Russian transistor mike preamp help - diyAudio
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Old 21st April 2012, 03:18 AM   #1
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Default Russian transistor mike preamp help

Hi

I have these two Russian preamps that I would like to get hooked up and run

I have almost no info, and translating Russian very tough, as all tech lingo

I was told they are for tape recorders

Schemo-a. is the wiring to the back connectors.

I am assumming that the three arrows going up in the upper left, are the balanced out.
The three arrows pointing down, and the mike or line in???

There is lots of very "weird stuff" on the schemo, and in the units.

The big round can at the right, on the PC board, has a transformer inside, I assume the

mike in??? It seems a massive shield can.

I took these pics of the one I had not cleaned up, so some dust on everything, and the

cover of the round can would not come off, but I will get one off next week.

I can send more pics etc. if interested.

I anyone can tell me anything, big thanks!

Would like to know power in and other basic stuff, also what they are

The other page is the cover of a few pages, manual type thingy...

gEorge
GridLeak.blogSpot.com
Attached Images
File Type: jpg RussPre_a.jpg (147.7 KB, 168 views)
File Type: jpg RussPre_b.jpg (90.2 KB, 161 views)
File Type: jpg RussPre_c.jpg (188.9 KB, 163 views)
File Type: jpg RussPre_d.jpg (229.9 KB, 162 views)
File Type: jpg RussPre_e.jpg (163.8 KB, 160 views)
File Type: jpg Schemo_a.jpg (163.5 KB, 102 views)
File Type: jpg Page_one.JPG (138.4 KB, 79 views)

Last edited by ElectricMan; 21st April 2012 at 03:27 AM. Reason: Forgot to add peeks
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Old 21st April 2012, 05:03 AM   #2
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They are playback amplifiers, have EQ for playback. Schematic is for interconnects only. Do you have more schemos in that book?
That K50-6 electrolytics are horrible. As well as thin red square ceramic caps.
That big can is not a mic transformer, it is 0.3 Henry choke for EQ.
Socket Ш1 is input (looks like electronic ballanced), Ш2 is output (transformer balanced), Ш3 is +33V power and control.
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Last edited by Wavebourn; 21st April 2012 at 05:14 AM.
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Old 21st April 2012, 07:27 AM   #3
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Hi

There are two pages of specifications, no other schemo stuff.
Do you speak/read Russian??
Then the line marked - is the - side of the +33 volts?
They really look fantastic inside, super quality.
Were these used for tape playback in radio stations??
These take the signal off the playback head, so they would have about 60DB gain?
Is the big open (Line out?) frame transformer good quality?
Would these sound good if re-capped??
Are there more of these, and did they work with Russian made tape machines?
Are these germanium transistor?
Here are the other two pages from the manual
Thanks a great deal for any help!
Attached Images
File Type: jpg Page_three.JPG (155.0 KB, 51 views)
File Type: jpg Page_two.JPG (117.9 KB, 38 views)
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Old 21st April 2012, 10:10 AM   #4
keldysh is offline keldysh  Russian Federation
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Hi
-*******************************-
One. APPOINTMENT

Playback amplifier 71U-15 is designed to amplify and
correction of audio signals coming from the magnetic
playback head with an inductance of 60 to 90 mH

Two. TECHNICAL DATA

The gain at a frequency of 400 Hz, dB:
maximum, at least 72
minimachnmy, not more than 52
The input voltage at a frequency of 400 Hz, mV:
Rated 1.55
maximum, at least 17
The output voltage in the range of frequencies from 21.5 to 16,000Hz,
Rated 1.55
maximum, at least 5
Load resistance, Ohm, not less than 600
Distortion in the range
frequencies from 31.5 to 16,000 Hz at maximum gain,
maximum level of output voltage and rated
correction,%, not more than 0.5
The frequency response meets the requirements of
RTM 19-25Z-70 for the rate of 456 mm / s.
Noise level, measured relative to the nominal output
voltage gain 66 dB and a nominal correction, dB,
not more than minus 62
The noise level, measured along the curve "A" dB
not more than minus 72
Voltage litany, in 33 +/- 0.75

