If a tube shorts, it could summarily melt down the unfused filament
transformer during standby. The fix is to cut the wire that applies
+110vdc to the bias contacts of the small relay.
The stock Tune-C has a breakdown potential of c. 6100v. To protect the
bandswitch from parasite-related arcing, bend the first rotor plate on
the Tune-C to uniformly reduce the clearance from the first stator to
about 2/3 of normal. After bending the first rotor plate, the measured
breekdown potential should be a bit under 4000v -- about 1000v less than
the withstanding ability of the bandswitch. Thus, the bandswitch is
automatically protected from arcing by the Tune-C. .
3A diodes should be placed across the Plate meter movement. (the grid
meter is already protected).
The 922 needs at least one, 10-ohm, 10w WW resistor in series with the
B+ to provide protection against bending filament helices during
parasites.
For operation on 160m, the HV bypass C needs to be increased by >2x.
To prevent hot switching with modern radios, faster T/R relays are
needed. See my Web site for a diagram and discussion.
good luck
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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