Diagnosis @shroprockdoctor found the root cause of…


Diagnosis @shroprockdoctor found the root cause of the fault to be a bad tube. The front panel monitor of output tubes gave no indication of a fault. Tubes removed, plate voltages were measured & confirmed before taking measurements with the bias probes. Manufacturer specified range is 28 – 34mA per tube. The central push pull pair were measured at 27.6mA & 59.6mA.
The outer pair measured 34.3mA & 34mA.
Changing out the center pair for a known good pair resulted in a no fault situation.
No output hum and all features operational.
The dented 220uf electrolytic appears to be unaffected by the damage.
Owner has been advised a matched quad should be installed, now awaiting confirmation.

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