Peavey Classic 30 - Speaker Short

[Shawnobi]

Hi Folks,
The speaker connections on my girlfriends C30 got shorted together after a house move

The amp powers up quite happily however there is no sound. Can anybody give Me a few pointers on where to start looking? I thought there may be a fuse on the output but can't see it.

When I put my meter on each speaker lead they both give continuity to ground.

[Jazz P Bass]

First off: Do not operate the amp without a good speaker.
Remove any one of the amp connections to the speaker.
Measure the resistance of the speaker. (16 0hms)
If the speaker is good then you need a tech.
The amp output wires are the secondary windings of the output transformer.
They will read a very low resistance.

[Amp Kat]

Speaker is either good or bad. If you measure across the speaker leads from positive to negative it should read it's load value in resistance so the C-30 original Blue Marvel is a 16 ohm speaker should read about 15.5 ohms. Being the output transformer is grounded on one side you will read continuity to ground. There is 3 fuses on the C-30 and two are inside `on the main board and are the heater fuse which is a 10 amp ceramic and the HT fuse which is a 500ma. The mains fuse is in the back and may be outside too as I can't remeber but want to say it may be inside. If the speaker is shorted across it's terminals it is likely bad.

[Shawnobi]

Thanks for the replies. Speaker is good. Let Me just clarify what happened.
I got a call from my Girl at rehearsal saying there was no sound coming from the amp. When she brought it home, both of the speaker connections were off and touching the metal cage of the speaker. So I don't know if these were shorted when she powered up, or if they were not touching anything. Either condition bad I guess.
So,
Speaker is confirmed good.
All fuses are fine.
Both of the speaker wires from the amp show continuity to ground with a meter.

[Shawnobi]

Any thoughts on this?

[Jazz P Bass]

IF the amplifier was running into a dead short, that may have taken out the output transformer.
Maybe, maybe not.
In any case, you need to take it to a tech.

[Amp Kat]

When measuring across the secondary of the OT you will read very low ohmage so since one side is going to ground you will read 0. ? ohms from either to GND and is fine.

[Shawnobi]

It's ok, I'm perfectly happy to safely prod around inside the amp myself. I rebuilt the thing from a smashed up mess. Kicked in speaker, burned out PCB, snapped off pots. It was horrific. Looks lovely now though. Just a little quiet all of a sudden

I'll whip out the output transformer and check the windings as a starter for 10. If any experienced chaps can point Me towards anything else which may have suffered damage from such an incident I would be greatful.

[52 Bill]

This is a tube amp right? Not having a load connected can damage the OT, shorted output probably no problem.

Pull the wires off and test the speaker with a 9 volt battery. Does it make noise? If yes then hook up the speaker and turn on the amp. Do you hear anything? Hum? Hiss? Rattle the reverb tank, any sound? Are the tube filaments lighting up?

[Shawnobi]

Hi Bill.
Speaker ok with 9v test.
All tubes have a gentle healthy glow. Only noise coming through is a bit of reverb feedback from the tank (reverb knob controllable). No clanging from giving the tank a light knock.

[52 Bill]

OK, now you are getting somewhere. The speaker is ok and the output transformer is probably ok as well.

Does this amp have an FX loop or power amp in jack? If it does, plug an instrument in to the return side and listen for sound. Anything? Continue forward stage by stage and try and see why there is no output. Does turning up any of the controls (tone or volume) change the sound of the hiss and or hum at the speaker?

If you rebuilt this thing once before, you should be aware of the ribbon cable failure problems with these amps. You may need to check them as well as the tubes.

[Enzo]

Oh, don't guess at it. Speaker works. OK, are ALL 7 tubes lighting up? This is important on this amp due to the series heater wiring.

Go to the power tubes, B+/screen present?

If missing, remember that the fuses in this - and most amps - must be removed from their clips for testing.

[Shawnobi]

All 7 tubes light up. Good point on the fuses, I shall pull them and check. And will also check the B+/ Screen.

[Shawnobi]

Hi everyone. Apologies for the late reply, we have 2 darling 6 month old babies who have reduced my tinkering time!

Just to recap. This Classic 30 has no sound, possibly after a speaker short. All fuses are good (removed and tested). Power comes on and All tubes light up.
I've just removed all the power tubes and done a voltage check comparing them with values i took when I rebuilt the thing last year. It seems none of the power tubes have the -16VDC at pin 2 (Bias voltage?). All other voltages were healthy.

Can somebody point Me in an onward direction?

Thank you.

[Jazz P Bass]

Peavey Classic 30 bias voltage

Here is the Classic 30 schematic.
In the lower left corner is the power supply.
You can see where the "bias" is notated.
First item is F3. Is it good.
I would check (unit off) the resistors associated with the bias voltage, after the -36V.
If all is good, power the unit & see that the -36 is there.
Also see if the -15V is there.
If both are missing the bridge rectifier will have to be checked.