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RE: cloning the Fisher




I took a quick look at the AA-100 schematic. The O/P "iron" lacks ultralinear taps. Your mode choices for the "finals" are either pure pentode or triode. If (as seems likely) you go pentode mode, definitely regulate the g2 B+.

Given the 7.5 Kohm primary, you could build a pentode mode "El Cheapo". The magnetic headroom is not suspect with these transformers. BTW, the only change needed for EL84 "finals" is the cathode bias resistor value.

In addition to Heath and Fisher, inspiration may be found in the Sherwood 5000. Sherwood "cranked" the 7189 "finals" pretty hard and the AA-100 trafos would be fine in a similar regime. A true 7189 equivalent, the current production Russian 6П14П-EB (6p14p-ev), AKA EL84M, is tougher than the proverbial brick outhouse and has quite decent sonics.


Eli D.

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