During the planning of a scratch built tube amp, I came across a 1960’s 16w Japanese mono hi fi amp for $100 on Trade Me. With 3 X 12AX7’s in the front end, a push-pull output stage with 2 X EL84’s and a 6CA4 rectifier tube, it had all the ingredients for a low cost, easy, re-purposing project.
I retained everything from the old school cathodyne phase inverter to output stage, and configured the two dual triodes in the preamp in a Mesa/Soldano style cascade with a three band tone stack at the end of the chain.
I configured the first tube as a pair of common cathode preamps; one half for low gain followed by a switchable gain “crunch” stage using the other half of the tube. The gain control site between the two stages. The other tube acts as a further gain stage and a cathode follower buffer for the tone stack.
Because of the point to point wiring, “tuning” the cathode bypass frequencies, gain and filters by a bit of trial and error to get the tone I wanted was easy. I also placed a switchable filter in the feedback loop from the output transformer to PI as a sort of presence control. I called this one “edge”.
While not a high gain monster or particularly loud, the little amp makes a good fist of everything from super clean to dirty rock crunch with quite a bit of sustain when wound up. It still has the original NOS EL84’s and rectifier, so has been a bargain to build- less than $250 including new preamp tubes.
To complement the amp, I knocked up the appropriate era-correct looking 2 X 10” cabinet with a pair of 20W Jensens.
Pays to trawl the swap meets, garage sales etc.. who knows what may be hiding out there!
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