But all connections with contacts 5,6 and 9,10 should be preserved.
Then the witchcraft begins.
1. We determine the geometric mean between the ground terminals of the capacitors C2, C3, C4 and C7, C8, C9 on the board of the filter capacitors, clean and tin it. We assign this point as the main common point of the entire amplifier.
2. From it we start up 2 thick wires to the minuses of the output connectors.
3. From it we start up common wires to the UM and UE.
4. From it we start up 2 wires to contacts 6 and 6 * of the transformer, removing the jumper between them. At the same time, we remove the connection between the rectifier board and the case.
5. We organize the connection of the common wire with the case at the input connectors of the amplifier.
6. And check that there are no more contacts of the common wire with the case anywhere else.
And finally, we connect a 0.047x630V capacitor in parallel with the primary winding of the transformer to suppress impulse noise from the mains. 
After removing VT 6 and VT 7, installing a jumper, replacing R 10 with a diode D 7 and shorting R 15, the D 7-VT 5-R 11 circuit turns into a diode stabilizer for the current source on VT 8, which is already powered by the swinging transistor VT 10 To reduce non-linear distortion, the swinging transistor VT 10 must be high-voltage, powerful and with a high gain. just meets these requirements, so we replace the original transistor with a more suitable one. The classical scheme. Only the R 42 resistor breaks the idyll. It is soldered from the print side into the notch of the printed conductor near the VT 2 collector. The introduction of this resistor increases the stability of the entire PA and allows you to get rid of compensating capacitors C4, C5, C9, C10, as well as resistors R 20 ,R 21. Side effects of the introduction of R 42 will appear when listening.
For normal operation of an electrolytic capacitor, it needs a charging potential of 0.6V, but it is not on the C3 plate. Therefore, there should be a non-polar capacitor here, limiting the bandwidth around 5 Hz. Hence the nominal value of 22 microns NP.
The setup is normal: connect an ammeter to the power break and set the idle current to about 40 mA. Then restore contact and start working.
color removed components are highlighted.Numbering corresponds to standard schemes e.
3. Preamplifier .Djvu 60 kb
Chip DA 1 is included in the preamp solely to match the piezoceramic pickup. I think that now this is no longer relevant, but it adds noise, and therefore we boldly throw out the DA 1 chip along with all the strapping and throw a jumper using the freed holes on the printed circuit board.
Newly introduced or changed components and jumpers are highlighted in red, and blue color removed components are highlighted. The numbering corresponds to the regular scheme.
This figure shows the DA1 chip and the components that should be removed along with it on the U5 ULF-P board.
Next, we more accurately adjust the loudness circuits to the volume control. Then we expand the bandwidth of the DA 2.1 and DA 3.1 amplifiers both in HF and LF and adjust the parameters of the tone block. To return the supply voltage of the DA 2 and DA 3 microcircuits to an acceptable direction, it is necessary to correct R 47 and R 48.
The preamplifier includes trimming resistors R 24 and R 26 to adjust the gain of the entire amplifier. Setting conditions: at the input - 0.5V 1kHz; volume control - to the maximum; at the output - 14V without load, set with resistors R 24 and R 26.
rednewly introduced or changed components and jumpers are highlighted in color, and blue color removed components are highlighted. The numbering corresponds to the regular scheme.
This diagram shows the ULF-P refinement circuit, the DA1 chip is not shown.
5. Corrector UPZ-15.
To date, all known moving magnet magnetic pickups operate with a correction capacitance of 470pF. Accordingly, the capacitance of capacitors C1 and C2 is changed to 470pF. 6.Payment of inputs.
To expand the bandwidth down from 20 to 7 Hz, you can increase the capacitance of capacitors C4, C5, C14, C15 to 0.33 microns. This is at the end of the work as the cheeks puff up.
This treatise was compiled on 3.06.09.
/ nivaga /
or by mail, address attached.
At the dawn of my receiver activity, Speedola 232 was considered the best amplifier, Ishim was one step lower. Then came "VEF 216" - small, wildly stylish, with a built-in power supply and excellent sound, it brightened up gray everyday life and sometimes the same gray weekend. Then "Wilma" appeared, a little later - columns to her. Life has become more fun: firstly, stereo, and secondly, sound, as we say, can be “heaped”, although I don’t like loud music.
And all of a sudden, just recently, I realized that she had a very small margin of volume control, so let's say “quiet -> normal -> loud -> I-start-to-compensate-Freud-like -> no longer spinning” (2 x 4 W) . I wanted something more powerful.
