Peavey Classic 30 Squeals Like a Pig

[misterc57]

Picked up a Classic 30 combo.

Squeals like crazy after tubes warm-up. All volume and gain pots set to zero, reverb at zero, EQs at mid point.

Pull out chassis. I noticed 2 of the 3 22uF caps were physically leaking on the positive side.
I had 3 new 22uF 500V available, so I replaced all 3 of them. Also repaired a broken jumper wire that goes from board to board. All other jump wires look good.

Inspected board for bad solder joints, all look good.

I was hoping this would fix it but it still squeals.

The 2 2200uF caps look like they may have been replaced at some point. The 2 47uF caps look original and look ok.

I noticed that CR4 has been replaced with 2 diodes in series.

I swapped all 3 preamp tubes, still squeals.

I am powering up on variac with bulb limiter. Once warmed up she squeals. If I move variac voltage up or down, I hear a pop followed by the squeal.

Time to visit the forum and ask for help!

Thank you, Marko

Will attach schematic and pics in next post.

[misterc57]

The pictures are before I installed the 3 22uF caps and fixed the jumper wire (located next to R66, the 15 ohm 5W).

R66 legs looked burnt, I scraped them clean and read 19 ohms. Underside chassis of R66 is clean. You can see the jumper wire has a break, that I fixed.




Classic 30 schematic.pdf

[nosaj]

The pictures are before I installed the 3 22uF caps and fixed the jumper wire (located next to R66, the 15 ohm 5W).

R66 legs looked burnt, I scraped them clean and read 19 ohms. Underside chassis of R66 is clean. You can see the jumper wire has a break, that I fixed.


[ATTACH=CONFIG]52168[/ATTACH][ATTACH=CONFIG]52169[/ATTACH][ATTACH=CONFIG]52170[/ATTACH][ATTACH=CONFIG]52171[/ATTACH][ATTACH=CONFIG]52172[/ATTACH]

[ATTACH=CONFIG]52173[/ATTACH]

Just on a whim do you know if the OT was replaced? If so the primaries could be reversed causing the squeel.

None the less I would Christen this the amp the Deliverance model

[Enzo]

If it doesn't blow fuses, then get rid of the bulb tester. Running an amp on the bulb can indeed make it unstable.

Zero your guitar volume and plug it into the FX return, does the noise continue or stop?

I don't care it it is on zero, unplug the reverb pan anyway. ANy change?

[nickb]

I suggest you pull V3 to see if the problem is related to just the EL84's or not.

If that doesn't stop it, then I've heard dying a EL84 tube make a squeal on more than one occasion so it would make sense to eliminate them. The quickest way is to replace all four, if you have spares, just to see it it helps.

<Ignore this next bit as it won't work due to the series EL84 heaters: If you don't have the spares, pull all but one and then replace it one at a time to try to isolate to one bad tube. Often tapping the bad one can make it better or worse.>

If pulling V3 does help, then we should check that the FX return jack is not bad and causing the input the V3A to float and pick up unwanted signals. Check the DC resistance from C31 where it connects to the return socket to C27 where it connects to the FX send socket. If that is high resistance then clean the contacts of the return socket to fix the issue.

That's probably enough to try for now.

[Enzo]

Nick, remember the heaters in the C30 are wired in series. You have to have all four EL84 in place for any of them to function. Same with the preamp tubes, pull one, they all go dark. In this case, pulling V3 does indeed eliminate the preamp.

[nickb]

Nick, remember the heaters in the C30 are wired in series. You have to have all four EL84 in place for any of them to function. Same with the preamp tubes, pull one, they all go dark. In this case, pulling V3 does indeed eliminate the preamp.

Yes, indeed they are. I did forget. Thanks.

A common Peavey tactic to make life hard!

[drewl]

Is it the Ned Beatty special signature model?

If so, that's normal.

Check for loose or broken connection, especially between boards.

[misterc57]

Deliverance is still squealing

Thanks for all the suggestions. Still squealing.

Here are things I tried.

Reverb pan disconnected from board.
Bulb limiter no longer being used.
Swapped all output tubes.
Plugged guitar (volume at zero) into FX return.

Regarding the OT. Not sure if it is original, but I read the following resistance;

Primary Brown to Red 74 ohms
Primary Blue to Red 100 ohms

Secondary White to Black 1.2 ohms
Secondary White to Black 0.9 ohms

Regarding C31 to C27 resistance, I cannot get to C27 until I pull the boards out again.

Here is what I see. Once the tubes warm up, I see the current rise and the squeal starts. I immediately lower the voltage to zero.

I like the Deliverance reference!

[glebert]

Are you using the internal speaker? Is it stock? I think stock speaker is 16 ohm, just wanted to make sure someone didn't put a 4 ohm in or something.

[misterc57]

Yes, 16 ohm stock speaker is in there.

[misterc57]

More observations.

Amp is drawing .5 amps when warmed up. Tried just the external speaker output and it also squeals.

[nickb]

Thanks for all the suggestions. Still squealing.

Here are things I tried.

Reverb pan disconnected from board.
Bulb limiter no longer being used.
Swapped all output tubes.
Plugged guitar (volume at zero) into FX return.

Regarding the OT. Not sure if it is original, but I read the following resistance;

Primary Brown to Red 74 ohms
Primary Blue to Red 100 ohms

Secondary White to Black 1.2 ohms
Secondary White to Black 0.9 ohms

Regarding C31 to C27 resistance, I cannot get to C27 until I pull the boards out again.

Here is what I see. Once the tubes warm up, I see the current rise and the squeal starts. I immediately lower the voltage to zero.

I like the Deliverance reference!

The plug into FX return jack test eliminates the stuff just prior to the fx send. Could you hear the guitar above the squeal?

Please pull V3 as previously directed. This will narrow it down further.

The test required on the OPT was to swap the brown and red leads. Please give it a go.

Did this just suddenly start happening. Was there any repair attempted before it happened?

[Pedro Vecino]

You can cut a pin (previously soldered on top to facilitate its later connection) of C36 capacitor. Itīs a 22uF electrolytic located next to the pair of 100 Ohm/5 watt resistors (accessible without disassembling the boards). That way you disconnect the feedback.

[misterc57]

OPT and wiring

The squeal is so bad and piercing that I have yet to leave it on and try a guitar.

I bought the amp knowing it had this issue.

I now suspect that the OPT may have been replaced because all 6 wires at the molex connectors have heat shrink. Looks like they were spliced.

I had the following readings from the OPT when I pulled the molex connectors off the board.

Primary Brown to Red 74 ohms
Primary Blue to Red 100 ohms

Secondary White to Black 1.2 ohms
Secondary White to Black 0.9 ohms

I cannot get a stable reading on the primary from Brown to Blue. Should I be able to? The reading keeps jumping around.

On the primary the red is the center tap. I looked at some pics online and the wiring looks the same, with red in the middle of the molex connector.

Does it matter which way the primary molex is connected to the board? I would think not but a pic I saw online was reverse of the way mine is connected.

Attaching some images.

Thank you. MarkO