Model AB-Oi
The model AB-Oi auto bias module is designed to optimize the bias for eight triode or pentode output tubes in Push-Push (PP) or Parallel-Push-Pull (PPP) amplifiers that have their own negative bias supply circuit.

Suitable for class A, AB, or B tube amplifiers.

The AB-Oi dynamically controls the bias in eight tubes.

The module automatically optimizes the bias settings and maintains a strict symmetry of currents through both tube branches in the output stage. It will also stop any DC current flowing through the output transformers, all with the minimum of current loading on the anode of a tube. 
DC current saturates an output transformer which results in increased low frequency distortions.

The bias level is kept at the preset value irrespective of the input signal.

This module may be powered by the filament supply of an amp, with a range from 6.3V to 12.6VAC

- PCB dimensions are 100mm x 100mm / 4" x 4""
- Suitable for Cathode Feedback amps
- power supply requirement is 6.3 to 12VAC
- negative DC bias supply between -70V to -120V


Price for one AB-Oi module: US$80.00       in stock
Shipping of $9.50 for the lower 48 will be added when you click on the PayPal button.
For shipping outside the lower 48, please contact us first, thank you.
NOTE: Hardware such as spacers and screws to mount the module is NOT included.

For Canadian customers, please use the '+ for Canada' option in the 'Add to Cart' menu for additional shipping cost, thank you.
AB-Oi options: