Peavey Bravo 112 - reverb fail

[Peavey112Bravo]

Hi all,

so I was walking past a second hand store recently and spotted a guitar amp, which turned out to be a very sorry looking Peavey Bravo 112. I assumed it was dead as it really looks like it's been stored in a shed for 10 years. Anyway, I brought back my guitar and checked it out (one of the knobs fell off whilst doing so) and my god it sounds amazing. I paid £45 for it and practically ran away.

Having cleaned it up, it appears to be in perfect working order, except for a few things:

The reverb is dead. I took out the tank and it's all good. Both resistors register correctly (higher one side, lower on the other) springs are ok, etc. Not sure what else I can check here? Valve in position 1 (closest to input jack) is dead I think. With it on and warmed up, a light chopstick tap generates sound from the speaker. That's about the end of my knowledge on testing valves unfortunately. Does the reverb output go via this valve to be re-amplified and is that the problem? I'm going to change the valves anyway, but would be good to know if I need to check anything else.

Also to change the clean pot, does anyone know what / where I can get a replacement? The whole spindle has gone, so nothing to attach a knob onto.

Thanks.

[Mickey]

Unless you are familiar working on high voltage guitar amps I would respectfully suggest you take it to a reputable service tech/repairer ! These amps have lethal voltages inside so leave it alone !

[TomCarlos]

Attaching the Bravo 112 schematic....

As Mickey said, unless familiar with electronics and safety, take the amp to a trained technician.

Peavey Bravo 112 Schematic - PV_Bravo_112.pdf

[Mick Bailey]

The reverb is solid-state. The first thing to check is the foot switch socket contacts - if these are corroded/oxidised the reverb will not work.

Pots for these amps are difficult to find in the UK and you may need to adapt something else.

[Peavey112Bravo]

Thanks all. Yes, I am very aware of the risks, but always worth reminding everyone that reads these. I'll take another look when the valves turn up and report back. Thanks for the schematic too.

[The Dude]

......The reverb is dead. I took out the tank and it's all good. Both resistors register correctly (higher one side, lower on the other)......

What resistors are you referring to here? Are you talking about the transducers in the tank or something else? If transducers, be sure to also check cables. I will usually check the tank transducers on the amp side. That way you check cables and transducers at the same time. You could just have a bad cable.

[TomCarlos]

My guess is that PV112B is referring to the transducers.

The schematic is hard to read, but I believe the reverb tank is the 710-11114 part number. That is the standard Acutronics 4EB2C1B tank. Please make sure someone did not swap out the tank for something else.

I have a spare tank here.... The input dc resistance measures around 90 ohms and the output measures around 220 ohms.

[Peavey112Bravo]

Hi again - yes I was referring to the tank transducers. I got new valves today (complete set) and the one that appears to drive the reverb tank (if I've read the schematic correctly) is now good, but still no reverb. I need to check the cables too and re-measure. And yes it is the Acutronics and it's the original. I'll post back when I get a minute.

[g1]

I got new valves today (complete set) and the one that appears to drive the reverb tank (if I've read the schematic correctly) is now good, but still no reverb.

No tube is driving the reverb. The reverb circuit is all solid state (post #4).

Have you tried a footswitch or checked out the footswitch jack?

[Peavey112Bravo]

Thanks for that. OK, so it's a bit more obvious what the problem is now. The Op Amp is not on the board!! It's been removed. So this may be a dead-end - not sure that is going to be a part I can get (4558 in the schematic above).

[g1]

RC4558 or NJM4558 are common and easy to find. Just make sure you get the DIP package and not the surface mount type.

[Peavey112Bravo]

Great thanks - is that pin 8 under U1A and 5 above 6 on right of U1B? That seems to match the specs of what I can find as potential replacements.

[g1]

Yes. All DIP versions of 4558 use the same pinout.

[Peavey112Bravo]

Thanks g1, I've ordered a replacement. Can you think of any valid reason why someone may have removed the op amp in the first place?

[g1]

Can you think of any valid reason why someone may have removed the op amp in the first place?

I can think of a couple reasons, but can't think why they would not replace it unless they did not use reverb at all.
It may have been defective in a way that was pulling down the -27V line, which would mess up the bias. Or they were trying to troubleshoot a no-reverb or noisy-reverb issue and gave up.
If you still have no reverb with the new IC, the next places to look would be the footswitch jack, then the Q1 Fet,.