Super Reverb Blackface Mod Question

Pro Audio Asylum

Pro studio recording equipment and music production/industry.

A friend of mine asked me to take a look at his 1970 Fender Super Reverb, AA270 circuit; he's had problems with an output tube going into thermal runaway. He told me (several times) that he'd had the amp converted to Blackface specs by a previous tech, which, as far as I've been able to discover means making the relatively minor, but sonically significant circuit changes to the AB763 circuit.

The amp had been converted to adjustable bias and had the 100k 6L6GC grid resistors changed to 220k, but the PI plate resistors were still both 47k rather than 82k/100k. To my mind, changing the phase inverter resistor values seems one of the more significant parts of the mod--other than snipping the shunt capacitors on the 6L6GC grids.

Since I'm ignorant of this, did my friend get what he paid for when he paid for a "Blackface Mod" if the tech left the 12AT7 phase inverter plate resistors at their AA270 circuit values? To change one circuit to another makes sense to me. To change it halfway, but not all the way leaves me puzzled.

David

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Topic - Super Reverb Blackface Mod Question - Thermionic27609 08:38:16 07/03/09 (3)

RE: Super Reverb Blackface Mod Question - FenderLover 03:41:53 07/17/09 (0)

RE: Super Reverb Blackface Mod Question - DMW 18:36:23 07/07/09 (0)

RE: Super Reverb Blackface Mod Question - Pro Sound Guy 07:17:29 07/07/09 (0)

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