Copper Panel AC30 Trem/Vib Issue

[ckpop]

Hey everyone I need some advise on replacing the 12AU7 for the Trem circuit on my JMI AC30.
Here is the issue ......... I tried several 12AU7's which all are good but only one of them will make the Trem/Vib work ????? Why would this be ???? Is it maybe pulling the voltage down in the correct range for the circuit to work and the other 12AU7's are not ?????

[Masco]

The 12AU7 is the mixer, did you happen to replace the 12AX7 oscillator tube, which is next to it (going toward the OT/speaker connection side of chassis)??

[HeeBGB]

I had a similar issue with a vintage Sano amp I recently had. I cleaned the tube sockets. For whatever reason I had one tube that worked but no other tube would work. I cleaned and tensioned the tube sockets and it worked fine afterward with all tubes. In this case the tensioning was probably more the case. The one tube that worked probably had a bent pin that allowed it to work. Anyway it may not be your issue but probably worth a try.

[JoeCon]

HeeBGB

Sir, could explain how the tensioning is done? It something I've never done but sure would like to know how...maybe other newbies too!

Thanks....

[HeeBGB]

Ok well the pins go in the tube sockets and are in a sort of clam shell made of metal. The two sides of the clamshell separate over time due to heat and assorted other things. You have to gently bend them back into place so they are snug on the tube pins. But be careful. If you bend them too far it will
Make it difficult to get the tube into the socket or worse you could break it and then have to replace the socket. I use a small flat blade screwdriver and slide it down the outside of the contacts until they are a bit tighter.

As I said earlier i don't know that this is your problem but it was definitely the issue with my Sano

[ckpop]

So here is the strange thing ........ I have two Copper AC30's and I took the 12AU7 from the working Trem AC30 and popped it in non working Tremelo amp and it started working. Any other 12AU7's I placed in either amp the Tremelo does not work in either amp. I tried three different 12AU7's that all test good.

Should it be normal to have to roll 12Au7's in a Vox AC30 to get it going ?

[Masco]

Should it be normal to have to roll 12Au7's in a Vox AC30 to get it going ?

Only if they're bad.

[HeeBGB]

Do all the 12au7's work in the other AC 30? If so tension and clean the sockets as described above. If they do not work in either amp then they are bad even though they test good. One question. What are you using to test them?

[ckpop]

No the other 12AU7's do not work in either AC30. I used a B&K 747 tester and a the Orange valve tester. There is only one 12AU7 that makes the Trem work in both amps. This is the process I will do to try to figure this out.

Re test tubes on the tester

Measure voltages with the 12AU7 that makes the Trem work and then take measurement with other 12AU7's that don't work

Maybe the parts have drifted and for some reason the certain 12AU7 causes the circuit to work ?

I do notice with the 12AU7 that don't work in the circuit when you power down you can hear a hint of tremolo kick in which indicates parts drift or voltage not correct.

Will let other know what I Find