Need troubleshooting help w/ '63 Ampeg R12 Rocket...

[beinhard]

Hi, 63Polara

Do you have the correct schematic for your amp? The ones I found for the J12b don't look quite right.

To me it sounds like your problem is in the oscillator circuit, and a resistor that has drifted way off from its value could cause this.
I would also check the speed pot for poor contact.

beinhard

 

[63Polara]

Hello, yes I have a copy of the schematic. I have replaced all the caps in the trem circuit as well as trying swapping the tubes. Can just this bad resistor cause the trem to fade off after just a couple seconds?
Thanks

 

[63Polara]

I have also checked both the speed and intensity pots and they are both fine too.

 

[beinhard]

Can just this bad resistor cause the trem to fade off after just a couple seconds?

It would be easier to answer that if I had seen the schematic and knew exactly which resistor you have measured.

A component this far out of spec is likely to be a problem, but not necessarily the only problem.

beinhard

 

[63Polara]

I will get a copy of the schematic posted.
Thanks for your help.

 

[63Polara]

Here is the schematic for my R12. The resistor that read bad is the 270K on at the top of the trem circuit, between the "A" and the tube.
Everything else in the circuit has either been replaced, or tested to be good.

Thanks again for any help!

 

[beinhard]

I believe you may have found the problem.
A resistor with far too high value in that location will reduce the output of the oscillator or stop it completely.

beinhard

 

[Default]

Now you can understand the value of having a meter. Having a 1.5 meg resistor in the power supply certainly dropped the voltage for the oscillator circuit far below the necessary amount.

 

[63Polara]

Sounds great, hopefully I will have a new resistor over the next few days and I will report back with the results.
Thanks again!

 

[63Polara]

My tremolo works! It was the resistor. Sounds and works great now!
Thanks for all the help!

 

[Default]

 

[bluesypicky]

My boy....
I usually have no idea what he's talking about, but threads like this one make me believe he has an idea himself...he good ain't he? 8)