Some sort of Russian amplifier, what is it?!

[ibvee]

Just picked 3 of these up yesterday at a local dumpstore. Found 1 with a german translation beneath the big rotary switch which said "Amplification" (Verstarkung). The switch at the top was labelled "1-pol" and on the other side "2-pol". I managed to translate the russian text beneath the 3 state switch (with google translate) to "correction filter". All in all, I still don't have a clue as to what it is. Probably have to draw out the schematic by following the leads. However the inscriptions on the components are in russian to, so I'm not looking forward to it. 

The tubes used are 2п1п, did a short google search, but no real info popped up. They are marked OTK7 which supposedly means they are military grade.

They just looked to cool to leave them there, and on the first glance I thought they might actually be mic amps, because of the components used. And otherwise I might be able to mod one to a mic amp. However I'd really like to know what these things are, and where they were used.

Sorry for the crappy pictures, had no better camera than my phone lying around.

 

[ibvee]

side picture

 

[ibvee]

And the rear

 

[ibvee]

So far I haven't found any more info, but I finally got around to drawing up a schematic.

Still don't really know what it is or how it's used. From my limited experience with tubes, I can see some parts are missing, which makes sense, as it is only a single module. But I'm still really curious what it's supposed to be.  Does anybody have a clue? Also, what parts could be missing. And what I really don't get is, where doe the tubes get their Anode voltage, which according to the datasheet, should be 90V?

The transformer at the end measures around 2,1kOhm on the tube side, and 164Ohm on the output. Does this make it a 1:13 ?

Hope somebody can help!

Regards Mic

 

[gemini86]

So there's no power coming into this unit? No connector anywhere?

 

[pucho812]

correction filter is the clue. the unit needs power to run obviously no power lines were drawn for heaters and b+. Back in the day eq's/filters were often called  corrective devices. My first guess would be for broadcast

 

[gemini86]

Are you sure on your tube pinouts?

 

[ibvee]

Tx for the replies already.

I bought the units without any power supply. They're modules from a bigger unit, but obviously an amplifier, as it says 'Amplification' under the rotary switch.

I'm pretty sure on the tube pinouts, I have the tube pinout of the 2P1P (you should read those from the bottom view of the tube, right?).
After studying the schematics some things became a bit clearer for me though. Filament voltage is applied by connector 231 pin 2, plate voltage (B+) is applied by connector 232 pin 1 (the bottom one), that way it reaches tube U2 via the transformer, and tube U1 via R8, and grid 2 of both tubes also get their voltage, as is recommended in the datasheet of the tube.

Still I'm not sure whether signal is applied via the 231 pin 3 (the top one) or one of the pins of connector 230. I haven't seen a unit with an inductor in the signal input before, but I haven't seen that much units of this type before, so me not seeing it doesn't mean anything. Does anybody recognize this sort of input stage?
Also, what function could the circuitry around the mA meter have? The S2 is labeled on the unit with (in russian) "pole 1" and "pole 2"...

 

[Matador]

In Mother Russia, microphone amplifies you! (sorry couldn't resist...)

Most pinouts are read from the bottom in a clockwise direction.

 

[PRR]

Schematic re-drawn, more conventional though sloppy.

Gain of two pentodes should be over 500. OT DC resistances are not a great guide to signal voltage ratio, but 10:1 may be a working assumption. Gain near 50 from input to output.

Input network 1u against 1.1Meg is 0.15Hz

Coupling network 0.5u against 806K is 0.4Hz

150nFd against 60K is 17Hz; 270nFd against 60K is 10Hz.
(But 150pFd against 60K is 17KHz; 270pFd against 60K is 10KHz.)

If "n" is n then response is 1Hz to 17Hz.

If "n" is p then 1Hz to 17KHz.

If 1hz-17Hz, this is sub-audio. Perhaps earthquake detector. (Or underground atom-bomb quake detection.) If 1Hz-17KHz then it is an audio amp.

The 1Meg around V2 is NFB, and some assumption about V1 suggests gain near 500. 1Meg against 1nfd is 160Hz, response will rise at lower frequency, but not much because there is little/no excess gain. 1uFd against 1Meg will flatten response down to 0.17Hz, which seems more likely.

I am reminded of a G-R test-bench amplifier. Batteries for low hum, flat response from the bottom of the audio band up to "high audio" (in AM radio terms, a few KHz).

And then there is that current meter. It was desired to know current to/from the input transducer. Carbon mikes take current, but don't generally need tube preamps with this much gain. Strain-gauges take current but make such small voltage that this is silly. A radio-set detector and AVC make audio and DC, but the DC is not usually measured with a mA meter.

It's a mystery.

However the obvious hacks give you a "color amp" with high gain and probably easy overload.

 

[ibvee]

Dear PRR,

Thank you very much for your time and notes on this! It really helps me understand more, I really like to learn about this stuff. Still plan on reading the Radiotron Designers handbook, but it'll have to wait till I have finished the Horowitz and Hill.

I will redraw the schematic in your 'conventional' way.

I'm pretty sure the 2 filter capacitors are in nFd. However, there's also a state without any capacitors in the circuit. What would that do to the response?

To be honest, I'm not sure whether the 1nFd in the feedback chain of V2 is actually 1nFd, it might have been lower, as my multimeter couldn't really measure it accurately.

What is a 'G-R  test bench amplifier'?

What is the function of the inductor in the input stage? I'm used to amplifiers with a transformer on the input, but haven't seen this before.
What could be the function of the push button in the circuitry around the mA meter, which temporarily disconnects the resistor?

Would a power supply with +90V for B+, and 2,4V for the filament (in this schematic it's connected in series right? as the datasheet of the tube mentions), be sufficient to power this unit? 

 

[PRR]

> a power supply with +90V for B+, and 2,4V

If you do not have to meet original specs, the B+ can be +24V to +100V. I would suggest three or four 9V batteries. They will run a long time, and no hum.

The heaters of the two tubes are shown (in your drawing) in parallel.

Each tube has two heater-segments. The segments may be wired series for 2.4V, or parallel for 1.2V. There is no way to predict which way it was wired. Parallel 1.2V is very possible.

http://www.magictubes.ru/sprav/pdf/2p1p.pdf

How are pins 1 and 7 wired? Jumpered to each other, or not? If jumpered, then they are wired for 1.2V heat.

In US beach-radios, we normally powered such heaters with "1.5V" flash-light cells. The heater load is large enough that the battery quickly sags to 1.4V, then drains to 1V.

The heater polarity IS important. In this chassis, the un-grounded side of the heater must go to the positive side of the heater battery. The heater is also the cathode. By making the cathode mostly-positive, the grid is mostly-negative of the cathode, which is the desired bias voltage polarity.

Hmmmm.... this tube is a "power" tube. It can deliver 0.2 Watts to a load, good for beach-radio. To do that it needs 90 Volts. But you can feed it less, with reduced power output.

 

[PRR]

> a power supply with +90V for B+, and 2,4V

If you do not have to meet original specs, the B+ can be +24V to +100V. I would suggest three or four 9V batteries. They will run a long time, and no hum.

The heaters of the two tubes are shown (in your drawing) in parallel.

Each tube has two heater-segments. The segments may be wired series for 2.4V, or parallel for 1.2V. There is no way to predict which way it was wired. Parallel 1.2V is very possible.

http://www.magictubes.ru/sprav/pdf/2p1p.pdf

How are pins 1 and 7 wired? Jumpered to each other, or not? If jumpered, then they are wired for 1.2V heat.

In US beach-radios, we normally powered such heaters with "1.5V" flash-light cells. The heater load is large enough that the battery quickly sags to 1.4V, then drains to 1V.

The heater polarity IS important. In this chassis, the un-grounded side of the heater must go to the positive side of the heater battery. The heater is also the cathode. By making the cathode mostly-positive, the grid is mostly-negative of the cathode, which is the desired bias voltage polarity.

Hmmmm.... this tube is a "power" tube. It can deliver 0.2 Watts to a load, good for beach-radio. To do that it needs 90 Volts. But you can feed it less, with reduced power output.

What was this module for? I really can't imagine. Wire-tap listener. Power line monitor. Vibration sensor. Roughness analyzer.

 

[abbey road d enfer]

I haven't seen a unit with an inductor in the signal input before,

As mentioned before, it's for biasing a transducer. The characteristics of the circuit seem to indicate that it's not a traditional audio transducer, but still something that can be heard... the plot thickens.

Also, what function could the circuitry around the mA meter have? The S2 is labeled on the unit with (in russian) "pole 1" and "pole 2"...

As drawn, looks just like an on/off switch, but may be a polarity reversal if one wire added. The other switch momentarily increases the meter's sensitivity by disconnecting the shunt res.

 

[ibvee]

Each tube has two heater-segments. The segments may be wired series for 2.4V, or parallel for 1.2V. There is no way to predict which way it was wired. Parallel 1.2V is very possible.

http://www.magictubes.ru/sprav/pdf/2p1p.pdf

How are pins 1 and 7 wired? Jumpered to each other, or not? If jumpered, then they are wired for 1.2V heat.

In US beach-radios, we normally powered such heaters with "1.5V" flash-light cells. The heater load is large enough that the battery quickly sags to 1.4V, then drains to 1V.

pin 1 is not connected, thus my assumption that it would be wired in series for 2,4V. Is there any way to check? Like feeding it 1,2V and checking if it glows properly?

Quote from: ibvee on November 23, 2011, 05:08:22 am
I haven't seen a unit with an inductor in the signal input before,

As mentioned before, it's for biasing a transducer.

Thank you! By biasing the transducer, do you mean that a voltage would have been applied on the 230 connector (via the VU meter) which would have been blocked by C1 (the 1uF on the input), and stabilized by the inductor?

Hmmmm.... this tube is a "power" tube. It can deliver 0.2 Watts to a load, good for beach-radio. To do that it needs 90 Volts. But you can feed it less, with reduced power output.

So by varying the B+ voltage I might be able to get the output of the amp in a workable range to make it a microphone amplifier?
Would I have to remove the inductor on the input, and perhaps the 1uF, and replace those with an input transformer?

can't stop thanking you for helping me! It really helps.

 

[abbey road d enfer]

pin 1 is not connected, thus my assumption that it would be wired in series for 2,4V. Is there any way to check? Like feeding it 1,2V and checking if it glows properly?

I would say a thorough check of the wiring and current measure would be more appropriate. Evaluation of heating by looking at the filament, huumm...

I haven't seen a unit with an inductor in the signal input before,

As PRR mentioned, quite common on carbon mics and strain gauges.

By biasing the transducer, do you mean that a voltage would have been applied on the 230 connector (via the VU meter) which would have been blocked by C1 (the 1uF on the input), and stabilized by the inductor?

Correct. Stabilized not really, just providing a low resistance DC path and high enough impedance at relevant frequencies.

Would I have to remove the inductor on the input, and perhaps the 1uF, and replace those with an input transformer?

Correct. You may have to rework the input attenuator with lower values that would provide proper loading to the input xfmr's secondary.