3 Relay Switching Board

The 3 Relay Switching Board (version 2) is a versatile add-on board that has three DPDT 5V relays and a regulated power supply all on one board. It can be powered from either a 5VAC rectifier tap/low voltage tap, or 6.3VAC filament tap (as long as the switching ground is floating and not referenced to the same ground as the filament center tap, or the filament supply center tap is not connected directly to ground). We’ve found that doing this, and referencing the board ground (marked ‘G’) to chassis ground, provides for an extremely quiet installation, even in high gain applications.

It was originally designed by Ampdoc for use in the Overdrive Special styled amps, but can be used to switch any functions via 1, 2, or 3 button footswitches as needed (footswitches not included). The board also has terminals to accommodate chassis-mounted LEDs, and can also be carefully cut/snapped into sections to fit almost any chassis – just connect jumpers from the B+ (DC supply voltage, NOT plate high voltage!) and Ground terminals to each section. Wire is not included, and should be provided by user based on application.

Example wiring diagrams can also be downloaded using the links below. Note: All files provided as a courtesy only. Granger Amplification is not affiliated with any company referenced in these files. Any questions related to these diagrams should be directed towards the respective company, and/or support forums.




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: ADVANCED [Follow safety guidelines for working with electricity. Advanced 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, as well as identify PNP, NPN, JFET, MOSFET semiconductor devices. Understand relay and switching logic. Measure and connect high and low voltage AC and DC. Understand advanced working of vacuum tubes. Use all functions of a multimeter. Understand Ohms law and apply to basic and advanced circuits. Work with advanced hand and power tools.]

Pricing and Options


18 in stock (can be backordered)


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