peavey 6505 + 112 lead channel noise / previous board repairs.

[timgman]

I'm working on a 6505 plus 112 that has a "squeal on the lead channel. after trying some spare known good tubes the issue persisted.
I opened up the chassis and found that someone had made a previous repair or mod around the 4th pre tube. I was wondering if you guys might be willing to look at some pics and help diagnose the issue.
Also should this repair fail, could the parts be used in another amp project?

FYI:
I've drained caps in my valveking my tsl 100 and mesa nomad.
I do know the process to safely work on this. If I have the ability or if it's possible to repair this is another subject.

[lowell]

Could you please post a schematic so we can better assist?

[timgman]

Here are the schematics.

Could you please post a schematic so we can better assist?

6505112.pdf

[timgman]

I'll take some Pics of the previous "work" later tonight.

[ThisLifeILead]

i hate working on these amps. I have had two friends bring me there 100watt 6505+ heads after a retube saying its noisey and squeels at certain settings... and these amps are 20 gigs and 2-3 yrs old. i couldnt find anything really wrong on one but one had a cold solder on a coupling cap around v4. just be very careful as those pcbs are very easy to damage when heating up.
the noise could very well be related to the previous work and my guess is the previous person had lifted a trace and ran a few wires to make up for it. check the solders on the previous work.

[lowell]

Ok. Please be as specific as possible about the squeal.

Squeals at high or low volume....or both?

Squeal is dependant on control settings and if so what settings?

Squeals ONLY when guitar is played and is related to signal. Or does it squeal when nothing is plugged into the input?

When the squeal happens, does a WHACK with your fist on top of the amp change or stop the squeal?

[timgman]

The squeal is on both channels, it's only there with the guiatr plugged in(I'll need to verify this a second time) . It gets louder as I increase the volume pre or post.
here are some pictures of the areas that had work done.

Off board repair?


I see a Cut trace after r36!!

[timgman]

BTW, I had a tech "touch up a few solder joints" He told me that worse case scanerio, maybe I could use some of the parts for a ptp project. lol

[52 Bill]

Is this your amp or is it owned by someone else? Are you trying to fix it or are you just trying to stop the squeal?

When I see work like this, I usually assume that this was modded to sound more awesome and that there was a lot of swapping in and out of parts to find the ideal values. If this was in fact the case, I compare the circuit to the original schematic and find out what was changed in order to see what might be causing the squeal.

You could just remove all of the mods and make it stock, or try and find the website that the mods came from. Once you know what has been changed, it will be a lot easier to understand why it might be oscillating.

[g1]

Good point. If it's been modded for extra gain in the lead channel, that would sure help it squeal earlier.

[timgman]

This is my amp. when i tried it out (and bought it from the con-artist that sold me it) the clean worked and the gain channel was noisy. after a few attempts at swapping preamp tubes I let it sit for a month or so..
after which I powered it up and it had a harsher oscillating tone on both channels. Now, after I got it back froma local guy, it just sounds like 90% static and 10 percent guitar signal ;(
the first part is just a fix above the board. the second part where the trace is cut? who knows. I'd say it's just a lost cause. ;(.
I tried the effects return and it would seem the issue is in the power section because the crackle is still there. . but who knows.

[52 Bill]

I'd say it's just a lost cause. ;(.

This should be far from a lost cause. You can have the circuit restored back to original and have whatever the problems with it fixed as well. If you can't do the work yourself, I would guess that you should be able to find somebody that would be willing to take it on.

I guess that you could always sell it as is to somebody that wants to work on it himself.