Adjustable Bias Modification Kit

With our Adjustable Bias Modification Kit you can modify your non-adjustable fixed bias amplifier so that you can set the bias for optimal performance, and use other types of power tubes instead of the manufacturer’s “required” type. Great for amps such as older Marshall, Peavey 5150, many Mesa Boogies, and other type of amps.

Our kit includes a small PCB with your choice of 10K, 25K, 50K trim pot, or 25K, 50K full-sized Alpha pot (for external mounting for biasing without removing the chassis), your choice of bias range resistor, 1 ohm, 2 watt, 1% bias measurement resistors (2, 4, 6, 8, or none, see dropdown below to select), mounting hardware, a section of stranded wire, and a guide for installation and bias procedure (via download).

If you need help determining the values to select for your particular amp, please contact us!

Note: Components shown in photo are for reference only. Depending on your selections, components may vary in appearance. Please note, the Alpha pots are not mounted to the PCB.

DISCLAIMER: User assumes all risks. Performing these modifications will most likely void the warranty on your amplifier. Working on amps can be deadly if you do not take proper precautions. Read and follow the diagram or instructions very carefully. Basic soldering skills and basic user-supplied tools are required. If you are at all unsure of your ability to perform these modifications STOP and take your amp to a professional to be modified. You can also send your amp to us for modification. Contact us for pricing.


DIFFICULTY LEVEL: INTERMEDIATE [Follow safety guidelines for working with electricity. Basic soldering skills and knowledge of working with AC/DC circuits. Identify all terminals of electronic components using data sheets or schematics. Read resistor color codes and capacitor values. Measure and connect high and low voltage AC and DC. Understand basic working of vacuum tubes. Use all functions of a multimeter. Understand Ohm’s law and apply to basic circuits. Work with basic hand and power tools.]


Pricing and Options


13 in stock (can be backordered)

Potentiometer *

Resistor *

1 Ohm Bias Resistors *


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