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In Reply to: RE: Questions about 6BG6G amp build (schematic) Grommes 216BA posted by PeterI on May 22, 2017 at 21:02:33
Question.
How would other parameters change if I ran this tube in pentode mode, since i don't have UL taps. Tube specs say under 400V on the screen. Sourced from dropping B+ ?
Thought I'd do triode mode but looking at options.
Thanks
Follow Ups:
It's a beam power tetrode, not a true 3 grid pentode, but that's essentially semantics.
Max. open loop linearity in full pentode mode is obtained by regulating g2 B+ at a fraction of anode B+. Nasty IM distortion gets held down.
Eli D.
Thanks, I know it's a tetrode but the data sheets call it pentode mode. I see the people are tired of this thread.
Time to start drilling holes in aluminum.
Thx
before you go cutting holes, you should figure out what your g2 voltage target is...:) or leave room to do it later.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
The supply needs to be well reg'd, but it is not 'a fraction of B+' that is important, it is exactly what the combination of B+, idle point, load mixes with the effects of g2 voltage. The data OP's are for max power, probably best if you don't know why you're doing it to reduce the g2 voltages by at least 10%, maybe 15%. Depends on who wrote the data sheet.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
Probably the best AB1 operating condition for 6BG6G pentodes is 750 V 30 mA plate, 350 V regulated screen. A lot of power with very low open loop distortion. The only caveat is 10-12K output transformer. If you have super-6BG6GA tubes, those can be taken even further to 800-850V, 400V, and 40 mA, with even better results.No 6L6 version is capable of pulling such stunts.
Edits: 05/24/17
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