But how are we usually? We say "normal available amplifier" - we mean "Radio engineering U-101" (2 x 20 W), we say "Radio engineering U-101" - we mean "normal affordable amplifier". Maybe the "duckling syndrome" also played an important role - I came across one of these for repairs, what's inside, I know about it.
In general, I found and bought.
Yes, the shed is still the same, it takes up a lot of space on the table, mainly because of the depth.
Only the interconnect cable DIN5 - DIN5 was included in the kit, so for the initial check I also had to get Wilma. We played. The sound is normal, nothing out of the ordinary. I was even a little upset that I did not know how to hear "airiness", "warmth" and "transparency". Still, the first class, it seems to be like it's time.
I will conduct a tour for those who are not at all in the subject of what is under the hood of the 101st. The closest thing to us is the pre-amplifier-tone block and the board of the vacuum luminescent indicator. The second row is a capacitor bank (6 x 2000u, 63 V), two diode bridges (small for small household needs (+/- 31 volts) and powerful (+/- 26 volts) for powering final amplifiers) and a transformer. The third row is the input-switch board, the protection board (you can see the relay over there) and the final amplifiers. "Electrolytes" are full, so
Only who knew that I was guessing and this my favorite phrase would still come out sideways.
Okay, now more about blocks.
preamplifier. The suspect dog almost fell off his chair when he saw this. I read on the Internet - it turns out that there is such an alteration when the first K157UD2 in the timbre block is removed. If you do not listen to records, then it is quite possible to do without it, there will be less distortion. Looks like the previous owner thought so.
The shielded phono preamp box should be on the switchboard directly below the colored wiring harness from the PSU. The previous owner definitely decided that the time for vinyl had passed (as well as the time for four-legged devices - “Radio Engineering” turned out to be lame-footed, without a back right one). However, one of the simplest and most effective alterations of the "101st" is just to remove the phono stage, it sometimes starts to make wild noise and even receive the radio. So who knows, maybe it's for the best - I still don't have a "turntable" and it's not expected.
A little to the right is the protection board. "Electrolytes" were replaced with 85-degree ones. At first glance, everything is fine here. But this is only a first glance.
I was wildly outraged that all the boards were made of getinax (“Wilma” is a second-grader wholly on textolite).
Final amplifiers, or, as they are also called, "ends". A little dusty. Also with traces of replacement containers.
indicator board. There are two extra resistors on the side of the foil - I didn’t take pictures.
In general, what can I say: life dragged a Latvian. Nothing, the white horse is already on its way, right now we will save you, princess.
I was surprised how discrete the volume control was made: with a ratchet. Those who are accustomed to "analogue" regulators can remove the spring or press and fix the "dog".
Tests after replacing almost all containers showed: clapping speakers. Both when turned on and when turned off. And first class too! Strange, where does the defense look? Although what is it? It's nothing! Then something interesting began.
Turned on the amplifier, listened for about ten minutes. Suddenly 50 Hz appear in the right channel, louder and louder, they do not react to the sound reduction. The indicator dances with the right channel, the amplitude of the waves is increasing. By ear, it is perceived as a motorcycle idling. I turn it off, scratch my turnips, go to regulate the quiescent currents of the “ends”.
I set it to 45 mA. In the left channel, don’t understand what happened at all, the multimeter went off scale at 200 mA.
I turn it on again. It works for about ten minutes, the right one starts to growl again. I pull off the input plug from the right “terminal” - the rumble and the “motorcycle” go to the left. I pull off the input from the left - almost immediately the indicator goes off scale, so much so that the S-30 shines with an overload (even though I saw these LEDs in action). The multimeter shows that the “constant” rises at the output (up to 13 volts), then the relay clicks like a bad one. Began to understand.
Well, the coolest alteration in this "Radio Engineering" - Attention!- the output wires of both ULFs are soldered to the output wires of the protection board. AT detour protection, Carl! The relay can click as much as you like, but if a "permanent" comes, then without thinking twice, it will go directly to the acoustics. No wonder the overload indicators were on. After the restoration of the status quo, the protection began to correctly process the "motorcycle", that is, not to let it go to the speakers when the indicators were already dancing almost under the "ceiling". "Motorcycle" also changed - I found myself a warm, I would even say, hot garage in the left ULF, and settled there, almost immediately after turning it on, starting a fifty-hertz song.
I decided at my leisure to still pick up the "terminator". Here, as with periodontitis, you can pull out a sick tooth, or you can treat it. Our dentist friend says that always, as long as there is an opportunity, it is better to treat. Something native is closer to the body.
