need more (negative) bias voltage

[martin manning]

No, do like this:

[Leo_Gnardo]

No, do like this:

Did the voltage doubler on a 200W Hiwatt monster, it works! Used 100V 100uF x2. That one had a trimpot on each output tube, so the only thing left to figure out was what value resistor to use for optimum bias voltage availability. Once I did that, smooth runnings.

[eddie25]

No, do like this:

Thanks for the drawing. I wired this (with 22uF cause that's what I had) into a 15k then another 22uF and pot divider and I'm getting the perfect range.

[martin manning]

Great! Since you have a second stage of filtering I think 22uF will be fine for the doubler caps.

[samrock55]

Here is great way to build a negative bias supply using minimal parts that is safe stable and can be made fully adjustable and its one up design from Marshalls with having no bias windings available picking off of hv windings make the cap. 05 is class x even if cap fails bias will save your tubes! This is especially a great design for using iron with full bridge rectifiers. Thanks Rob Robinette wherever you are!