It was more of a trademark of Arcturus during the late 20s early 30s. They went to standard clear glass after then so they can be a bit rare. Saw some of the No.071 go for 50-150 dollars each on ebay.
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3D21 (WA) grounded screen looks interesting, maybe for driving directly electrostat speakers ... STAX...
not sure if this is great idea, but...
realize a fat tetrode se, with direct coupled screen drive, and grid driven from opt secondary (potentiometer, variable fb to match "taste")
"not sure if this is great idea, but..."
Yes, after thinking about such an approach, I realized that it would make the screen drive much more difficult, by requiring higher g2 drive to conteract the g1 NFDBK (causing screen current to become excessive).
A fix would be to only use just the error as feedback (unlike conventional feedback, this would pre-subtract the scaled output and input to get the small difference. Sometimes called Hawksford EC) That would likely solve the screen drive issue with only a tiny correction on g1.
But....., once one goes to the trouble of making a subtractor stage for the EC signal, it is already so effective in conventional NFDBK form as to not need the advantage of the finite Fdbk level with the g2 drive/g1 feedback idea.
Yes, after thinking about such an approach, I realized that it would make the screen drive much more difficult, by requiring higher g2 drive to conteract the g1 NFDBK (causing screen current to become excessive).
A fix would be to only use just the error as feedback (unlike conventional feedback, this would pre-subtract the scaled output and input to get the small difference. Sometimes called Hawksford EC) That would likely solve the screen drive issue with only a tiny correction on g1.
But....., once one goes to the trouble of making a subtractor stage for the EC signal, it is already so effective in conventional NFDBK form as to not need the advantage of the finite Fdbk level with the g2 drive/g1 feedback idea.
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