Help my amp now has tremolo....

[Steel Duck]

Hi all.
I have a 3E5 amp built from a Ceriatone kit with MM transformers, and it worked great untill my stupid bandmate dropped it on a concrete floor. Now the first channel doesn´t work at all.. no sound. The other channel wors but without the interaction of channel one. But, when i turn up channel one all the way i would still get that changed tone with less gain that i used to, but here is where it gets really weird (to me at least): at some point i pulled a 6v6 tube, and with the unused (and unusable) channel turned all the way i now got a really wild tremolo!!! The one 6v6 tube still in flashed blue in time with the tremolo. When i changed the output tube to the one i first pulled that all stopped. I tried measuring for continuence from input and all the way through channel 1´s signal path and could not find anything wrong. Does anybody have any idea why this is happening?? Channel 2 still sounds good by the way


Edit: even if you have no way of knowing what is wrong here any information on what could cause these things would be appreciated. I´m just trying to learn

[MWJB]

Run both power tubes all the time! If your 5E3 is typical it runs the 6V6s on the hot side, running one tube only effectively halves the value of the cathode resistor for that tube, causing it too draw way too much current & possibly die.

"The other channel wors but without the interaction of channel one. But, when i turn up channel one all the way i would still get that changed tone with less gain that i used to," Sorry, you've lost me. Channel 2 works but with no interaction, but when you adjust volume 1 the sound of channel 2 changes...that sounds like interaction to me?

If you plug a cable into channel 1 and dab the end with your finger do you get sound out of the speaker? If not, the signal path is interrupted somewhere. Use your DMM (set to dc volts) to probe the wiper of the #1 volume pot, then the plate of the #1 channel input plate at V1 (do this at the end of the 100K plate resistor on the board - be prepared for a very LOUD pop, best keep the volume down doing this). If you get disurbance noise at the vol pot & the plate, but nothing from the amp's input (where the cable is), then the break is between the input jack and V1 grid (pin 2 or 7 depending on channel).

It would be handy if you could call the channels by name ("Mic/Normal" nearest the end of the chassis & "Inst/Bright" next to the vol control) as you have four inputs, 2 of each are numbered "1" & "2"...which gets confusing. I am assuming that neither input "1" or "2" work on the broken channel?

[Steel Duck]

Oh yeah sorry. Its the mic channel that is not working. It is true that there is interaction, but i should be able to get sound just by turning up the unused channel and that is the interaction that i have lost. None of the mic channels inputs work and there is no sound no matter what if i plug into it. I shall remember not to pull any tubes again. In fact i don´t really know why i did it, but do you have any idea how that would make a trem effekt??

[MWJB]

"but i should be able to get sound just by turning up the unused channel and that is the interaction that i have lost." Er, not if there is nothing plugged into that channel, or that channel doesn't work. It's not normal (but it is possible) to get some crosstalk, but it's not a normal feature of a tweed Fender.

"I shall remember not to pull any tubes again. In fact i don´t really know why i did it, but do you have any idea how that would make a trem effekt??" bad layout, bad grounds, loose pots, fault in the circuit...what you have is motorboating/instability - it may, or may not be related to your broken channel, fix the channel first. If your wire to pin 2 of V1 was broken between the input resistors and the tube pin, you would have no load at the grid, tube goes into runaway and destroys itself, possibly causing motorboating/odd noises.

[Steel Duck]

Ok, thanks. I will get some time to work on it tonight or tomorrow. Then i´ll report back wit results.

[Bruce / Mission Amps]

"but i should be able to get sound just by turning up the unused channel and that is the interaction that i have lost." Er, not if there is nothing plugged into that channel, or that channel doesn't work. It's not normal (but it is possible) to get some crosstalk, but it's not a normal feature of a tweed Fender.

......

Actually, with respect to a tweed Fender that has two volume controls, a single tone control, a first preamp stage which has both triodes with the shared cathode resistor and capacitor, (breathe) ...
when plugged into either channel and not the other, the unused channel's volume control is still active and the triode will amplify audio and I think it is because the shared cathode causes the unused channel's triode to be cathode driven, creating very solid signal to the unused channel's volume pot.
I think the only way the unused channel does not create usable audio is if the unsed channel's triode is now bad, the grid not grounded or it's cathode is no longer connected to the common biasing resistor.
As a matter of fact, if you split the cathodes on these amps (using separate resistors and capacitors for fine tuning), the "effect" is defeated.
This is a clue to me sometimes when I'm helping some builders after they tell me one or the other channel is not working.... many times they have an open cathode or a bad solder joint on the socket itself.

****************
This was all assuming that the input jacks and volume controls are wired correctly, of course.

[MWJB]

I stand corrected.

[Steel Duck]

Hi, it was the cathode that had lost its connection. Thanks a lot for your help! Now it works great. I just need to tame the gain a bit. I´ll start with some different tubes just to see how that works.