It took some time to look into the ULF-50-8 saloon, but as soon as he arrived, he immediately broke their chairs and tables, broke the dishes, challenged all three-legged cowboys in turn to a duel with a transistor tester. I didn’t like KT837N with h21 more than three hundred (50-150 according to the reference book and 60 from another of the same). I replaced it with KT818G, but it burned out from the power supply, even a fragment of some track annihilated.
Yes zadolbala this "Radio engineering"! Such a hard break!
And just then friend Andrey, a big troublemaker in the field of electronics, comes, looks at all this (and the sluggish repair has been sluggish for a couple of weeks) and says that he would buy ready-made boards for the TDA2030A and install instead of these problematic "ends". What's the difference - 20 watts or 18, and the hassle is many times less.
And I realized that he was right. All the same, the authenticity of "Radio Engineering" is already a big question, there is nothing to lose. Of course, the move is risky. Fans of "honest Soviet transistors" will scoff at me for replacing "cool Holton" with "soulless microcircuits." Chip fans - for not being a TDA2050 or TDA7294. Fans of tube sound will snort anyway.
Well, what am I? I am no longer restoring the amplifier, I am building a Chevy.
Ready-made scarves were found on the Internet, the question arose with food. TDA2030A can operate at voltages up to +/- 22 volts, and Chevy's native amplifiers consumed +/- 26 volts. Normal people would probably rewind the transformer or find another one. But this is long and expensive, the game is not worth the candle, especially since I specifically quarreled with this game for her boorish behavior. But what if we bring the U-101 closer to the zero class? "Odyssey U-010", for example, has stabilizers for ULF. Only there is a mountain of transistors, and I will take L7820 and L7920, and there will be +/- 20 volts. True, I did not find any mention on the Internet that someone did this, and is it legal at all, but oh well, I’ll be the first, I’ll figure it out myself, I’ll try.
I gave the left ULF board to the stabilizers and shifted it to the place of the right channel, and fixed the TDA-shki where the left one was.
LEDs indicate the presence of power. I always try to make an indication of switching on - I have come across more than once when another home-made product does not work, even if you crack, but the problem turns out not to be in transistors or even in a bobbin, but in an unconnected “plus”.
And so, I start these seven and a half liters of electrolyte ... The protection thinks for a couple of seconds, click! .. Oh, "motorcycle", hello. So you, dog, it turns out, you live not only in the ULF. It is necessary to pick the tone block.
First of all, I replaced the wires from it to the TDA-shki with shielded ones (the screen is hung on the "ground" only from the side of the tone block). Not that. I replaced the two remaining non-polar capacitors (if there are no non-polar ones, then you can connect two pieces “plus” to “plus” twice the capacity), one was nothing, one was dry. Also not that. I looked that there is such a special living in the preliminary. Two K157UD2, normal trouble-free microcircuits, how much rubbish has already been collected on them. Are they really trouble free? No one else to blame. I uprooted one of the left channel (1983, brown body) and replaced it with a fresher copy (for this I had to remove the aluminum muzzle and the entire tone block). I turn it on - but it does not buzz! But it’s too early to rejoice: the sound is vile, “sand” appears at high volume. I spit on integrated technologies, idolize Wilma's multi-transistor circuitry, and finally, I look at the paper that was attached to the TDA-shki. " If self-excitation of the amplifier is noticed, solder a 2k and 82p circuit between pins 2 and 4”(This is also in the datasheet). Well, I soldered ...
***Digression***
A hare is walking through the forest, he sees: a fox is stuck between the trees. He went, did all sorts of bad things and moves on. Meets the wolf:
- Hare, are you happy with this?
“So the fox got stuck there, well, I… I threw a couple of sticks!”
The wolf also ran there - did the same. Satisfied, a bear comes back to meet him:
- Wolf, why is your face already shining?
- Yes, the fox got stuck there, so I threw a couple of sticks ...
The bear thinks, “Let me go. Descended, returns to the wolf, the whole already glows with happiness. Wolf:
- Well, did you throw a couple of sticks?
- Not at all! There were no sticks ... So I threw cones at her!
So I still showered "Radio Engineering" with cones: not a grain of sand was left. She plays loudly, nobly, the LEDs in the acoustics can even wink - “Wilma” only clicks her teeth with envy. But she also found a job - it serves as a pre-amplifier, because the only 3.5 mm cord - DIN5 I have is not wired the way it should be "101st". Alone, she plays quietly from this cord, but cleaner - "Wilma" brings its second-class noise.
