"An interesting one this. Originally this was a Carlsbro 60 PA head and it was brought to me with a burnt-out power transformer. However the customer wanted to use this on bass guitar, so it needed the input circuits modifying for this purpose. Also he asked if more power could be made available.
I happened to have a power transformer that would do the job fine, so on it went. Utilizing the extra two tube base holes in the chassis (already cut for 4 tubes anyway as in the 100watt PA version), I converted this amplifier to use 4 x 6146 output tubes (the plate-to-plate load for 2 x EL34's (originally) is fine for 4 x 6146's). I built a specially designed stabilized screen grid supply of 220 volts for the 6146's and separate grid one's drive board plus individual bias pots.
At the end this baby was doing 120 watts, no problem, and even though the output transformer was only a 60 watt device; on test this amplifier is still doing 100 watts down to 40cls! Can't be bad at that. The customer tells me he continually uses it for bass guitar on a 2 x 12" plus a single 15" cabinets and it sounds fab! Can't be bad!"