Peavey does and would send it to you if you asked them for it.

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We don;t know the preamp works.  All we know is that some preamp controls affect the signal.  The distortion controls may work, but that doesnl;t tell uss that the outp-ut IC from the preamp is OK.

You have FX loop jacks, use them.  Plug the guitar into the FX return.  Is that strong and clear?  Or weak and muffled?   And likewise, send the signal from the FX send to some other amp and speaker for a listen.  Same Question, loud and clear or weak and muffled?

Turn the reverb up at least midway, then rock the amp to crash the reverb springs.  Does that come out loud or does that sound weak?

And if it is the power amp, have you tried more than one speaker cab?  There is a 0.27 ohm resistor between the sleeve of the speaker jack and ground.  If that is open you get very low output - check that resistor and its connections.  And for that reason, check the speaker jack itself and its solder.

I have no photos of when I did it.

What is the exact name on the schematic?

Is your loud squeal high pitched, like an infant screaming?  Or is it a loud BRAAAZZZZZ like you were touching the tip of a guitar cord with a finger?  Look at the speaker cone, does it move one direction and stay there?  That would mean DC on the speaker, check with a meter.  Not good for the speaker by the way.

Disconnect the speaker, does that part still get hot?

I am looking at drawing 99010700 from 27 feb 2001.  See the headphones jack?  Right next to it on the schematic is 22 ohm R149.  Is it open?  On the board it is right near the phones jack also.  That resistor is part of the stability network.

Perhaps you missed my suggestion.  That cap may be hard to get at, but its terminals connect to other things.  SO if I cannot get at the lead of a cap directly, I look in the schematic for the resistor or transistor or whatever that connects to it.  I then can connect my probe there.

The reverb I am familiar with is Piezo at both ends.  If there are other formats Silvertone used, I just am not familiar with them.   If there is a god in heaven, then SIlvertone didn;t make ALL their reverbs with that piezo.

The infamous SIlvertone reverb assembly I know was based on piezos, so good luck measuring transducer impedance with a meter.  They stretched a piece of spring down the body, then they had a small clamp near each end with a hunk of piezo wedged in it.  The piezo stuck up between windings of the main spring.  One piezo was driven, so it vibrated the spring.  The other end acted as a pickup.  I suppose in thinking about it, it didn;t much matter which end was which.

I am not sure the existing drive circuit would be happy with even the highest impedance conventional pan.  Maybe.

I managed to rebuild a couple of them.  I got a piezo element and stuck pieces of it in there.  Be aware that the piezos they used were two sided.  So the two sides of the clamp were the two connections for the piezo piece wedged between them.  The common piezos I find, like the ones in the Motorola tweeters are sandwiches.  There is a central disc, with piezo on either side, then outside contacts are wired together.  SO the two sides are the same electrically, and the second connection comes from the center disc.  SO you cannot just stick one of them in the old clamp without modifying it.

You won;t hurt it, if you turn up too far, you wind up clipping.

And contact Samick and ask them if they can provide the schematic.

I am a professional technician, I work on this stuff all day long.  I have to say that getting board extensions is really working extra hard to take the easy way out.  I almost never extend a board from its chassis.  I will free them from their mounts and flip them over onto a towel or something if I need to get at the far side while running.  But mostly I operate with the boards in place.

If I need to get at the pin of some socket that is covered, I look for the components that connect to the socket pin.  There is bound to be a resistor that goes where you want to be.  So I find R123 or whatever and probe its lead.

The only times I need an extender are instances like a little DSP card covering the area of the main board I need to service.  Or card racks where several boards are lined up side by side.

Well, no WONDER it sounds OK.  You replaced all the red knobs with black ones.  Of COURSE it sounds good now.

You are not measuring them with the amp on are you?   If your ohm meter goes backwards, that means there is voltage in the circuit.  Flip it to volts and see.   At worst, unsolder one end of each resistor and lift it up to measure it.

Stick with the stock MPS6530/6531.  It is what the amp is designed around, all MPS6531 will have the same EBC pinout. Mounted flat side away from the drivers. I can't speak for the 2N3642, I don't know what package they are in.

Those are limiters, the amp should work fine if you simply remove them.  Of course that would also remove some of the amp's own protection.

Like any limiter, they turn on when their base is energized.  Look at the circuit.  When the voltage across resistors R155, R159 gets large enough, the transistors turn on and ground off the signal at the base of the drive transistors.   And what causes that voltage in R155, R159?  Current through them, the same current flowing through the tubes.

SO the question arises, have you put different tubes in it?

And for that matter we could have a failing drive transistor, or two.

And look at those resistors, they are the two 5 watt resistors next to the drive transistors.  DO both measure 3 ohms?  And is the solder to each in good shape?

Measure the voltage across each resistor, does it meet the spec on the schematic?  20-40mv each?  And when it fuzzes out, do those voltages change?

I thought I mentioned this earlier, but now that you know it is the switch, look CLOSELY at the switch.  The way the switches are usually constructed is the metal frame has little tabs sticking out the bottom, and those tabs are bent under the little piece of material that holds the contacts and terminals.   If something smacks the little knob, it can push out the back of the switch by bending those tabs.  Then the switch will no longer work.  Sometimes such a damaged switch can be saved by putting it back together and bending the tabs tight down with pliers.

At this point, what is there to lose?  The switch is coming out one way or another anyway.

And switch or no switch, if you want to play the amp while waiting for a new part, temporarily tack solder a little piece of wire between the switch terminals to complete the circuit.

Peavey is great about having parts for their products.

Whether or not it is the case for your switch, that same sort of pushing out the bottom damage happens to sliders on m,ixers all the time.  Most times they are easily repaired.

OK, as expected then the amplifier works, just the signal is not making it through the output jack board.

You clipped to the yellow and blue wires and got sound.  Leave the blue wire clip in place. now remove the other clip from the yellow wire, we will be using the test speaker now as a signal tracer.  Follow the yellow wire over to the jack board.  See where it connects to the jaqck boad through a plug.  Touch the clip to the terminal that gets the yellow wire.  SOund?  Move teh clip wire to that 5.6 ohm 5w resistor next to the coil of wire.  Touch it to each end.  GOt sound at each end of the resistor?   

At this point the sound goes to the impedance switch for routing through the output transformer.  At 4 ohm setting the switch directs it to the jacks directly.  But it DOES still go through the switch.  A bad switch or a switch with bad solder can still interrupt things.

With the jack board sitting so you can access the solder side - dismount it from the chassis if you need to - look at the end connection of the coil of wire and follow the copper trqace to the end of the switch.  Also note the middle terminals of the switch have a trace to the jacks.  The switch must connect these two together for sound to happen.  So touch your clip to the end terminal of the switch, the one from the coil of wire.  Now touch to the center terminal of the switch, the one with the L shaped copper trace that feeds to the jacks.  Got sound there?

What we did was use the speaker with one end connected to the blue wire, and stepped point by point down the path to the output jacks.  Once we find the point that has sound on one side and not the other, we have discovered the break.   My money now rests on the switch.