Hooked up PT wrong on a 6v6 2204 build

[Jasonvilla]

Hi all. I have(had) a working DIY 6v6 jcm800 type amp that I built. Pretty straight forward 2204 circuit with a few changes for the 6v6s. Well it was working fine... but the other day I decided to hook up the 115 primary tap up to see what it sounded like with more voltage and bone head me hooked up the 115v tap and the 125v tap instead of the 115v and ground. Well the fuse immediately blew. I wired it back up correctly and replaced the fuse. Now the amp isn't too happy, but the voltages seem normal. It makes hissy crackling noises, but still plays. I swapped out the power tubes, thinking i killed them,(running jj6v6s) and as soon as they warmed up the amp made weird radio/oscillating noises. Put the old tubes back in. Checked the bias, seems to be fine. Tried checking the tube plate voltage and it immediately starts making that fm/oscillation noise and freaks out my RMS multimeter with flashing display, on one tube. The other tube plate voltage checks out fine - around 425v. If I check the weird tube plate voltage with my cheapy multimeter it makes the noises but gives me a reading of around 425v. Soo Im not sure where to go from here. Any help would be greatly appreciated. Thank you!

[Leo_Gnardo]

Yikes, you put line voltage across 1/12th of the primary winding... I'd expect all the secondaries tried to deliver 12x or so their rated voltage. Filter caps, interstage caps, I'd be looking there for failures. Rectifiers, the main ones & bias too. You can go 10, 20, sometimes even 50% beyond rated voltage on these parts and get away from it, but 1200%, OW! Thanx hevvins for fuses. Hope you get your prize back to normal, I've always liked the concept of low power Marshall style amps.

[Jasonvilla]

Haha well when you put it that way... Thank you so much for the reply! I did replace the rectifier diodes but the bias diode and drop down resistor tested fine. Im also getting the same bias voltage as I did before the incident. So it looks like I should be testing the filter caps? Is that why my tube is turning into a radio? Thank you!

[Justin Thomas]

A lot of those parts may show up okay with the 9V a meter puts on them, but at working voltages, may break down... Just a thought...

Justin

[52 Bill]

So it looks like I should be testing the filter caps? Is that why my tube is turning into a radio?

It might be. Remember that "filter" caps also decouple the power supply. That means keeping the different circuits from interacting through the power supply. If you have damaged a cap it may be allowing the circuits to oscillate.

[Jasonvilla]

Thank you for the advice guys. Looks like Im going to be ordering some parts!

[R.G.]

Experience is what you have left when you've forgotten exactly how you got that scar.

[olddawg]

I doubt if it is rediculously expensive to recap the whole thing. You also might want to turn out the lights and check for arcing.

[Jasonvilla]

Its not expensive, its just a pain and i don't want to do it!

[tubeswell]

Its not expensive, its just a pain and i don't want to do it!

No gain without pain

[g1]

I'll second the arcing idea.

[Jasonvilla]

Where might it be arcing? Thanks!

[g1]

Possibly tube sockets. Like olddawg said, turn off the lights and see.

[Leo_Gnardo]

Possibly tube sockets. Like olddawg said, turn off the lights and see.

Also, pull the tubes, look for scorched, carbonized arc marks on the tube bases AND tube sockets.

There may be intermittent shorts inside film caps too. Not likely you'll see any sparks or anything, just hear fizzles, pops, ticks, like that. Most worrisome if it's the caps bringing signal to the output tube grids - that would raise some hell with the output tubes besides annoying noises.

Examining (carefully please!) the amp's innards in dark conditions could certainly reveal problems. I've found failing resistors at times - in an SVT a preamp resistor was crackling something awful. Looking at the board in the dark, the resistor lit up with blue spiral arcing then it was obvious which one was faulty. You may see similar things going on. Have fun!

[Jasonvilla]

Thanks for the reply. I pulled all the tubes and looked at the pins, as well as the sockets. I didn't see any signs of arcing. I MAY have found a bad coupling cap by taping it with a chopstick. Ill have to replace it and see.
I also turned off the lights and looked around a bit. I also played some guitar through it. I didn't see any arcing. Thanks for the help guys.