1967 Twin Reverb 2

[karl]

My reverb isn't working. I swapped cans with a London Reverb and it still doesn't work. The cables are correctly installed and the output works as it makes the typical reverb banging noise when the can is disturbed. How do I kinow if it's tubes or transformer? Which tube should I check first? Just a novice at this repair business but I love this old amp. I am the 2nd owner and have used it professionally since the early 70's.
Thanks/Karl

[Chuck H]

The first thing to try is replacing the reverb driver tube. I can't find much info but it looks to be the third tube, counting from the first preamp tube. And it should be a 12AT7.

BTW, I think your memory may be skewed somehow. The Twin Reverb II didn't come out until 1982! It can't be from 1967. In 1967 the Twin Reverb was still the original BF type model. So it's very unlikely that you've been using that amp since the early 70's unless you also own a time machine.

[Tom Phillips]

Well there is some confusion here about your amp model. (Twin Reverb 2 vs 1967 Twin Reverb) Let’s assume that it is a 1967 BF Twin Reverb.

I don’t believe that the London Reverb Tank model will work in a 1967 Twin Reverb . Therefore , I’m assuming that the tank swap that you already did was not a definitive test. Following is a test that I suggest you try.

1. Get your amp warmed up and verify that you still hear the crashing sound when you shake the tank. This should be done with your original Twin Reverb tank. This verifies that your reverb return circuit and the tank recovery transducer (assuming the reverb cables are correctly hooked up) are operative. I know you already did this but I want you to start at a known operating point.
2. Now put the amp on standby and without changing anything else, swap the positions of the reverb cables where they are plugged into the rear of the chassis. This is a diagnostic test only so don’t get diverted by thoughts that the tank may be connected backwards.
3. Put the standby switch back in operate position and shake the tank again. Do you still hear the crashing sound?
   If YES then we have verified that the tank driver transducer and associated wiring are OK. It’s now time to trouble shoot the driver circuit in the chassis starting with the tube.
   Note that now is a good time to try the reverb by playing guitar through the amp in case you got something mixed up previously and the cable swap has fixed the problem.
   If NO then we have found that one of the following are bad:
   A) The wiring from the tank RCA jack to the driver transducer . Time to look inside the tank.
   B) The cable from the tank to the chassis is bad.
   C) The driver transducer inside the tank is bad.

Please report back with your results and we will go from there.
Edit: By the way - the above test should also apply to the "Twin Reverb II".

Regards,
Tom

[pdf64]

We need to identify the amp; is there a model number on the tube chart, inside the amp cab?
The London Reverb is a silicon based amp; they tend to have different spec reverb tanks than tube amps, eg much higher impedance drive coil.
Pete.