I've always wanted to try modifying one of these, but this was my first opportunity. I went with a set of 6L6GC power tubes for a little more low end, which required adding a voltage doubler circuit to the bias supply. I also modified the preamp, most notably by removing one gain stage from the high gain channel (making compensations elsewhere), and altering the preamp power supply. Finally, I installed an output transformer from Magnetics Components and threw a "resonance" control on the back panel.
