Intermittent Voltage drop in SF Super Reverb AA1069

[vmazz]

I’m working on troubleshooting a super reverb silver face aa1069 circuit. It intermittently gives off a horrible dsitortion and volume drop. It didn’t show up for a couple days but that’s what the customer complained of. Observing it on the bench I noticed typical 440v at the center tap of the Output transformer, then when the distortion shows up I get a drop in the center tap voltage to about 210v basically half(and everything else downstream is dropped accordingly) and the B+ voltage at one side of choke goes up to about 510. I’ve tried this without power tubes in and it is intermitten still. I know this must be a component issue I’ve resoldered most of the power section and the tube sockets. What would you assume would cause this intermittent drop?(specifically what could cause the half voltage) I’ve tried chopstick and moving things around and haven’t found anything conclusive.

[Helmholtz]

Please post appropriate schematic.
If B drops to 210V and the mains fuse (correct value?) doesn't blow I don't assume a loading effect.
Is the standby switch good? Try shorting it.
Which side of the choke goes up to 510V?
Please post voltages on either end of the choke with and without power tubes.

[vmazz]

Here is a schematic

[vmazz]

This pic has the voltages when the drop occurs.

[Helmholtz]

Looks as if the choke likes to go high impedance intermittently.

[Chuck H]

Looks as if the choke likes to go high impedance intermittently.

This was my though as well but I didn't want to get in the way of your process here.

[vmazz]

Would this possibly be due to a bad connection at either solder eyelet? Or does this happen within the windings of the choke sometimes?

[R.G.]

Would this possibly be due to a bad connection at either solder eyelet? Or does this happen within the windings of the choke sometimes?

Yes, all of the above.
Resolder/remelt the solder joints to eliminate that possibility.