BIAS MOD – Adjustable Fixed Bias
Changing the stock fixed bias found in many amplifiers to an adjustable fixed bias has several benefits. The first being the ability to fine tune and dial in the correct bias without having to compromise to the nearest resister value or meter through hundreds of resistors looking for the exact value. It also allows the amplifier to use tubes that are not sold by the manufacture as drop-in replacements saving money on tubes. In many cases, you will still need to use the same model type (due to the power transformer’s amperage draw limitations and circuit design), however, the brand of tube can be any brand you desire, as long as the tubes are matched to each other and free of defects.
Desert Amplifier Repair’s adjustable fixed bias modification uses military-grade or high end audio locking potentiometers, ensuring precision fine-tuning and stable bias with no worry of drift during travel or vibrations. 9 out of 10 adjustable bias modifications are 100% reversible without the need to drill holes or permanently modify the amplifier in any negative way. Some Clients prefer to have a hole drilled in a location where its easy to access the adjustable potentiometer from the outside of the chassis.
Note: That type of modification will require a hole be drilled in the chassis that can not be reversed.
DAR will never destructively modify without getting permission ahead of time.
The image above is a Peavey 5150 adjustable fixed bias modification. This modification is 100% reversible.