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I see posts about 5687 as driver tube 1:1 transformer coupled to GM70 in SE amp. And the Gm70 running in 1200-1250V. I wonder whether the driver has enough voltage swing for this purpose??
I have my GM70 operating at 1000V.
Follow Ups:
Look into a higher mu triode-connected 7788. Look up Grego Sanquinetti's artcle on the B-52 amp in Sound Practices. Look up Romy the Cat's comments on 7788 triode-connected.
The 5687 is a GREAT tube, particulary useful in a three stage amp, but a higher mu driver tube will sound better when not pushing the amplifier, in a two stage configuration.
Jeff Medwin
operating point
The GM70 needs about 150volts peak to peak at 1000v,
so the 5687 into an IT @ 150v should be fine...so with the GM70 @ 1250V you will need 200v peak to peak, so 175v on the 5687 should be fine...
you will have to examine the exact points by ear, and plan this into your building having several voltage / bias points, say 3 different points would be helpful...
GoodLuck,
-3db
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