Important point: radiator temperature. The stabilizers are cold even under a good load, the TDAs heat up, but you can completely keep your hand on them. The hottest corner of the heatsink is the one closest to the input board. But even there, the temperature is very, very far from anything exciting.
And now, it seems, everything is fine, you can sit, listen to music, watch kintso ... Stop, ep-p-ponsky tape recorder! I worked for an hour and a half or two, and suddenly pink noise appears in the right channel. Well, to hell, it seemed, with him, so he is growing! Then, by nature, it becomes like a tide on the sea. Then some wild modulation begins.
That's crazy stupid. If you let it cool down for ten minutes, the noise goes away, but then comes back again. I soldered some little things, corrected the wires (it turned out that the input of the right ULF went exactly above its output, and this is a prerequisite for creating positive feedback and turning the amplifier into a generator), even replaced the TDA-shku (suddenly they gave a defective one). Sat down to test.
It looks beautiful and convincing (at night the indicator even blinds), but again an hour and a half or two passes, and the "sea" begins. I shorted the output of the right channel from the preliminary to the "ground" - the noise disappeared. And then I thought for the second time - what is there in the timbral block? Another K157UD2- whispered amateur radio luck, no one knows where before staggering.
The Chevy cooled down a bit, when you turned on the noise was gone. I began to drive a screwdriver over the microcircuit ... Gotcha, animal: here you have noise, and hum, and 50 Hz for tea. Change immediately! Oh, and what, ran out, or what? Exactly. I had to disassemble homemade dial indicators, but it was worth it. An hour, two, three, six - and no noise! Finally!
So believe these "rods".
The problem of lameness was solved surprisingly simply: suitable legs were found in the local radio store (foreground).
They are called "legs for quick installation." Indeed, it takes longer to pick a hole in the bottom than to fix the leg.
The pre-amplifier annoys me the most. Either I don’t understand anything in circuitry, or something else, but +/- 31 volts included in the tone block after the resistors R47 and R48(1.5 kΩ) turn into +/- 15 volts (blue dots). Where is Karl? In my Chevy, 1.2 kOhm was soldered from the factory, and +/- 22 volts went after them. I replaced it with 1.5 kOhm, and even one-watt ones. It became +/- 19 volts. Still way off the charts.
Therefore, another solution peeped from the Odyssey is 15-volt zener diodes (1N4744A) for power. Was it really so difficult to do it at the factory, at the design stage?
The input selector, which is so popular on the forums, turned out to be a very useful thing. It is already difficult to imagine the situation when more than one input cable is connected to the U-101 (unless the lucky person has the complete Radio Engineering 101 Stereo complex: tape recorder, tuner, turntable), so you can use it otherwise, as a function mute(temporary mute). By switching to another input, you can attenuate the incoming signal to a barely audible rustle, without even touching the volume control (the switch uses K190KT2P, field-effect transistor microcircuits, which, no matter how close, but slightly pass the signal - this is not a relay).
But they can play such songs with Wilma. So the hand reaches out to turn up the volume.
Maybe a little later I will replace the TDA2030A with the TDA2050. It's impossible to go "fast enough".
P.S. I listened to the Chevy for a day and a half, then carried out minor repairs to the Wilma and put it on an electric run. And the sound, and the sound! The 157s hiss (there are four of them per channel in the ULF, plus one in the recording-playback amplifier), there is no volume level “yes-I-have-serious-problems-according to Freud”, the basses are too hammering, then they are sharply lacking … It turns out that you get used to good things very quickly.
P.P.S. I smiled for a very long time when I saw this correlation on the ad site:
First of all, we will deal with the most important element of any system - its heart. The amplifier has, you guessed it, a power supply. We will finalize it following the advice of Nikolai Vasilievich + add a few features from ourselves.
All wires inside are assembled with special ties. For the first time I see such accuracy in Soviet technology. Although, most likely, I simply did not come across such samples.
Loosen clamping screws
disconnect the cable with power from the preamplifier
display unit, while unfastening the tie
and final amplifiers, while also removing a couple of couplers.
That's it, the easy way is over, now you have to pick up a soldering iron. Unsolder the power supply from the input board. Yes, kids, never solder on the couch.
By the way, I still have not figured out where to find the corrective amplifier for the player here. It seems like a separate block is located on the input board, but at the same time, some additional microcircuit is on the preamplifier. Okay, we'll figure it out along the way. We solder the zeros going to the output to the speakers and to the case. Soldering is hard, my 25 watt soldering iron can handle it with difficulty.
Okay, of course, you can still solder off from the transformer and the protection unit, but something is too lazy for me, especially since the power supply has already received more than sufficient mobility for further manipulations with it. The girl moves to the table.
