Princeton Reverb tremolo broken, everything else works great

[dchang0]

Hi all--

Some time ago, I was moving around my amp in storage and accidentally knocked it over. I turned it on to test it out. Something inside the tremolo tube (12AX7, fourth from the back right) had broken, and even though I replaced the tube with a known good one, the tremolo has not worked since. Everything else sounds as great as it did before the accident, and the intensity knob adds a teeny bit of gain when turned all the way up, so it seems that part of the tremolo circuit is working.

The amp was hand-assembled by me from a complete Ted Weber 6A14 kit, a perfect copy of the AA1164 Blackface Princeton Reverb. It worked perfectly, with deep, lush tremolo, for all the time I had it until I knocked the amp over.

Here's what I've done:

1) swapped in more known-good tubes and tested the footswitch and shorted out the tremolo's RCA jack for good measure
2) done the chopstick-tap on connections to see if any solder joints came loose
3) played with the bias pot to see if that might be at fault, then set it back to where it was
4) measured voltages around the amp and around the trem tube and compared it to the original voltages on the Fender AA1164 circuit diagram. Everything's a bit low, but the voltages coming off the power transformer are 340VAC instead of 400VAC, so that's to be expected.

Any tips? What should I be looking at?

Thanks in advance!

[Gibsonman63]

A couple of quick things.

I believe that you have to have a footswitch (or short the jack) to turn on the tremelo. Have you done this?

Does this vibrato circuit use an opticoupler? If so, pull the chassis and check it in the dark to see if the led (or bulb) is flashing.

[acorkos]

when the tremolo tube took the hit, it may have bent the socket elements. your new tube may not be making contact with all the pin elements. try tightening them.

[dchang0]

@Gibsonman63: Ah yes, forgot to mention that I tested the footswitch and that it does work. I also tried shorting out the RCA jack on the back of the chassis. Neither helped.

And no, it doesn't have an opticoupler. Would be nice if it did, huh?

[dchang0]

DING DING DING--AND THE PRIZE GOES TO acorkos!

While I was tightening the tremolo tube socket's pins, I found that socket pin 3 has part of a broken-off tube pin stuck in it. That pin prevents the new tube from being fully inserted, which is causing the problem.

So if I can't remove the stuck pin, I can replace the entire socket and fix the amp.

Thanks, acorkos!