Model AB-Q-ST70-ST120
The model AB-Q-ST70-ST120 auto bias module is designed to fit the Dynaco ST70 chassis and can be used in an original Dynaco ST-70 upgraded with a VTA driver circuit or the new generation Bob Latino ST-70 and ST-120 stereo power amps.
It comes with a 1:1 isolation transformer so that the module can safely use one of the PA-060 power transformer 6.3VAC filament windings for its power.

The AB-Q-ST70-ST120 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.

If you have an original and unmodified Dynaco ST-70 amp and wish to buy this auto bias module, click here.

- PCB dimensions are 100mm x 57mm / 4" x 2.25"
- Suitable for Cathode Feedback amps
- power supply requirement is 6.3VAC from one of the PA-060 filament windings
- negative DC bias supply between -55V to -90V


Price for one AB-Q-M125 module: US$85.00       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 below PayPal button to purchase, as shipping of US$17.00, instead of US$8.00, will be added to the unit price.