I've been swapping two different 6V6's through the amp. The values are a little piecemeal as I've been going for gross characteristics. Doing all the measurements with the 6V6 in it at the moment, I get:
401V plate to chassis
375V plate to cathode
25.82V cathode to chassis
36.6mA plate current
finally, the cathode resistor is 2x330ohms or 660ohms
champ 5f1 clone -- sudden loss of volume
Moderators: pompeiisneaks, Colossal
Re: champ 5f1 clone -- sudden loss of volume
I'm on board with calling those numbers fine too.
The v1b signal at "low volume" looks like it's maybe 17vac if i'm reading your scope right. That should be plenty enough signal for almost full volume coming out of the speaker, if everything else in between was also fine.
You already said the signal at the 6V6 grid is good, and that leaves the OT and its leads as the nearly the only things left to suspect.
I say nearly because if there's any high freq oscillation happening on the 6V6, the screen grid could be part of that. But at this point oscillation feels like a "hail mary", on the chance the OT is still good.
The v1b signal at "low volume" looks like it's maybe 17vac if i'm reading your scope right. That should be plenty enough signal for almost full volume coming out of the speaker, if everything else in between was also fine.
You already said the signal at the 6V6 grid is good, and that leaves the OT and its leads as the nearly the only things left to suspect.
I say nearly because if there's any high freq oscillation happening on the 6V6, the screen grid could be part of that. But at this point oscillation feels like a "hail mary", on the chance the OT is still good.
Re: champ 5f1 clone -- sudden loss of volume
Yes, I agree. Adding a grid stopper or small value ceramic cap from the grid to cathode on the 6V6 are things I'm trying before the OT shows up, but I don't have much faith at this point that the issue is an oscillation.
Re: champ 5f1 clone -- sudden loss of volume
The new output transformer showed up in the mail today. I subbed the new transformer in for the old one, and... voila... the champ clone is functional once again. I'm just happy it's fixed as I tend to put other things on hold while troubleshooting.
The scope trace with injection of a 1KHz signal went from this on the 6V6 plate: .
to this:
The scope trace with injection of a 1KHz signal went from this on the 6V6 plate: .
to this:
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