High Voltage HT Dropper circuit

Description

In my work at Keld Ampworks, I’ve found that some amps use voltages that are just too high for the valves. Sure, they work, but any set of valves you put in risks having a very short lifespan.
Common examples are old Marshalls with 550V screen grids on the EL34s and oh so many EL84 amps with a tortuous 400V anode and screen voltage.

Designed in house, this is a little module that I developed for fixing that problem.

To lower screen grids in a Marshall, connect the positive terminal to the screen grid filter cap and the negaive to the screen grid resistors.

To lower anode voltages on an EL84 amp with a centre tapped power supply, connect the negative terminal to the power transformer centre tap and the positive terminal to the circuit ground.

Price is for an assembled module, packs of ten bare PCBs are available upon request.

DO NOT ATTEMPT THIS MODIFICATION UNLESS YOU’RE QUALIFIED TO DO SO.