Posted by Thermionic [ 70.173.99.212 ] on January 27, 2006 at 13:25:13:
In Reply to: Fender Bandmaster Vibrato Problem posted by Mike D on January 27, 2006 at 07:45:15:
Hi Mike,
The glow you see down the input jack is not a valve, it's the optical device that allows the vibrato to work. Earlier Fenders had all-tube tremolo/vibrato, with a tuned positive feeedback circuit that caused the oscillation. Yours has the later "optoisolator" tremolo/vibrato, which uses a cadmium sulfide photocell and a light source. The fact that you can see the pulsing light through the jack hole is not good. There is supposed to be a sleeve that fits over the photocell and light bulb.
Another cause may be "CBS Syndrome." By the time your amp was made, all sorts of quality control issues were going on, courtesy of the corporate bean counters at CBS. There were MANY amplifiers that left the factory with non-functioning vibrato. Some would cut out intermittently, and it was later discovered that several connections weren't even soldered! If the vibrato has never worked, I'd guess something is wired incorrectly or isn't wired at all.
The things I personally have seen in early post-CBS era Fenders would blow your mind. Thankfully, your '65 is the AA763 circuit, made before CBS started "tweaking" on Leo Fender's original design.
The filter caps in your amp drain pretty quickly, as they have bleeder resistors. Plus, at their age, they generally leak down pretty quick. Do beware the filter cap on the bias supply, as it will stay charged up much longer than the main power rail's caps, although it packs much less of a punch. You should consider having your amplifier recapped and the rectifiers diodes replaced, which will not only improve the sound greatly but increase it's reliability 100%. It's not IF but WHEN one of those old filter caps will blow!
If you don't see something readily obvious when you pull the chassis, you'll probably (sadly) have to be without your baby for awhile, and send the chassis to a competent tech.
Thermionic 
[ GuitarAmp Forum ] [ Help ]