Who knows something about footswitches?

[Ric-O-Buc]

Then you would check the connection at the TRS jack first.

[analogpackrat]

Looking here I see that the sleeve is gnd and the tip and ring are the trem and reverb, respectively. So to determine whether the problem is in the switch or the switch cable/plug or in the amp is simple. Just unplug the switch and plug in a regular guitar cable with nothing connected to the other end. Doing this will short the sleeve and ring which turns the reverb off.

Now with the amp turned off short the tip to the sleeve at the other end of the cord you've plugged into the switch jack (use an alligator clip or anything that is bare metal that you don't have to touch to keep the short in place). This will turn on the tremolo. There shouldn't be more than a few volts on the tip if the amp is functioning properly, but better safe than sorry. Now turn the amp on and play something with the intensity up. If you hear tremolo, the problem is in the switch/cord/plug. If not the problem is in the amp (try swapping out a new 12AX7 for V5).

If it's the switch unit you can also check for a loose wire at the trem switch. It should be apparent how to open up the switch box.

[JakeK]

I'm taking the footswitch to IVG this Friday to see if it works with the other blackface Fender amps they have (Twin Reverb, Princeton Reverb, Deluxe Reverb). If it does not, I'll just order a new footswitch. Stay tuned.

[JakeK]

Guess what? There's something wrong with the amp. The footswitch worked fine with other amps in the shop, but not with mine at home. So what's the problem and what do I do?

This means I'll be ampless for a little while...

[analogpackrat]

Before you take the amp in on warranty repair, tell us what tube you have in V5 (this is the tube that makes the tremolo oscillator). It should be a 12AX7. But if it happens to be a JJ brand you may have found the problem. Some (many?) JJ 12AX7 tubes do not work well or at all in the Fender oscillator circuit. This is a good place to put your cheap junk 12AX7 tubes (Chinese made stuff, for instance). The guitar signal doesn't pass through this tube--it just makes the trem oscillator that drives the neon lamp in the "bug."

If V5 is not a JJ tube, it still may be bad. Try swapping V1 into V5 (V1 is only used in the "normal" channel so leaving it out will not negatively affect the "vibrato" channel).

[paologregorio]

Yep; I had a tube go bad in the trem circuit of one of my Twins about three years back. I replaced it and presto, problem solved.

[JakeK]

It was a tube. They swapped it out...all is good.