2 in 1 effect problem: transistor short life

[poppyman]

Hello,

I've tried to put 2 effects in one box following the wiring layout at GGG:

http://www.generalguitargadgets.com/pdf/two_in_one_wiring.pdf?phpMyAdmin=78482479fd7e7fc3768044a841b3e85a

I put a red llama OD clone for fx A and a SHO clone for fx B. Both worked very well and A+B worked too.

After a few hours of playing the boost didn't work anymore and instead of boosting the sound, it was reducing it with the knob cranked with an increasing buzz.

I checked and realized the SHO boost transistor (BS170) was dead. I didn't worry much as I read it could happen. I replaced it but after a few hours (not a row this time) of use it was dead again                (while as before, the OD and both led were working ok)

Could someone tell me what is wrong?
is a wiring issue?
is it a defect part? (I tested all the part of the SHO everything is normal though)
could it be a power adapter issue? (the guy I lended to as a "one spot" plug and as tonnes of danelectro effects which make weird stuff when he plugs his fxs).
Or could it be the huge amount of signal when the 2 fx are on at the same time? (the SHO and red llama can be REALLY super loud)

sorry for the dumb questions but I build many effects but my electronic knowledge is close to zero.

Tahnk in advance for your help.

poppy

[runmikeyrun]

Can you post voltages for the transistor of the SHO? 

[Jaicen_solo]

The SHO is sensitive to voltage spikes, that's why Zach used to ship spare transistors out with each one, not sure if he still does.
Anyway, maybe you could ground the circuit input when in bypass, that should bleed any voltage to ground and stop any popping as well.
I ground the input of all my circuits in bypass, I think it's good practice.

[poppyman]

thanks for your answers guys.

Unfortunately, runmikeyrun, I'll can only use the tester the weekend (I don't have all my gear with me).

Jaicen_solo, I'm sorry but my ignorance of electronic kicks in here: I don't think I know what you mean by "grounding the circuit while in bypass". Should I connect a specific lug of the footswitch of the SHO to ground? Or wire some other thing to ground?

I was thinking of swaping the SHO with a more classic boost instead (stratoblaster, micro amp or LPB). would it be less "sensitive" or it would end up like the SHO and have its transistor killed?

anyways, thanks guys.

[runmikeyrun]

If it is the voltage spikes causing it a 1M pulldown resistor at the input might help too.  Let us know when you get those voltages.

[poppyman]

ok, I couldn't wait til the weekend so I borrowed a DDM. I never tested transistors before, just resistors to check I put the proper value so it was a "first time" for me.
It seemed to work fine except the values were still going up or down very slowly after a long time.

Here are the values (I did a test with a new BS170 in and then a new BS170P (supposed to be better) in)

BS170 --> S: 1,43               G: 2,52              D: 6,7

BS170 P --> S: 1,75            G: 2,43              D: 6,43

voilà. It doesn't mean much to me but if you guys can figure out if it's normal or not, it would be very nice.

I didn't know what was a pull-down resistor before but I think I understand what it does should I wire it like this?

(oups, couldn't insert my photo here, sorry) --> add the 1M resistor between the lug 1 of the foot switch to the "in" of the SHO PCB?

Does it affect the sound/output of the effect when it's in use?

Thanks again for your help.

[poppyman]

or does  the 1M pull-down resistor go from the input of the PCB to ground? (sorry for my lack ofr knowledge)