[AMPS] Collin 30L1 Problem

[W5ASP]

We have a Collins 30L1 with a new Peter Dahl transformer installed.  The unit
turns on just fine and the filaments light up. (New tubes and filter caps.)
Tuning is as expected and RF power output is per spec.  But after 5-15 minutes
of use (heating up), the tube plate current just cuts off like a light switch.

Probing the lower voltage circuits suggests that the bias switching is being
controlled okay. It is almost as if the plate voltage or the B- path is
suddenly going away. Has anyone seen this sort of probvlem before? Any
suggestions as to what to do.  Maybe replace the plate choke ?

Appreciate the help

Joe, W5ASP


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