Mind the gap! RCA 10BP4 failure

[Penthode]

Something blew the cathode connection wide open.

My guess is the CRT tester rejuvenator. When the cathode weld failed and the rejuvenation process was applied, the blast blew the cathode wide open.

[Alex KL-1]

Ah, I considered the normal usage and perhaps I read too fast the text... yes, make sense, I also bet this (the tester) or one trying to manually re-welding the cathode...

[Penthode]

Deleted post

[Tim Tress]

In almost 50 years, I have encountered two 10BP4s with the same problem; the filament lights, but there is absolutely no emission. Both were from late 1940s sets, so maybe there were some issues during manufacturing.

[Penthode]

Check the cathode connection in the tube. My observation is the cathode opening due to a burst of high current which is enough to melt the fine metal link to the cathode pin of the kinescope.

[Chris K]

I guess a gap of that size means it's hopeless to try to reweld the cathode using that function in many rejuvenators, even with vigorous shocking of the CRT neck?

[Electronic M]

Originally Posted by Chris K

I guess a gap of that size means it's hopeless to try to reweld the cathode using that function in many rejuvenators, even with vigorous shocking of the CRT neck?

I wonder if the metal is ferrous enough that a VERY Strong magnet could be used to pull the more flexible side of the break close enough for a weld function to work.