Bias Mods for Fixed Bias Amps

Allows for the use of unmatched tubes, other tube types (in some amps), and easy tubes changes. Essential for players wanting to be able to use NOS power tubes and experiment with tube types.

Please note these mods are available for any handwired amp and only select PCB board amps.

Description:

Most of the amps on the market today are fixed bias meaning they apply negative voltage to the grid of the power tubes to bias them. Usually a small internal trim pot sets the bias level. When power tubes are changed the amp needs to be biased to the new set of tubes. Unfortunately, the bias systems in the vast majority of amps are minimalist with single bias control for all the power tubes. This is why you have buy matched sets and if you one power tube fails you have replace all of them. NOS tubes often are hard to find matched pairs so many tubes people have or that are for sale cannot be used in their amps. Our bias mods give you a bias control for each tube so you can replace them one by one, use unmatched tubes, and even use mixed pairs. We also install bias monitoring test points so that biasing is simple and safe.

The cost varies from model to model so let use know what you have and we will provide a quote. We only provide this service on hand wired amps and 70’s and 80’s Marshalls that have lots of extra room inside.