My 4k resistor or light bulb test is based on the ohms law of the plate voltage and the cathode current so dont apply that to your bw set
Im going on 400 volts at 220ma.
One thing I coulldnt recommend enough is a bk 1077 for these issues. It pretty much instantly isolates the problem.
Not to hijack the thread but I would be interested in hearing about your bw set.
We really cant have enough discussion on HV issues. It has always been the biggest issue with sets and looking through old trade mags verifies that.