Peavey 130 Hum

[kcellwood]

First post. I have been monitoring for awhile though. I bought a new Peavey Special 130 back in 1986. Upon firing it up recently I found it has a lot of hum on both channels. This amp has sat idle for years. I also remember years ago seeing a puff of smoke come out of the back but it never really seemed to affect the amp as far as I can tell. Can't remember if it was humming back then. Based on what I am reading here I am going to start by changing 4 of the caps.
According to the specs two of the caps are 4700/50 and two are 1000/35. When I open the cabinet is see that the two caps are actually 4700/55. As stated I am the original owner so I know the caps are original. I do not see any signs of burning from the puff of smoke noted earlier either. My question is can I replace these 55 VDC caps with 50 VDC caps? Can't find 55's.

[52 Bill]

If the originals were rated at 50 volts, a modern 50 volt replacement should work just fine.

On some older Peavey amps, the style of cap that they used will be hard to find, so you may need to do a little adapting to wire the new caps in place.

[Enzo]

Says 50v on the schematic, and the power rail is 42v, so 50v caps ought to work fine. 55v is an odd value, not standard, though PV used 55v caps for years. The simple solition to 55v caps is to go up to 63v caps which IS a standard value.

[kcellwood]

Received my 4 caps today and have them installed. Amp is quiet know. Thought maybe it wasn't working when I turned it on it was so quiet. The "pop" is also gone when I turn it off. I can just barely hear it powering down now. Thanks for all on this board for all the info.

[kcellwood]

Well so much for the repair. After about an hour of playing at a very, very low volume one of my 35 v caps popped. Blew the + end right off it. Noticed that the other cap was quite warm. They were wired correctly. Any ideas? When I pulled the old ones out there was no visible damage.

[Enzo]

What is the health of the rectifiers feeding it? If AC is getting to the caps, they will indeed rebel.

[kcellwood]

Enzo, what is the best way to check the rectifier? I am by no means an expert in electronics. Would one or more of the diodes be bad? How do you check them.