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

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

The AB-D dynamically controls the bias in two 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 12.6V AC.
It is important to note that the AB-D will not operate if the filament supply has any reference to ground, such as a center tap.
For that scenario, use the auto bias module models ABF-Q or ABS-Q+ or provide your own small power transformer of around 2VA with, for example, a 9V secondary.

- PCB dimensions are 65mm x 57mm / 2.55" x 2.25"
- Suitable for single ended amps
- power supply requirement is 6.3 to 12VAC
- negative DC bias supply between -70V to -120V

Price for one AB-D module: US$62.00      in stock
Shipping of $8.00 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-D options: