Adjustable bias from 110 or 12V secondary

[Jerry garrcia]

Hi again. Asked a question a couple of weeks ago regarding a PSU for a Princeton Reverb build with a 110V secondary. Got great help and have constructed a Cockcroft-Walton multiplier circuit with three stages. Using 100uF/450V caps and the B+ should land at around 430-460V after the tripler. Uncertain of the ripple but hoping the CRC filter with 100uF and 3x22uF will take care of that🫣.

Now a question about the bias circuit. The aa1164 schematic calls for a -34V bias. First I was thing Rob Robinettes version of the JCM900 adjustable bias supply but realized that since the 110VAC secondary will probably be wrong due it’s created for a much higher HV secondary.
I’m really bad with bias circuits and voltage dividers. Only used cathode biased circuits before.
So what I have to work with regarding secondary windings and the aim is around-34VDC.
110 VAC (710mA)
6.7 VAC (4A)
12-14VAC (200mA, unused).
As usual my chassis space is cramped and it’s a give away amp for a friend of my son since he’s a dedicated jazz guitar player and is using a Spark amp.
I’ll including the schematic of the amp I’m building (with a different power supply), the JCM900 circuit and its bias circuit, a layout of a modified version of that circuit and the PT.
Any help with designing or nudging me in the right direction is very much appreciated. As small as possible. I already built the layout provided before I realized that my input voltage was to low.

[AmberB]

Check out how Bogan derives their negative bias voltage on this CHB-35A.  They also use a voltage doubler for their B+ voltage.

[Jerry garrcia]

Check out how Bogan derives their negative bias voltage on this CHB-35A.  They also use a voltage doubler for their B+ voltage.

Many thanks. Now you just destroyed another night of sleep. An interesting amp abut unfortunately the bias supply is fed from a 170V winding and producing  -24V bias. I’m running it from a 110V and aiming for -34V bias. Also want to make it adjustable since the plate voltage will be different and a bit uncertain on what I will land on.
I might search further with the guidance of the CHB-35A. If anyone has additional inputs they are most welcome. Especially if I can tweak/change values of the previous attached layout since it’s already built and I have a slot in the amp that it fits perfectly. Shouldn’t it just be to change two or three resistors? Those Voltage dividers/calculations gives me an headache. Also regarding the voltage ratings on the cap values in the CW voltage multiplier. Since they are in series I shouldn’t really have to up the voltage ratings on the last two caps? Have 450V ones but they are huge in this tiny chassis…