Fender Dual Showman Reverb Problem

[MWJB]

"Should I use the balance pot to set the bias? Is that its function?" Er...yes. It should help some.

You also need to change the resistor grounded from the bias balance pot, go larger until all your tubes read 30-35mA.

[RiccardoSG]

To resolve the problem I want to convert the bias balance pot in a bias pot. I found this web site but I don't know if is good or bad.

http://www.el34world.com/charts/bias_conversions.htm

Do you have some enteresting link?

[MWJB]

That's how anyone would convert a bias balance to bias adjust, follow the exmples for AA270 Twin Reverb. You will need to use a matched quad of tubes to ensure they all draw the same current +/-5mA.

If you replace the resistor grounded from the bias pot with a cermet trim pot, you willl still have bias balance and the trim pot will be bias adjust. Set negative voltage at pin 5 to -55vdc without the tubes in the amp, then install the tubes and fine tune current.

[RiccardoSG]

In my amp I have a wire that come from the vibrato section and come to the lug that has a cap grounded in the bias balance pot. Do yow know where do I must solder it? I think I must solder it at the lug down on the right side but I'm not shure.

I want to replece al the power supply filter cap and the bias filter cap, should I re-form the bias cap too?