by EWBrown » Thu Mar 11, 2004 6:55 am
I haven't yet finished the article, are they referring to the screen grid loading resistance or impedance? If it is impedance then they are referring to the tap position on the OPT, which is pretty standardized at 40-43% of the number of turns from B+ (CT). That would be about 16-18.4% impedance of the plate impedance (square of the turns ratio).
In a 7600 ohm P-P OPT tranny like used in the ST-35 and DIY35, the impedance of one plate to the B+ would be 1900 ohms (1/4 the total P-P impedance) and the SG taps, assuming 43%, would be about 342 ohms to B+, and 1368 ohms SG-SG.
When one adds a resistor in series with the SG tap, then the equations get a little more complex.
I've seen SG stop resistors between 100 and 1000 ohms for SE amps, "pentode" P-P amps and in some UL circuits, though this is not as common in the latter
/ed brown .
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