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In Reply to: RE: GM20 questions posted by cpotl on June 07, 2010 at 07:31:12
Hi Chris,
the resistors are in fact 51R on either side of the 50K trimmer (I have replaced the bloody awkward to access single turn board mounted trimmer with a 10 turn Vishay Cermet, side of chassis mounted for easy adjustment whilst in use !)The component labelled MV1 is an 82v MOV.
Hope this helps you somewhat....;-)
Edits: 06/09/10Follow Ups:
OK, so that's what it is! (MOV = Metal oxide varistor, right?) So it's job is really just to drop a steady 82V, putting the more negative end of the bias pot at -168V. That would seem to imply grid bias voltages in the range of about -37V to -70V as the bias pot is adjusted, which seems like the right sort of ballpark. Is there any part number on the MOV, coolhand? What kind of physical size is it, I wonder?
And for the balance, I guess the offset pot is really just making very fine adjustments to the 51+51 Ohm fixed resistor pair.
Thanks everyone, for all the help and information!
Chris
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