Peavey Classic 30 - Update

[bbmade]

Amp was brought to me by a music store, very little information on the problem besides "crackling noise".  They had opened it up initially and gave up.

Right now, after doing some work, the amp powers up for about 20 seconds then the pilot light goes out.  Plugged into the current limiter, the bulb gets a little bright as the pilot light goes out, but it is not showing a dead short.  It's tough to check voltages because I can't measure directly on the sockets with this three pcb board design.  I'll have to figure out which little jumper wires might have the voltages I want to check.

What I found after removing the boards and before ever powering it up, was some bad solder on the traces of V7, pins 5 and 6.  The added solder wasdangerously close to each other and there was a lot of potentially conductive materials on the board.  I cleaned everything and removed the previous repair and reflowed some solder.  I checked for continuity on the different traces of the tube PCB for the EL84's, found some intermittent spots and removed the solder and re-soldered then rechecked and they were good.

No signs of excessive heat, all the power resistors are in spec and no signs of bulging or leaks on the IC electrolytic's.  The amp was made in 1993 and the IC caps appear original.

Just curious if this jumps out to anyone with more experience.  I'll keep pondering it.  It just seems to lose voltage after power up for about 20 seconds.  Amp sounds good for about five seconds before fizzling out.

With the shop lights dim the filaments for the EL 84's glow bright but I don't notice filaments on the preamp tubes.  Once the pilot light goes out the filaments on the EL 84's start to dim too.  Just seems to be losing voltage, perhaps in the filament circuit (???).

UPDATE - If I pull V7 and have all other tubes in the amp, it does not lose power.  Making notes of components which are a part of the V7 circuit, will test them next week 

Hope all is well out there, haven't been on in a while.


Thank you,

BB

[Banjan73]

I did a service on one of these a couple of years ago.
The crackling sounds familiar..
What I did then was to change all the electrolytic caps in the PS. Those were originally some shitty chinese ones. I replaced them with mostly Rubycon caps. This amps sounds amazing!!

[bbmade]

I know the amp should get new filter caps but it seems like it’s in the V7 circuit somehow.  I’m already to the point in time where it doesn’t make economic sense to service this amp.  I’m wondering what the diode on the plate of V7 and V5 are there for.  I see the plates are coupled to the OT but, I don’t understand the diodes CR6 and CR4.  I’ll be pondering this until next week when I have time in my shop again.

I did a service on one of these a couple of years ago.
The crackling sounds familiar..
What I did then was to change all the electrolytic caps in the PS. Those were originally some shitty chinese ones. I replaced them with mostly Rubycon caps. This amps sounds amazing!!

[sluckey]

I don’t understand the diodes CR6 and CR4.

Those high voltage diodes (typically 3KV) are protection diodes. They will prevent high voltage flyback pulses from damaging OT, tubes, and sockets in the event that the speaker is not connected.

[BrianS]

Not that it helps at all, but I learned a long time ago that these folded circuit board Peaveys are a time sink and not worth repairing. They aren't made to be serviced at all.  I won't work on them in my shop.
Good luck!

[bbmade]

I believe it.  The store agreed to pay me to try and fix it.  I’m certain I’ll have more time than compensation but, I’m stubborn so it’s at least half my fault.

Not that it helps at all, but I learned a long time ago that these folded circuit board Peaveys are a time sink and not worth repairing. They aren't made to be serviced at all.  I won't work on them in my shop.
Good luck!