EL34 Grid Stopper resistor

[ca7922303]

Put those 100k from orange 16 ohm to old blue point back. See if oscillate worse

I don't believe it to be worse. About the same.

[ca7922303]

Put those 100k from orange 16 ohm to old blue point back. See if oscillate worse

Also, did I need to reconnect the trace that I cut after soldering ceramic capacitor on V6 to test?

[ca7922303]

Also seeing now that the red plating is only occuring on one of the power tubes(V8).

Correction : red plating on V7 & V8.

[Jazz P Bass]

Send it to me.
I will fix it!

[catalin gramada]

Also, did I need to reconnect the trace that I cut after soldering ceramic capacitor on V6 to test?

Those link, together with the wire link you removed from blue/green solders is part of you original nfb circuit. You will need to restore but for the moment you amp is still no stable in open loop. Have no ideea why, is hard without the amp in front...JPB did a nice proposal. Better to handle to him.

[ca7922303]

Those link, together with the wire link you removed from blue/green solders is part of you original nfb circuit. You will need to restore but for the moment you amp is still no stable in open loop. Have no ideea why, is hard without the amp in front...JPB did a nice proposal. Better to handle to him.

Appreciate all your help. I won't be able to send it to anyone though. What do you make of the presence not working in relation to oscillation? Thanks.

[catalin gramada]

I don't even see on schematic where you presence control is, but I may suppose is in nfb loop controlling the amount of feedback injected for certain frequencies. If you have blue/green link removed and those trace still broked all nfb matrix including presence nfb control is disconected. You have to restore the wiring ( installing a U shape wire from green to blue and recover also the broked trace with a short wire from soldering point to soldering point, then will make the feedback presence control active.

[ca7922303]

I don't even see on schematic where you presence control is, but I may suppose is in nfb loop controlling the amount of feedback injected for certain frequencies. If you have blue/green link removed and those trace still broked all nfb matrix including presence nfb control is disconected. You have to restore the wiring ( installing a U shape wire from green to blue and recover also the broked trace with a short wire from soldering point to soldering point, then will make the feedback presence control active.

One last thing if you don't mind, should I leave ceramic capacitor I soldered on V6 pins1&,6 and I'm wondering if that cap was not rated for at least 1kv what would have been the result? Thanks again for your help.

[ca7922303]

I don't even see on schematic where you presence control is, but I may suppose is in nfb loop controlling the amount of feedback injected for certain frequencies. If you have blue/green link removed and those trace still broked all nfb matrix including presence nfb control is disconected. You have to restore the wiring ( installing a U shape wire from green to blue and recover also the broked trace with a short wire from soldering point to soldering point, then will make the feedback presence control active.

Also, presence is on tone board page of schematics connected to damping switch(which isn't working either) near D1 10 pin switch(ribbon cables).

[catalin gramada]

Those cap was supposed to cut some excessive gain in high freq range by cancellation between phases. As time is doing nothing in respect with you problem there is no reason to keep it there. There is allready instaled a 47pf in those position somewhere on board .You osscilation have other origins hard for me to say.You tested empirical almost all possible causes which may generate the instabilities but in a high gain amp even the wiring posing may cause problems, is hard to say where the fault is without to scope.

[ca7922303]

Those cap was supposed to cut some excessive gain in high freq range by cancellation between phases. As time is doing nothing in respect with you problem there is no reason to keep it there. There is allready instaled a 47pf in those position somewhere on board .You osscilation have other origins hard for me to say.You tested empirical almost all possible causes which may generate the instabilities but in a high gain amp even the wiring posing may cause problems, is hard to say where the fault is without to scope.

I have a signal generator and PC based oscilloscope. Would you want to walk me thru tracing oscillation?

[ca7922303]

Those cap was supposed to cut some excessive gain in high freq range by cancellation between phases. As time is doing nothing in respect with you problem there is no reason to keep it there. There is allready instaled a 47pf in those position somewhere on board .You osscilation have other origins hard for me to say.You tested empirical almost all possible causes which may generate the instabilities but in a high gain amp even the wiring posing may cause problems, is hard to say where the fault is without to scope.

If this repair is correct, still no presence or damping control?

[catalin gramada]

Yes , is restored as original. No need to put such thick wires. Some solid wire as a resistor terminal is allright. And you may solder both in a single spot (old blue).

[catalin gramada]

...

[g1]

The oscillation is most likely due to the presence and damper circuit faults, or other faults in the amp. It is not like the amp is otherwise all working ok, it has other problems that need to be dealt with first.
Please direct any further discussion to the actual thread about the amp in question, here: https://music-electronics-forum.com/...-outout/page25