Sound City PA 120 / Hiwatt DR103 Conversion

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!  

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