PNP Tonebender mk ii now finished :)

roberty

I'm wondering if one of the clever people here can help a hack me get my tonebender clone working.

There is no signal when engaged but signal is passed in bypass mode. The light comes on when engaged

I got the following Ge transistors from eBay (I know) which I'm guessing are PNP:

T1 Russain G308b approx 70-80 hfe

T2 Russian G308b approx 80-90 hfe

T3 Tunsgram AC125 approx 110-120 hfe

I lined the splodges on the Russian transistors up with the tab indicators on the PCB but it wasn't an exact match like it was with the Tunsgram (pictured)

I've wired it up so DC tip+black lead from battery connects to 9v on the daughterboard and the LED is wired in backwards.  Red + barrel goes to ground

Capacitor polarity appears correct

I've measured the resistors and they measure correct for their positions

There is forward voltage on all the transistors so I don't think I've fried them (was very careful when soldering these)

I'm guessing I've messed up with the transistor weirdness.  How would I troubleshoot this?  Maybe the Russian trannies have a different pinout?  I have a multimeter. As stated I am a complete hack.  Thanks!

Adam_MD

Did you test it before boxing it? 

roberty

Adam_MD said:

Did you test it before boxing it? 

No, but the switching is fine, I have tested with multimeter (-9v, ground input and output)

lasermonkey

It might be worth googling the "pinout" of those Russian transistors, as they are often emitter/collector/base rather than our usual emitter/base/collector.

roberty

I'll desolder it from the box and give it a go

roberty

lasermonkey said:

It might be worth googling the "pinout" of those Russian transistors, as they are often emitter/collector/base rather than our usual emitter/base/collector.

I've emailed the eBay seller about this, he is going to dig it out and send it to me later

Adam_MD

Just had a look and the pinout is different on those russian transistors.  

https://external-preview.redd.it/gYYQRnlddgyiOKM88jcegWfGhYUUx7CZvWwUI-9z6Ww.jpg?width=1200&height=628.272251309&auto=webp&s=3964288ab349a27622c35206a46b6fb6dbdd8c36

roberty

@Adam_MD yes just got the same info from the seller :-)

Middle is collector, dot is emitter and the other is base

There can be no doubt now.  Those pesky Russians!  It is wired in a test harness now which will make things easier anyway

Fingers crossed, could get a bit messy now

Adam_MD

Ouch at least you know what's wrong now.  I always use sockets for weird transistors so I can swop them until I decide what I'm going with.  You can always solder them into the socket once your sure what's in them in staying. 

roberty

Believe it or not I've actually managed desolder and resolder the cans with the pins bent around and it works.  I was not expecting that to be honest

Now I am trying figure out how to bias it. I have to use the bottom of the board as contact points cos it's too cramped under the legs

Thanks for you help @lasermonkey @Adam_MD ;;

Adam_MD

Nice good luck biasing it. 

roberty

Adam_MD said:

Nice good luck biasing it. 

Well the bias adjustment ranges didn't get me to the recommended values, and when I went to test it again it's dead :-/ might just cut my losses and start a new board seeing as it's a bit of a mess and it probably won't sound great anyway

Anyone know a good source for PNP transistor sets?

Adam_MD

Smallbear or pedalhacker. 

roberty

Adam_MD said:

Smallbear or pedalhacker. 

Cheers will deffo socket next time so it can be repurposed

roberty

Sorted! Got a trio of matched AC125s off an eBay seller after a few messages. They bias into the suggested ranges and the pedal sounds fab. A keeper for sure. Worth persevering

oaf

Nice work!