small mystery soviet circuit with transistors - Page 1
Forum section: electronics / repair

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: August 05, 2019, 09:08:20 pm
content: I just found this soviet circuit laying around and I have no idea what it does... [ Attachment Invalid Or Does Not Exist ]*edit: updated the schematic. also the + and - were labeled on 2 wires, not sure if it's right

author: ataradov
author_rank: Super Contributor
timestamp: August 05, 2019, 09:39:38 pm
content: The component is a KT315 (NPN) or KT361 (PNP) transistor -https://en.wikipedia.org/wiki/KT315The one shown here is KT315. KT361 would have "-" across the letter ("-A-").

author: ogden
author_rank: Super Contributor
timestamp: August 05, 2019, 10:13:40 pm
content: D818A is 9V zener. That board does not seem like complete circuit.

author: wraper
author_rank: Unknown
timestamp: August 05, 2019, 10:38:29 pm
content: Quote from: ataradov on August 05, 2019, 09:39:38 pmLetter on the left upper corner is suffix for KT315 series. KT315A in this case.QuoteNot 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.

author: Deactivated-1
author_rank: Frequent Contributor
timestamp: October 20, 2019, 02:10:14 pm
content: I just found out. those "bulbs" are not bulbs at all. there cat whisker diodes!

author: ataradov
author_rank: Super Contributor
timestamp: February 28, 2020, 05:34:36 am
content: Yes. Your chances of finding anything other than KT315 or KT361 in this package are slim to none.

author: AlexITC
author_rank: Newbie
timestamp: December 20, 2021, 01:50:05 pm
content: 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.

author: Bud
author_rank: Super Contributor
timestamp: December 21, 2021, 05:51:04 am
content: The small electrolythics are likely dead.

author: mykrowyre
author_rank: Newbie
timestamp: December 30, 2021, 09:48:27 am
content: To me it looks like a 2 stage amplifier but the last set of diodes has me puzzled. You sure they are diodes?

author: mykrowyre
author_rank: Newbie
timestamp: December 30, 2021, 09:49:42 am
content: I'm suspecting an amplifer for a mocrophone in a handset.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 30, 2021, 10:45:48 am
content: Quote from: ELS122 on December 20, 2021, 01:24:22 pmThe 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.

author: Vtile
author_rank: Super Contributor
timestamp: December 30, 2021, 05:33:02 pm
content: A fuzzbox?First transistor creates transimpedance amplifier, but I'm not sure about the 2nd stage.