Miller Audio

Miller Audio LLC

Module AB-Qi for 4 tubes, PP & PPP amps, with a 1:1 isolation transformer for use in amps


The model AB-Qi auto bias module is designed to optimize the bias for four 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-Qi dynamically controls the bias in four 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 has a 1:1 12V isolation transformer for the 6.3VAC supply, making it suitable to use in an amp where the 6.3VAC filament supply is referenced to ground!
– PCB dimensions are 125mm x 50mm x 15mm high / 5″ x 2″ x 0.6″ high
– isolated 6.3VAC for use with ground referenced 6.3VAC filament supply
– negative DC bias supply between -50V to -250V
Price for one AB-Qi module: US$80.00       in stock
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.


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