CMI SG-100 6550 bias conversion

[MstrB]

Hello, I have seen some discussion of this but was hoping for a schematic. I am wanting to change this amp to 6550 from 8417 and would like to see some ideas about how to work the bias circuit. The existing supply gives a range around 35v and I figure I should have double that. The schematic is in the Jack Darr 4th edition.

[Enzo]

Your bias supply comes from a 25VAC winding, so the most you can get from that is 35v unless you use a voltage multiplier. A voltage doubler would net you 70v, more than enough. You won;t get the power from the 6550s like the 8417s. I don;t think I have ever seen a bad 8417, they seem to last forever.

And though it seems clutsy to me, you could also wire in a separate small transformer for the bias supply. Current demand is almost nonexistent.

[MstrB]

I have been looking at voltage doublers but am having a hard time devining which design best works. Most of the circuits show the doubler with its own transformer taps and this one will have to share with the rest of the low voltage supply. can I tap directly off the transformer 25vac without adversly effecting the rest?

[Jazz P Bass]

The voltage mutiplier will be isolated from the transformer secondary windings.
So any circuits requiring the raw 25Vac will be unaffected as the bias current is very low.
Link: Volt Multplier: Voltage multipliers : DIODES AND RECTIFIERS