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In Reply to: RE: I almost won this Fisher SA-1000. posted by Michael Samra on August 07, 2016 at 12:06:39
Cool amp. I've never seen one.
As you probably know, 8417 tubes are unobtainium. I'm sure it could be biased to run on EL-34 or 6550 though.
Follow Ups:
To Mr. Samra.
Methinks he remains comfortably ahead of the curve.
"Once this was all Black Plasma and Imagination" -Michael McClure
Sorry Mike
I have NO 8417s believe or not..Since I didn't win the amp,my net worth of 8417s will still remain the same...ZERO.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
"I'm sure it could be biased to run on EL-34 or 6550 though." Biased , possibly. Driven, probably not w/o major pre-driver/driver redesign. And then you wouldn't have the SA1000 any longer.
The 8417 was the last of the consumer grade 100W power tubes released. It combined the power capabilities of the 6550 with the extraordinarily easy drive requirements of the 7591. Actually, in all important respects, the 8417 is equal to two 7591s in parallel but with somewhat greater voltage capabilities. IIRC, Fisher advertised that the 8417 was originally created for this specific amp but a few other mfgrs used it too. Both GE and Sylvania mfgd them but the Sylvanias were best by far. GEs had a tendency to run away at the slightest provocation. Guess which version is unobtainium.
Steve
You can run a 6550 or an EL34 as they are relatively close in plate resistance and plate to plate loading at the same B+..The only issue you may have is,you would probably have to mod the voltage amp or driver to make sure you are swinging enough clean driver signal,being the 6550 takes 3 times as much drive as a the 8417.The EL34 also takes considerably more to drive it but looking at the driver circuit,it is probably just a matter changing the plate load or cathode resistors,or maybe the grid leak resistors on the output tubes..I'm going to look at a schematic in a bit.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
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