A question , if a preamp 12AY7's cathode resister connection was open to ground

[catnine]

I posted asking how long Sprague Atom caps last.
I powered up the amp with the bias rite installed just to see if everything was ok.
I had nothing plugged in the inputs yet when I turned to vol pot up just a bit at times I would hears a crackle throug the speaker so i decided to pull the chassis and take a look thinking perhaps the pot was dirty. I began by checking the resister values just to see where they were and the first one I checked was the 1.5K from the V1 to ground and the resister lead at the ground side popped off so it must have been intermitent. So with nothing plugged in and the amp at idle with no ground on the V1 cathode but just the bypass cap what would that do as far as the 12AY7 is concerned? I repaired the problem the caps seemed ok . Trouble is on this weber 5E3 eyelet board the resisters for the cathode bias with bypass caps on V1 and V2 do not have leads long enough to bend over for a physical joint so at the time I just soldered them to the leads of the bypass caps and right on the edge of the eyelet , apparently they over time even with a good solder joint must have expaned and contracted enough to pop loose. This time I bent a loop in the resister leads and crimped the loop around the bypass cap leads and then soldered them witha bit more slack.

[Enzo]

Won't hurt the tube.

[Chuck H]

+1

If you lift the cathode, the tube won't conduct. Ergo, no current = no damage. But I assume the OP did test the amp after the repair and found this to be true.

Catnine, are there other problems your experiencing now?

[catnine]

I changed the bypass caps and 1.5k cathode resisters to be safe . Then I added the diodes some said were to protect the PT HT secondaries is the rect tube shorts out . Before I added the diodes I read 330 VAC on each secondary lead after the diodes were added now I read 175VAC and also DC is this ok , is it because the diodes rect AC to DC . I don't know if I like this yet the plate and all other voltage readings didn't change.

[Chuck H]

Well, what's not to like? It shouldn't sound any different. I've never done this myself, but I expect your lower VAC reading is because you can only measure 1/2 the AC cycle with the diodes on there. Measure behind the diodes and your AC should read normal. The rectifier tube is just a pair of diodes too. So it doesn't care if it's passing half an AC cycle or DC.

[catnine]

+1

If you lift the cathode, the tube won't conduct. Ergo, no current = no damage. But I assume the OP did test the amp after the repair and found this to be true.

Catnine, are there other problems your experiencing now?

No , the problem with the crackle with the vol pot rotated is gone now . I was told somewhere and I can't recall what forum it was perhaps the fender forum that the bypass cap might have gotten over voltage so I decided since I have four sprague 25uf 50 volt caps to just replace the caps and resisters on both V1 and V2 .

As far as the diodes in series with the rect tube for protection all I had were 3 amp diodes and they were to large so I just tack soldered them in place to see the outcome . What I don't like is that even with 1 amp diodes which are much smaller the rect tube socket is so close to all the PT center tap grounds and the line fuse holder I wouldn't be able to get heat shrink to cover the diodes and connections to shrink , can't use heat right there so I would need to pull everything out of the way to do this proper. It was difficult enough to get the soldering iron in there and not melt some lead just to un-solder the PT HT leads off the rect socket . I put the PT in first and all the tube sockets and then wired up the heaters then before the PT leads were soldered to anything I installed the rect socket first . I had to plan it all out so I could build this amp is the small chassis I have it in. The chassis is the exact same size as a SF champ and is as I said it' a 71 Fender music master bass amp chassis same thing different holes than a SF champ . Fender built their smallest push /pull 6V6 amp in a larger chassis , deeper . longer and wider . My build is like stuffing a 5E3 in a SF champ Chassis.