Dual independent bias for a Windsor

[JacksonRR]

Hey guys... Been some time...

Well I grabbed a Peavey Windsor for a song and really got to work on the preamp. Sort of a tweaked ENGL design with a clean channel at the moment. Very happy with it. Did not cry Sunday when I sold my 5150....

Anyways, I want to bias the inside and outside pairs separately so I can use 6L6s and EL34s at the same time. I did find a few threads here with some supply ideas/schematics and that's all well and understandable... but I'm not versed on the implementation so... start a thread and ask for help.

I see the bias supply is tied to a voltage divider there at R10/R9.... Certainly it can't be as simple cutting the traces connecting the supplies for V4 and V5, connecting my new supply and tie that to a new voltage divider in parallel with the previously mentioned one...

http://img535.imageshack.us/img535/8...or20schema.jpg

Thanks in advance for any help/suggestions.

[Enzo]

R9,10 is not a voltage divider, just a splitter. Unless the tube grids start to draw current, there will be no voltage drop across those resistors.

The power supply is on page 3, and there is a voltage divider there for bias. R20, VR9, R23 are its parts.

To make separate bias circuits, you will need to separate the power tube circuits. You will have to isolate R9,10 and C7,16 from two of the tubes. In other words the grid stoppers can stay, but you will need to duplicate those four components. There will now be two caps coming from the plate of the phase inverter and two from the texture board. On a circuit board like this, this can be more complex than it might seem. Ther are some wire jumpers on the board in the grid circuits that should HELP make it easier, but be VERY cautious, and doublecheck everything. And don;t overlook those 10k suppressor grid resistors tied to bias.

The original R9,10 are already wired to the bias supply. The new pair will need their own run to the bias supply. I see no open wires in the ribbon, so you will have to run a wire.

On the bias supply itself, you will want to duplicate everything from D3 to R23. COnnect your new D3 to C30 like the old one.

[JacksonRR]

Thanks! That was a great answer and all I needed.
Will try to get this done on this on Sunday.