I had an unusual valve kicking around – an ECH83. It’s a triode-heptode designed for use in car radios, with an anode voltage of only 12.6V.

I also had a couple of the ubiquitous Park G10 practice amps from my early guitar-playing days waiting to be recycled into something better, so I thought I’d see if I could concoct some sort of bastardised hybrid.

The G10 actually has quite a nice chip amp for it’s final stage; the TDA2030A. What a pity about the JRC4558 preamp stages. I really hate the sound of that particular 80’s opamp.

Inspired by this wanton ECH83 abuse by Engels, I decided to use both the triode and heptode in the ECH83 as preamp stages and salvage the silicon from the G10 for a power amp stage.

This is the result (click to enlarge):

Read on for explanation, layout and construction notes.

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