Thanks all for your informative replies - some went a little into the esoteric for a newbie, but interesting and appreciated nonetheless.

So, what is the way forward with this? Do I just find the relative transistor and replace? Anything to watch out for?

I believe that the attached is now the correct schematic.

Absolutely Enzo - n=1 does not equal a data set. However, I thought it useful to ask the question so I could see if that is a potential problem and  and if there is find a way to prevent this happening again if it is.

With regard to the exact model I emailed Peavey to point out that it was a different model to mine and they have requested I send details of the front and the back plate so that they can determine which schematic is relevant. I will post when they have replied.

Forgot to attach the power amp schematic! Here we go. Will look up the lightbulb limited.

I ended up contacting Peavey in UK for a schematic - Corby is the head office here. The schematic is for the EFX model - mine is the non EFX. I have attached the power amp schematic that they provided - I am assuming that it is similar. The other versions that were available online were the non-transtube which I believe is a different circuit - particularly in the power amp.

Thanks so much for your detailed info on the fuzz face - I am not averse to putting in caps to tame that hf. The authenticity doesn't worry me - I like the sound, the way I get it is irrelevant!

Once again thanks for your help - it is nice encountering such a helpful, friendly forum.

Thanks for that. DC across speaker wires - looks like one of the output transistors have gone I guess.

Why would the fuzzface go into that kind of oscillation and why would it cause the power transistors to overheat?

I am new here and wondered if anybody could help with the following problem?

I have a Peavey 112 studio pro which sounded great - especially clean channel with lots of reverb but then...

I built a silicon fuzzface (BC108) and was testing it out yesterday through the amp. I got sound - albiet a little quiet. There a couple of crackle and then suddenly nothing but a loud low hum - sounds like mains hum. This does not vary in volume or frequency with changes in the amp's controls but is constant and loud.

I am assuming I have knackered the power stage - does this assumption seem correct? If I have would the home made pedal being plugged in have contributed to this and if so how?

Thank you for your help in advance.