Well, let's start by soldering the capacitor into the network circuit in order to protect our baby from all sorts of unnecessary interference. This one from an old monitor is fine.
We proceed with the finalization of the PSU itself. As Nikolai Vasilyevich wrote in his newer article, it is not at all necessary to transfer all power to 31 volts, it is enough to power the terminals to the maximum to get the maximum return, and put all other consumers on a 26-volt "diet". Among other things, this will help avoid many problems, in particular with overheating of resistors in the display unit.
I will not breed zero as Nikolai Vasilyevich advises. Something seems to me that there will be much less tangible benefits than hemorrhoids with new wires. Moreover, the iron case should already protect against interference, according to what we were told in physics.
Let's start by swapping the 26 and 31 volt leads from the transformer to apply more voltage to a more stabilized section. (Although, given that 10,000 microfarad capacitors will be used, this benefit becomes slightly doubtful, because everything will be in chocolate anyway, but nevertheless)
Swap the wires on both 4th and 5th terminals of the transformer. Now, as expected, more voltage flows through the wires of a larger cross section.
We cut out (anti)filtering capacitors MBM. Never loved them.
We proceed to the replacement of the main "barrels". It's a pity, but they will have to be thrown away. It is unlikely that even a third of the declared capacity remained in them.
As it turned out, the process is much simpler if you remove the plastic gasket.
And now we are washing down our 10 milifarad monsters here. Jackcon, of course, is not the most expensive brand, but for our purposes - just right.
What do we end up with. The capacity has increased by 5 times, while the volume has decreased by 2. Progress, epta!
And now - the promised trick. We solder in parallel to each direction along a non-polar capacitor of the k73-17 type. Nikolai Vasilievich does not have this, but according to many close to the topic, this increases the quality of the return at high frequencies. Yes, yes, the power supply in the amplifier is a very important sound-forming element! What did you think? The world is not at all what catches the eye at first sight.
After the third inclusion, it became clear that the diodes of the small rectifier were smoking. When measured, two of them were broken. Who knows, maybe when you first turned on something unsuccessfully shorted, or 10 millifarads for them is too much of a burden, but, in any case, there is no turning back. There are no diodes either, so tomorrow I need to run to the store.
But, we will not be stopped by this minor nuisance! Muahaha! We continue to test a larger rectifier.
At first, the author was very surprised why the larger rectifier outputs 66 volts instead of the expected 31. But then he guessed to look at the circuit and saw that -31 and +31 were written on it, i.e. the total potential difference is 62 volts, which is the same as 66, only under load.
Well, hallelujah, brothers and sisters, the engine is almost ready to carry us into a bright future filled with divine sound. There are a couple of small but necessary details left, and we will move on to the most interesting part of our story. Amen.
Today I will tell you how I restored the Radio Engineering U 101 amplifier, 1985 release.
The device is very maintainable, and in my case there were no breakdowns. Only a small modification was made to replace the connectors with modern ones, and the replacement of all electrolytic capacitors.
So the first is, of course, the power supply:
We change all dried-up cans 50v 2000uF modern 63v 6800uF.
The main thing is to observe the polarity and carefully solder the contacts, trying not to overheat the capacitors.
Result:
True, I went a little too far with chemistry, and as a result I lost all the inscriptions ....
But for me it is not critical, because. I know all the twists. Next in the photo is one of the amplification channels with field-effect transistors:
Later, some of the audio wiring inside the amplifier will be replaced, and the wire bundles are tidied up:
Testing. The speaker system is connected directly to the amplifier wires. True bypassing the protection relay. About 10 years ago I turned it off, and now everything had to be returned to its place:
Checking channels one by one:
We return the front panel to its place, at the same time and install the twists in place. A kind of No Name amplifier turns out:
By the time all the electrolytes in the amplifier were replaced, it was time to work with a file and a hacksaw:
In this, small and very convenient vise helped me a lot:
Detail for attaching input jack sockets:
Installing the input connectors in their places:
This is a tone block. Capacitors in it are both polar and non-polar. Crisp variable resistors VDshka were also processed:
And setting them in place:
I kept the front panel of the amplifier, modernizing only the connectors on the rear panel. The input selector was also removed as unnecessary. the amplifier will only have 1 input source. And from the input, the signal goes directly to the tone block. In general, in my opinion it turned out great:
As a result, the amplifier will have to work with the N-Monitors 100 acoustics for some time. Then it will go to service the Amfiton 35ac-018 acoustic systems that are now being restored. Let's see how he will show himself in the work.
Thank you for your attention!
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