Uncontrollable feedback

[Merlinb]

Did you check your Negative feedback loop ? Make sure nothing is open.
I don't see the cap across the PI, not that it is necessary.

That cap stabilises the feedback loop against variation in OT design. I would put one in there, maybe bigger than usual, say up to 220pF. (Don't worry, that's not big enough to kill the highs)
Actually a more reliable way to do it is to put a 100pF to 150pF cap in parallel with each power valve grid leak. (the M3sa Dual Recto does both!)[/quote]

[Merlinb]

Lousy error messages.

[skyboltone]

Did you check your Negative feedback loop ? Make sure nothing is open.
I don't see the cap across the PI, not that it is necessary.

That cap stabilises the feedback loop against variation in OT design. I would put one in there, maybe bigger than usual, say up to 220pF. (Don't worry, that's not big enough to kill the highs)
Actually a more reliable way to do it is to put a 100pF to 150pF cap in parallel with each power valve grid leak. (the M3sa Dual Recto does both!)

[/quote]The design he's working from should work fine without snubbing the grid leaks. He's got a lead dress problem. Or as the Rooster says, something amiss in the tone stack grounding.

I'm intending on the TW build currently on the bench to "fix" my presence control and put a 100k variable resistor pot in series with a 50K resistor on the grid load into the clipper stage. Put that in the Presence hole.

[Trigger]

I re-wired the grounding scheme to buss wire on the pots, moved the jumper from the .1 coupling cap to the phase inverter to the front of the board, and the amp is alot more controllable. With the amp in the low ("gradual") gain setting I can run the airbrake up to the highest setting and she is manageable. In the high ("fast") gain setting, at the highest setting on the airbrake, I have to mute the strings or she will feedback pretty well. I am thinking this is typical for this much gain. Anyway she is not perfect but she is much closer. A better 12ax7 in V1 and I believe that will help quite a bit. Thank you to all that have helped me out on this. I appreciate it more than I can say.

[Merlinb]

The design he's working from should work fine without snubbing the grid leaks. He's got a lead dress problem.

The loop should be stable irrespective of layout (apart from gross layout faux pas of course).
Chopsticking wires until an amp stops buring out your voice coil is hardly a concientious attitude

[billyz]

Have you tried a different guitar? Sometimes pickups are the fault of too much feedback.

[Trigger]

Have you tried a different guitar? Sometimes pickups are the fault of too much feedback.

I plugged my G&L ASAT in tonight and drove the family out of the room by the high pitched squeal. I moved the head off the speaker cab and didn't help. My Les Paul does not get as much squeal, but the pickups are a pretty hot set and could be some of the feedback issues. I will go over her again tomorrow. Hopefully I'll see something I've been missing.

[billyz]

G&L 's usually have pretty good pickups. mine never caused any squealing and was not overly microphonic. I would look again at your presence control circuit. Does it affect the squeal, where do you have it set?

[rooster]

OK, you are almost there. Replace the .1 cap on your Presence control - do not use a cheap-arse cap here - and recheck all connections to this pot from the 10K resistor to the Presence control ground. Copy the Kelly pics, BTW.

Finally, if this is no help, your split load resistor network from the Komet circuit may be fubar. Are you sure you did this correctly? If the Presence control is not your problem, this is where I would go next. You may have created a home for some parasitic oscillation here. Its not really clear how well you executed this circuit from your photos but since you are hybreding things this could be a problem area. Basically anything out of the ordinary needs to be looked at if your problem continues.

FWIW, sometimes it is best to build anything, whatever it might be, and add the extras onto it. This is especially true if you are building a high gain circuit I think. But I get the go-4-it attitude, sometimes it works.
So in other words, if all else fails, maybe you should remove the additions, confirm stability, and try adding the bells and whistles then?
Anyway, best of luck.

[Trigger]

I will take a look at the presence circuit tonight. I already removed the split load switch but did not have time to try it without it yet. Again thanks for the help. Eventually I hope to hear this thing sounding like it should.