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In Reply to: RE: Questions about 6BG6G amp build (schematic) Grommes 216BA posted by Michael Samra on May 23, 2017 at 03:13:29
For a given amount of FB, the longer the path the less stable. The RCA SP10 and 20 used a similar topology, and had no global loop.
Aside from the idea of building with 12AU7 because that is what is on the original, bean countered schematic...well, good luck wid that. Or, build, learn, and then decide how to apply what you learned for further improvement...LOL
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Follow Ups:
I agree but look at the iron in the SP20.It is humongous and the amp is low power.All I'm saying is, Grommes used that output trafo with GFB and loop FB to the driver and much of that was probably to compensate for the output trafo. I havven't seen the OPT trafo in the amp but if he runs it at full power and bandwidth,he may run into problems.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Edits: 05/24/17
This is what I'd do. You may end up liking the 12AU7.
I may. A surprising number of high-end preamp/amp manufacturers still use 12AU7 tubes. They aren't doing it because they're beancounters.
Thanks for "input" :)
In a preamp they are fine but in an amp where the driver is much more demanding,there I would use a 6CG7.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
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