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

link to stripped down file