This 120W Sound CIty PA amp had been converted into a 100W Marshall Plexi circuit by another tech.
These amps are great platforms for Hiwatt conversions and the owner wanted an early 1970's DR103, so that's what I built. I copied the Hiwatt style lead dressing and layout exactly - the only differences are a minor change in the preamp grounding based on the advice of the late Ken Fischer, and a voltage doubling circuit it the bias supply. Also - I retained the "120W" output stage.
With all 6 EL34s it makes 138 watts clean - with just 2 EL34s: 72W!
