The Amp Garage

I am trying to implement quad bias controls on my 100 watt heads. Is this the right approach to do this. I would like to simulclass by mixing tube types as well. KT88, EL34, or 6L6. This is my working schematic. Will this work like this?

Here is the completed amp. It sounds great and it sings nicely. My heaters are running about 6.9VAC. I left accomodations for dropping resistors. Should I drop it down of just leave it? I suppose I will leave it because it is at the +10% tolerance. The plates are running @ 520VAC. Love the tone. Sta...

Had to be sure of the bias circuit before overhaul! I had planned on re-build anyway. The amp is gonna be a single channel with hi gain circuit. It is getting new caps, sockets, and new pots. I won't deny the bias circuit was a PITA! I will post pics when complete.

Well I will be utilizing the voltage doubler with separate bias controls for each tube. Pic 2 is the prototype bias circuit and pic 1 is the stripped version prior to rebuild. Should be a nice amp whem complete. I will be adding a presence control to it as well.

Found the Vishay substitute. Thank you for the help! Appreciate it!

Does anyone know where I can find a source for these capacitors? Thanks

I have decided to keep stock transformer on 105VAC tap as it is and run a voltage diubler for the bias circuit. I will be dropping heater voltage a little bit to keep it with in tolerances. Thank you for all the great info on these amps!

I got this schem from another forum. Looks like a workable option. Voltage doubler.

Those readings were based on resistor changes. With the original schem 4.7K in place it is adjustable from -44 tp -42 or so. I will probably be tapping the HV and totally re-work the bias circuit.

Appreciate the info. You are correct! I need to increase bias voltage to decrease bias current. Yes my 2 options are: Take it from HV tap or rectify the bias tap with full wave rectifier. Where could I find an example of these applications? Ex: schematics. Thank you for the help!

These are close, but no brown availiable- only 5 wires as stated
2 large - black and yellow
3 small - green, red, white


Power Tranny
Primary Windings
Grey- Tranny Shield
Black- Common
Orange- 105v
Brown- 115v
Yellow- 225v
Red- 245v


Partridge Mains transformer
TG9875
H2138H

Well I would like to return to the original source of the problem here. Does anyone know where I can find original color codes of these 50 watt partridge output transformers. I know there are 5 wires leading to the input circuit. Large black and yellow - Small Green, White, and Yellow. Any info on t...

I either check it with a weber bias rite meter or a fluke meter. I do not have the 1 ohm resistors on this amp. There are individual adjusters on each tube. It shouldn't matter as long as I bias each tube separately

The bias caps?

Played with value of R43 went from 470R to 499K. The bias will not go below 74 to 80ma. The bias tap off the transformer is 33VAC. The readings @ pin 5 with no tubes installed is between .500 and -44 VDC. These voltages are obtainable by rotating bias adjusters. The schem shows a voltage of -36, but...