02-12-2007, 05:50 PM
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Join Date: Apr 2005
Originally Posted by ken white
Larry, the part in question looks like an air dielectric variable capacitor to me, not a roller inductor. So, the part that is missing was probably a capacitor added across some of the plates to increase its base value. But it is very hard to tell from the picture...
The diagram shows a 120 pf (gotta be HV part, not some 600 volt mica jobbie) capacitor to ground in parallel with the load variable. Also at that point, you also have a 10 pf cap going over to metering circuit, a 10 pf cap going to the RF indicator (#3 neon lamp) and, a 22 micro-henry choke to ground.
Set the load variable to full mesh and tune the amp for max DK; look at the Tune variable, it should be somewhere near half meshed. Now, adjust the load variable for max output if, the capacitor is fully closed then you need that external 120 pf part installed.
The tubes are 12 pin 20LF6s, the final tubes are strung across the AC power line to light the filaments. Have somebody with a tube checker go thru the tubes, they check just like a 6LF6 only with a 20 volt filament.