Vibrato on Silverface Fender Bandmaster Reverb

[corliss1]

Hey Crew,

Hoping someone has some thoughts on this. I've got a 69 Fender Bandmaster Reverb. The vibrato was really weak, did a recap, new trem roach, brought it back to life. However, the vibrato doesn't work on the slowest positions. It has to be set to about 4 to turn on. Below that, the light in the optoisolator stops flashing. If you have it set to 7 it sounds just fine, but if you turn it down to about 2-3 the light slowly dims and the vibrato stops.

Thoughts? Things to check? All the caps in that area are new, voltages look alright, and the resistors are the values they should be.

Thanks for reading this/for giving any insight you may have.

[mort]

I'm a beginner so let someone else confirm or deny, but I would first be looking at the pot and making sure it still passes signal in those lower positions.

[corliss1]

The pot tests good - both on a meter and when running a signal through it. I'm sure that just adds to the confusion!

[corliss1]

Okay - I put the pot back in, and here's a more accurate description.

It works fine speeds 10-4 - when you try and go lower than 4 the optosiolater actually stays lit - it doesn't go off how I previously though. So, it's like it's stuck on the wrong half of the vibrato wave, which explains the loss of volume. Also, you can't re-engage the vibrato without shutting off the footswitch and then readjusting the knob. Make sense?

[g1]

So the oscillator is stalling at low speeds. Have you tried other tremolo tubes? The high value resistors were checked with one leg lifted? Other than that, maybe one of the new caps was no good.

[corliss1]

Oh. My. Goodness.

Once in a while, apparently I need people to remind me of the obvious - that being tubes are in sockets for a reason.

I guess I just never questioned the tube because it worked great at the higher speeds. I put in a new 12at7, bam, vibrato on all speeds. Must have just been a weak tube?

I love the amp - it's got a great sound and a really useable vibrato. Thanks for setting me straight!

[g1]

That's great, but did you mean 12aX7?

[corliss1]

Why yes...yes I did - going to be one of those days apparently...

[timrichter9]

Yes. These TFL5005 Bandmaster Reverbs were the sleepers for a while. Essentially, they were very similar to the '64 Vibroverb that Stevie Ray Vaughan used (with a middle control). The hip thing in the 1990s was to have a 1x15" combo cabinet built for it and it was known as the Vibroclone. I have one and it is pretty great for chimey clean guitar (and breaks up decently also).