Three. DESIGN AND OPERATION OF REPRODUCTION UNIT

Block diagram of the playback (Figure 1) includes a charge amplifier,
telya play U1, U2 charge level indicator, the output
Transformer TP1, TP2 matching transformer, which is exceptional-
denotes a galvanic connection between the outcome of an independent unit and
single-ended input level indicator.
The transformer TR1 is connected to the output of the amplifier board
play in the "Advance" when you turn on the relay R1.
Level indicator lets you control the output signal
board amplifier U1 and the output unit in the "Advance".
The button allows you to increase the sensitivity of the B1 level indicator
10 dB, which is necessary when dealing with frequency control
tape, and the transformer Tr2 TP1 and the disabled.
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Old 22nd April 2012, 06:23 AM   #5
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I think it is not ":Advance", it is "Forward playback". And S/N A-weighted -72 dB. Otherwise good translation.

No, the unit is more modern that those that used Germanium transistors. I doubt you want Germanium transistors, it is a myth about their advantages.
Yes, looks like the amp is from category of civil production of military plant that have some appropriate technologies, but some parts are garbage for cost reduction. Military resistors, military relay, military transformer used for DB-meter. But I can tell nothing about quality of output transformer. I never saw such units before. I suspect your amps are from some MEZ or similar studio tape recorder.
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Old 22nd April 2012, 09:52 PM   #6
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Looks like I found where they from: 25D-36, LOMO
Look at the right rack, in the middle of it.

Click the image to open in full size.
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Old 7th June 2012, 06:01 AM   #7
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Hi

Sorry for not replying sooner

An old uncle of my girlfriend died, and we had family activity that I got lost in.

I also have been working on this, my first website, Blank

I am trying to set up a internet radio station, and got lost in the graphics work as trying to get all to a certain point of completion.

The Siberian Surf Report plays are about a Russian guy trying to keep a small station alive, and his friends.

I also did not get emails from DIY telling me you two had replied.

A. Thanks greatly for your responses

B. I was going to bring these up slowly, and test them, then sell them. If either of you know anyone that might be interested, please let me know.

I feel that I should at least run them and see if they have a good sound, all working, before letting them go, but if there is someone much more familar with these preamps, and would like to experiment with them, fine with me.

Wavebourn, where are the tape recorders in the picture??

Are they audio or DATA recorders?

Is there a Russian website for collectors of this era and type equipment?

Also, I have worked on fantastic sounding Germanium transistor preamps, and I believe you are right, as in these preamps, the transistors were special made, and much better performance than the average transistor of the time. Also, these older preamps had amazing sweet sounding transformers, that helped greatly with the sound.

I re-built two Philips preamps, and the first three stage transistors were custom built, then the OC75 type, then big TO-3 case outputs, giant input and output transformers, massive bass response

All the parts look very good to me, or at least the work in cabling, general design inside, but I do not know about the caps, resistors etc. as you say.

keldysh, thank you for all your work translating!

My girlfriend is from a lold Greek family, and she and her father know the cryillic alaphabet, but the way a Russian thinks or speaks is different, so I was looking at a lot of tearing my hair out!

I am Irish, and my brain speaks differently

Thanks to both of you, I will watch DIY each day to make sure I see any responses.
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Old 7th June 2012, 04:26 PM   #8
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Quote:
Originally Posted by ElectricMan View Post
Hi

Wavebourn, where are the tape recorders in the picture??

Are they audio or DATA recorders?

Is there a Russian website for collectors of this era and type equipment?
Τhere is one tape recorder on top of each rack, maybe they re not that recognisable without the reels.

THey re Audio recorders . Lomo made equipment for cinema.

Cyrillic alphabet is alot more complex than Greek, and even if we can read it aloud, russian makes no sense to us Greeks anyway.

So do U have the whole rack? If yes, get yourself some blank tapes!!

Cheers from Greece
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Old 7th June 2012, 05:27 PM   #9
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The whole racks are audio tape recorders for cinema.
Your units are reproduction amplifiers from such recorders. They are not microphone amplifiers.
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Old 8th December 2012, 05:51 PM   #10
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Quote:
Originally Posted by ElectricMan View Post
I have these two Russian preamps
may I ask you if you bought them on ebay from a guy whos nickname is Polivoks-shop?
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