The model AB-Di MKIV 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.

The pcb has been designed tro suit the Dynaco MKIV mono block

The AB-Di MKIV 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.

and comes with its own built in isolation transformer where the 6.3VAC filament supply is referenced to ground.

– 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 -50V to -250V

Price for one AB-Di MKIV module: US$70.00     on order

Shipping of $11.00 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.