small mystery soviet circuit with transistors

[ELS122]

I just found this soviet circuit laying around and I have no idea what it does...
*edit: updated the schematic. also the + and - were labeled on 2 wires, not sure if it's right

[ataradov]

The component is a KT315 (NPN) or KT361 (PNP) transistor - https://en.wikipedia.org/wiki/KT315

The one shown here is KT315. KT361 would have "-" across the letter ("-A-").

[ogden]

D818A is 9V zener. That board does not seem like complete circuit.

[wraper]

The one shown here is KT315.

Letter on the left upper corner is suffix for KT315 series. KT315A in this case.

KT361 would have "-" across the letter ("-A-").

Not necesarily. KT361 often has simply letter in the middle. Package for both may be orange or yellow. Sometimes with brown tint. In extremely rare cases black or green.
There are also a few other parts in such package though, like КП313. But much less common. Black variant of this package is normally used for varicaps.

[ELS122]

I just found out. those "bulbs" are not bulbs at all. there cat whisker diodes!

[ELS122]

so I found one really similar transistor in the same packadge and also orange but it has a russian G on it. is this like a KP315G?

[ataradov]

Yes. Your chances of finding anything other than KT315 or KT361 in this package are slim to none.

[ELS122]

oh, yes sorry for bumping this post. I also found out myself. it's just a KP315, not a KP315A or etc.
thank's anyway for the response
edit: wait no I was wrong . I found a list and the specs here if anyone want's them http://www.datasheetcafe.com/kt315-datasheet-npn-transistor/

[ELS122]

ok so I got curious again about this circuit, was looking at my previous schematic and it was totally wrong, I redrew a schematic attached to this post:


I think it's like for a galvenometer, like perhaps a complicated AC messurement board, because 1. it's round, 2. has screw terminal outputs, 3. it rectifies the output.
at least that's what I think...

I'm gonna try powering it with 12 volts, and see what it does.

I have a suspicion that I found it just laying around because it didn't work, because the emitter of the transistors is directly connected to ground which from what I heard you need some emitter resistor or it's very unstable...

the diodes used were cat-whisker diodes, I'm not quite sure I got the polarity right, I assumed the semiconductor part was the cathode (stripe) and spring was the anode...

[AlexITC]

In the photo KT315A, I recommend that you use KT315I instead, due to the higher operating voltage, there is a margin for overload. I have repeatedly encountered the failure of these transistors. On measuring equipment of the Soviet era.

[Bud]

The small electrolythics are likely dead.

[ELS122]

The small electrolythics are likely dead.

oh btw I should've posted this in a different category, it isn't really about repairing it, more about questioning what it is for...
I recreated the circuit in LTSpice and it outputs a really negative AC on the output, around -9V peak when there's AC on the input...
so that explains why the positive labeled wire is connected to ground...

[mykrowyre]

To me it looks like a 2 stage amplifier but the last set of diodes has me puzzled. You sure they are diodes?

[mykrowyre]

I'm suspecting an amplifer for a mocrophone in a handset.

[Kleinstein]

ok so I got curious again about this circuit, was looking at my previous schematic and it was totally wrong, I redrew a schematic attached to this post:
(Attachment Link)

I think it's like for a galvenometer, like perhaps a complicated AC messurement board, because 1. it's round, 2. has screw terminal outputs, 3. it rectifies the output.
at least that's what I think...

I'm gonna try powering it with 12 volts, and see what it does.

I have a suspicion that I found it just laying around because it didn't work, because the emitter of the transistors is directly connected to ground which from what I heard you need some emitter resistor or it's very unstable...

The ouput looks like a rectifier and thus an AC measurement circuit looks sensible.
The 2nd stage with the transistor direct to ground is indeed a problem.  Maybe the 13 K resistor for the base is not going to VCC, but the collector ? That would make the stage more stable. An unstable operation point would effect the AC gain and would thus be not suitable for any useful measurement. So it may be more like an on/off indication for the presence of a AC signal.

[Vtile]

A fuzzbox? 

First transistor creates transimpedance amplifier, but I'm not sure about the 2nd stage.

[ELS122]

A fuzzbox? 

First transistor creates transimpedance amplifier, but I'm not sure about the 2nd stage.

tried it, doesnt make a good fuzzbox 

it seems to be a frequency messuring circuit, because it's not affected by voltage a lot, in fact varying the signal from 0db to around -37db at 200hz doesnt change the reading at all, then bellow -37db it drops off like a rock.
but frequency changes it a lot. at 0db I get full deflection on a galvenometer attached to the output at 240hz (I dont know what the current it for the galvenometer, and it's been dropped so it's probably not accurate, just using it for a reference)
and 50% deflection at around 70hz

so I'm suspecting it could be for a line frequency meter or something of that sort, maybe I'm just not driving enough voltage into the input at lower frequencies, or the meter isnt correct for it.
anyway, it seems to be a frequency meter circuit

I also double checked and yes the 13k resistor to base is indeed connected to VCC, and it is very clear that it is.

[ELS122]

now thinking... maybe it's a tachometer, like an external tachometer, because 200hz would be 6000rpm for an inline 4 engine... it would certainly make a good tachometer circuit, but I dont think it's meant to be inside the car, it just looks off for that, but maybe an external tool you clip on for tuning...