Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Rontone on January 01, 2023, 12:10:23 pm
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Hi all, Happy New Year,
I have a Peavey C30, with a reverb fault, I tested the reverb leads and nothing, open load, the tank itself tested fine
Checked inside and the pin cable connector was wired wrong, and the plastic header part was badly melted from previous owner... I rescued what was there, rewired and now the return is working, I can flick the tank and hear the springs splashing, but no send signal,
So next I thought maybe the IC Chip has gone so no send signal, I do the poor mans test and put it in a guitar pedal and it works [although it may not be powered to the same voltage and show a fault?]
Then thought is it the power to the IC? -15vdc to both the send and return sides, but the send side has a -30vdc to pin 4 of the IC
Tracing back through those parts I noticed electrolytic power cap C47 [at the bottom of the scheme off the bias supply] does not register on my meter, C48 next to it does, although they are in circuit and measured with a normal multimeter so it may be not reading them properly, it may be draining as I am testing?
I can just get my probes to most of the associated parts without disassembling and all seems fine with all other resistors and caps in the reverb circuit,
The amp otherwise works fine, has had a service not long ago, valves work and bias, relay switching works, so all other power rails on the LT side of the power supply where the reverb is powered from are operating,
The only thing I can think is to try another IC in there first, and then replace C47 [can get to it without taking the amp out, its just near the edge]
[Also check out the free floating caps from previous overhauls, they boing like those sprung door stoppers when you flick 'em....]
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If the op-amp is working, but still no send signal going to the pan, then start looking for a cracked trace (really thin boards on these, traces can crack really easily), or broken ribbon cable or jumper (from too much board flexing if it’s been worked on a lot). Heaps of interboard jumpers that can break on those. Give each one a good wiggle with needle nose pliers. Good luck.