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In Reply to: just a thought... posted by Dave Cigna on March 17, 2007 at 17:36:35:
Dave,I don't know if your thinking holds up. An error correction signal is applied to g2. IF it is appropriate, things will work well.
In any case, loop NFB (hopefully only a few dB.) is needed to further lower O/P impedance and correct for "iron" flaws.
See my post down the page replying to sser2. The need to keep instantaneous plate potential above g2 potential never goes away.
Eli D.
Follow Ups:
"The need to keep instantaneous plate potential above g2 potential never goes away."That is an impossible need to meet, in either UL or pentode mode. At full signal, the plate voltage will swing from close to 0v up to twice B+. How can the screen voltage always be lower than that?
Obviously, g2 potential must remain positive. However, when the "idle" state potential difference between g2 and plate is significant, multi-grid power O/P tubes are most linear. Also, quite a bit of the distortion generated is of the HIGHLY objectionable IM variety.
Eli D.
Hi.Here what I have done to my ST-70 triode strapped EL-34.
Instead of the common practice of 100R bridging the plate & g2 I used before, I have them 32V apart by replacing it with a string of 5x6.2V zener, a SS diode & a 10R resistors.
"Most linear" or "highly objectional IM variety" generated or not, I am happy I have done so as it sounds better to me now.
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