Does anyone know how to slow down the trem on a Vibrasonic?

[Neil Harms]

The speed knob (yeah, I thought of turning down the knob first!) is set at the slowest speed but it's still too fast for me. This is the 95/95 Vibrasonic Custom Fender. Just wondering if there is a simple way to change the range of the speed knob. Anyone know how to do this? What would be really great would be to be able to change to bias vary as on the old brownface tremolux head I had. It sounded perfect but was way light on power for steel. Anyone ever changed a twin style amp to bias vary? Any thoughts on the speed issue? Any comments, much appreciated. Thanks!

[J Fletcher]

You can change the oscillator speed by changing the value of the three capacitors that couple the signal from the plate back to the grid of the oscillator tube. Relying on my memory here, but there are one .01uf, and two .02uf caps that do this. Sorry I can't be more specific, but I think if you bump up the values, the time constant is increased, and the speed slows down. I would suppose you could also increase the value of the speed control, though it would be more difficult finding the right value with the right taper. I'm sure others will chime in with more specifics.
You can mod the amp for the output tube bias modulation type of trem, just follow the schematic for the brown Vibroverb for example. The oscillator is much the same,the rest of the trem circuit is different though...Jerry