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two Russian preamps for sale trade
two Russian preamps for sale trade
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Old 2nd August 2012, 05:19 PM   #1
ElectricMan is offline ElectricMan  United States
diyAudio Member
Join Date: Dec 2008
Location: North San Diego, CA
Default two Russian preamps for sale trade

I have these two Russian preamps that I would like to sell or trade

If a sale, about $125 would be fab, can bargain.

If trade, I need 3-1/2" by 19" rack panel plates, and 3" max high by max 17" wide by about 8-10" deep boxes for rack jobs. I can also use old gear in rack case, by taking the insides out and just using the cases.

Here are two responses from DIY members with some info

I am having a hard time hooking them up, variac them up and doing listen tests, as busy, can do if needed.

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 1 is input (looks like electronic ballanced), 2 is output (transformer balanced), 3 is +33V power and control.
The devil is not so terrible as his mathematical model!
Wavebourn: We Create Creativity!

Last edited by Wavebourn; 21st April 2012 at 05:14 AM.

================================================== =======================


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!

================================================== ========================


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


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


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.

================================================== ==========================

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.

Mesage me and let me know
Attached Images
File Type: jpg RussPre_a.jpg (147.7 KB, 162 views)
File Type: jpg RussPre_b.jpg (90.2 KB, 155 views)
File Type: jpg RussPre_c.jpg (188.9 KB, 159 views)
File Type: jpg RussPre_d.jpg (229.9 KB, 155 views)
File Type: jpg RussPre_e.jpg (163.8 KB, 151 views)
File Type: jpg Schemo_a.jpg (163.5 KB, 76 views)
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