Twin Reverb Reissue with Reverb on Normal Channel

[sluckey]

Try a 12AU7 for the reverb driver. Hum any better?

[sonicmojo]

Try a 12AU7 for the reverb driver. Hum any better?

I had tried a couple of different tubes before and no help, BUT....

Issue is solved! No more reverb on Normal channel and no more hum.

It was actually the 22uF filter cap C32 for sure. The cap has the connection to the "Z" on the schematic which went right to the reverb driver and I guess the lack of operation there let some things bleed through from the other channel. The cap had no capacitance when I measured it out of the circuit but was not shorted. I also replaced C33 which was the other 22uF in the doghouse but I think that one was okay.

I may go ahead and replace the rest....

Thanks for all the ideas and quick responses guys!!!!!!

[martin manning]

Great! Must have been feeding back from the screen, I think.

[sonicmojo]

Great! Must have been feeding back from the screen, I think.

Interesting.... So you think it was a feedback loop from the first power tubes filter node that was unconnected and possibly moved down the line to the other nodes? The reverb did not sound nearly as good coming from the normal channel, kind of raspy but VERY apparent, about 3/4 strength.

[Stevem]

Step thru the normal circuit up to the PT with a set of headphones protected with a blocking cap , or couple the outputs to another amp to see / hear where the reverb is joining in.
That amp as you know should only have the verb on one channel.
Be careful that the high audio levels do not blow out your headphones.

[martin manning]

I’m thinking the leak had to be entering at the reverb driver for the reverb to be as strong as it was, and that tube is powered from that node with the bad cap. The only signal present there would be from the screens.

[sonicmojo]

Step thru the normal circuit up to the PT with a set of headphones protected with a blocking cap , or couple the outputs to another amp to see / hear where the reverb is joining in.
That amp as you know should only have the verb on one channel.
Be careful that the high audio levels do not blow out your headphones.

I hear you, I only usually trace the signal in really rare circumstances. Amp is returned, Working well so all is good! I still don't really like these reissues. I wish they would have at least left a little bit of leads on the caps sticking up from the PCB but these were all tight. Makes it hard to even trace a fault considering the design and overboard placement of the components on that PCB. I'm glad it is working again. I always like to save a tube amp even if it is not worth the time in certain cases....