Variable Power Control – VPC1 Kit

Our Variable Power Control is a quick and easy way to install variable output power reduction in your amp. Our VPC Kit easily installs in cathode biased amplifiers that are rated up to 60 watts. There are only 3 connections to make in the amp – B+ in, B+ out, and Ground. The active device is a 900V MOSFET that must be mounted to the chassis by one screw, insulating washer, steel washers, and nut.

VPC allows the user to infinitely vary the B+ voltage, thereby reducing the power output. In this manner one can crank up the amp for great overdriven tones, yet effectively control the output and overall volume.

The board is 1.25″ x 1.25″ with the control pot mounted at the front, so it’s very easy to fit, by either using an existing chassis hole, or drilling a new one. (Downloadable) instructions, mica insulating pad, 600V wire, and a MOSFET mounting kit are included. As of Jan 2022, we are supplying the kit with red PCBs.

Please note: Our VPC1 kit will not work in amplifiers that use a fixed bias supply (negative voltage on power tube grids). For those applications, please see our VariWattage kit.

Beginning in 2018, instructions for modification kits are now online for your convenience. This allows us keep our prices competitive, and helps all of us reduce paper waste. Links to PDF files will be included in the order status email when the order ships, and always available in your order history. Please add to your email whitelist to ensure you receive our emails.

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. Read resistor color codes and capacitor values. Proper isolation and mounting of FET and transistor devices to insure adequate heat dissipation. Measure and connect high and low voltage AC and DC. Understand basic working of vacuum tubes. Use all functions of a multimeter. Understand Ohms law and apply to basic circuits. Work with basic hand and power tools.]

Pricing and Options


3 in stock (can be backordered)

Control Knob(s) *


    Be the first to review “Variable Power Control – VPC1 Kit”

    Your email address will not be published. Required fields are marked *