As several people predicted, my pair of GU74B's does not
seem to have been damaged by accidentally running them
without filament voltage. All is fixed now.
Incidentally, this amp is a TenTec Titan III, Model 417. The
TenTec service tech says this is not the first time they
have seen this failure in the filament wiring. They
recommend, and routinely install, a modification to route
the filament transformer leads more directly to the tubes,
thereby eliminating a pair of wimpy plugs/sockets in the
cabling:
1. Unsolder the two green filament transformer leads from
the Screen Supply Board.
2. Using #18 wire, extend those filament transformer leads,
bringing them to terminals P1 and P3 on the Input Match
Board, where the tube filaments are connected.
Did the mod. 50W in / 1500W out. Thanks for your help.
Dave Hachadorian, K6LL
Yuma, AZ
.
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