peavey classic 30 problem

[Breausonic]

Hey guys, I've got a peavey classic 30 112 combo 1996. runs perfect no noise hum or anything else for about 30 minutes then all heaters shut off power and preamp power trans does not get hot. Removed board and touched up any funky looking older joints in heater circuit.was looking at mov and .01 caps in primary but when the heaters all go off at once the pilot light stays on Thanks in advance for any insight on this

[oc disorder]

Hi Breausonic , for me the biggest pain in those things..... are those little wire links that join the boards together.
That's my first "port of call" after removing the chassis !

This layout diagram from Black Magic amps is invaluable in the search !

http://bmamps.com/Schematics/Peavey/...c30_layout.jpg


EDIT : think the pilot light is a neon and runs from the mains power input (110v~240v).

The output tubes heaters (filaments) are all in series if one tube is removed they all go out .
They get their supply via R71 & R 72 white "largeish ..squarish" ceramic resistors!
The pre amp tubes are also in series with a dc supply 36v ! Wired as 12 volts tubes (pins 4 & 5) ..i.e. 3 x 12 =36
R 66 to pin 5 V3. V1 pin 4 grounded.

[Breausonic]

Hey oc disorder, Thanks for the reply i reflowed r71 andr72 and the jumpers between the boards in that area both sides of the resistors.I also resoldered the primaries from the switch to mov to power trans input wires. after about 25 minutes a single pop and all 7 heaters go out at once.

[g1]

When the heaters go out, see if you still have AC voltage at the heater winding right at the connectors (between orange leads going to J27 and J28).
Then check between J28 and the far side of F3 (C51 side).

[oc disorder]

I was wondering when it stops you have HT missing also ?
Inside the transformer here in Australia (230v version) there is a thermal fuse just under the plastic cover of the power transformer. Think I had to remove the transformer to carefully unclip the plastic cover. It's a non resetable one here.. maybe if yours has one it's intermittent?

[Enzo]

Then the AC would be interrupted at the secondary leads, easy to access without taking the boards out.

[Breausonic]

Hey g-1 Thanks for the reply. when the tube s shut off, there is no ac at j27 j28.After about 10 minutes it fires back up .about 130 each side ht and 15 on the heater side.I was going to open up the trans and bypass the thermal cutout. Barney

[The Dude]

I wouldn't just bypass it, except for testing purposes. If it is indeed the problem, get a new one and replace it. It's there for a reason and you don't want to start someone's house on fire.

Next, the thermal cutoff is on the primary. First, see if you loose all secondary voltages. If you loose only the filament AC, it's not the thermal cutoff.

[Breausonic]

I just pulled off the top cover on the trans and right over the thermal fuse is a brown spot about an 1 1/2 long going from the thermal fuse down the side of the bobbin.Do you know what part id replace that with. I was just going to bypass it with some 24 bus wire with teflon shield.If it works iil buy you a caucasian. All secondary voltages drop out, pilot light stays on

[The Dude]

If you pull out or expose the existing thermal cutoff, there should be a part number on it or some specs like (arbitrarily) 100 degree C 3A or something of the sort. If all secondary voltages drop out, that could very likely be the problem. You can certainly jumper it temporarily to see if it solves your problem. Again, I'm not fond of leaving it that way.

[Enzo]

Something MADE it get hot enough to do that. Find out what that is before going much further.

[Breausonic]

ill take it out and see if i can read it.Ill jump it and see if it makes a difference.If it works ill see if mouser has them.Thanks for the reply,Barney

[Enzo]

Just unplug the amp and measure resistance across it. It will either be open or have continuity.

[The Dude]

Maybe so Enzo. Maybe not. He says it runs for a while, then he loses secondary output. It may just be breaking prematurely and check perfectly fine cold via meter. That said, I do agree that we need to make sure that the transformer isn't getting overly hot. I would temporarily bypass the cutoff, fire it up and monitor the transformer for excessive heat. Go from there. The thermal cutoff may be bad, or it may be doing exactly what it's supposed to do.

[g1]

right over the thermal fuse is a brown spot about an 1 1/2 long going from the thermal fuse down the side of the bobbin.

Any chance you could post a close-up picture of this? It almost sounds like there may be a cracked wire or connection that is arcing. If that's the case, the temporary jumper across the thermal fuse should not cure the problem.