Auto Bias Modules
Erhard Audio is proud to be the exclusive agent and reseller for Audioamp's, based in the Czech Republic, Auto Bias modules for the USA and Canada.

These modules have been designed to maintain a constant bias voltage through all power output tubes of your tube power amp and can be retrofitted in just about ANY tube power amp, mono or stereo, where manual bias adjustment is required.
The bias is kept at a constant level on the output tubes, irrespective of the signal level.

The advantage of using these auto bias modules is that they will extend output tube life, in a lot of cases it will also improve the sound and last but not least, you will never have to worry about adjusting the bias again.

  
-     No need to keep an eye on and/or adjust the bias of the output tubes

-     Significant extension of the output tubes' life

-     Bias remains constant regardless of fluctuations in the input signal dynamic

-     Undistorted and improved sound for a greater listening experience

-     Reduction in hum and noise level of the amp

-     No maintenance or additional adjustments are required after the initial setup

-     Improved overall operation of the amp due to the reduction in the danger of a tube red plating

-     The auto bias modules ensure that bias is kept at the pre-set value even as the tubes age

-     The auto bias modules come with a soft start feature, which slowly brings up the bias to each output tube

-     Installation is straight forward, downloadable and comprehensive manuals

-     These modules are suitable of Push-Pull (PP), Parallel-Push-Pull (PPP) and Single Ended amps

-     These modules will work with two or four tubes

-     These modules will work with class A, AB and B tube amps

-     These modules will work with a wide range of negative bias supplies, from -50V to over -120V

-     An on-board LED indicates when the auto bias is first powered up followed by another set of LED's once the         pre-set bias level has been reached and the amp is ready. These LED's will also indicate if there is an issue
      with a tube and that it needs to be replaced

-     The auto bias modules will operate with a  6V to 12VAC supply, so that can be tapped off the amps 
      filament supply (NO reference to ground!), OR, the auto bias modules are available with their own dedicated
      power supply

IMPORTANT NOTE: If ANY modification is carried out on any auto bias pcb, such as remote LED's etc., this will void any warranty, no exceptions.







Module AB-Q for 4 tubes, PP & PPP amps, requires 6.3VAC & bias supply from the amps circuit. Not suitable where the 6.3VAC filament supply is referenced to ground, use the ABF-Q below.
Or use the small islotation transformer we sell separately, see beow.
Module AB-D for 2 tubes, PP & PPP & Single Ended amps, requires 6.3VAC & bias supply from the amps circuit. Not suitable where the 6.3VAC filament supply is referenced to ground, use the ABF-Q below.

BEST SELLER!
Suitbale for Cathode Feedback PP amps!
Suitable for Single Ended amps!
Module ABF-Q for 4 tubes, PP & PPP amps, with a 1:1 isolation transformer for use in amps where the 6.3VAC filament supply is referenced to ground. Also requires bias supply from the amps circuit.
Module AB-Q-ST70/ST120 This module has been designed to fit the Dynaco ST-70 chassis for the new generation Bob Latino ST-70 and ST120 stereo amps. It comes with a 1:1 isolation transformer to safely use one of the PA-060 power transformer 6.3VAC windings for its power.


Module ABS-Q+ for 4 tubes, PP & PPP amps, with a built in 6.3VAC AND bias supply, 115V or 240VAC powered transformer, fully autonomous.
Module AB-Q-M125 This module has been designed to fit the Bob Latino M125 mono block power amp. It comes with a 1:1 isolation transformer to safely use one of the PA-060 power transformer 6.3VAC windings for its power.
Also suitable for the Dynaco MK3 mono blocks.
Module AB-2 for 2 tubes, PP & Single Ended amps, requires 6.3VAC & bias supply from the amps circuit, with TTL error signal ouptut.
Suitable for Single Ended amps!
Module AB-4 for 4 tubes, PP & PPP amps, requires 6.3VAC & bias supply from the amps circuit, with TTL error signal output.

Back to Erhard Audio
For all inquiries and technical support, click here
1:1 isolation transformer for use with AB modules without their own built in unit to safely use with an amps 6.3VAC filament supply which is referenced to ground. Comes with its own mini pcb for easy wiring.
PRICE: $15.00 including the mini pcb
includes shipping to the lower 48.
For all other areas and overseas, please contact us first, thank you.
We recommend that you use the small 1:1 isolation transformer for the 6.3VAC supply, see below.
We recommend that you use the small 1:1 isolation transformer for the 6.3VAC supply, see below.
We recommend that you use the small 1:1 isolation transformer for the 6.3VAC supply, see below.
BEST SELLER!
Module AB-D-MKIII. This module has been designed to fit the Dynaco MKIII amp chassis!
It is identical to the AB-D module above for two power tubes, only the pcb shape has been changed to fit the MKIII chassis.
This module does not come with an isolation transformer and therefor a separate isolation transformer needs to be used, as the Dynaco MKIII has the 6.3VAC winding referenced to ground!
This isloation transformer is available below.
We recommend that you use the small 1:1 isolation transformer for the 6.3VAC supply, see below.