prewar Marconi

[ohohyodafarted]

Originally Posted by ppppenguin

The guns on the 9" and 12" pre-war EMI CRTs are a particularly complex hexode design. Not sure how much needs to be dismantled to replace the cathode/heater assembly.

I hadn't heard about the EHT connector problem. Possibly because the 6/6 that I had rebuilt in 1986 was pumped cold. There were 2 reasons for this. The CRT was too long to fit in the available oven and the guys doing the glassblowing were worried that the stresses caused by heating could crack the glass. I'm not sure about the stress problem, the heating might well anneal the glass and make it stronger. I admit that for that project we had a choice of 5 dead EMI 6/6 CRTs. The choice was made on the basis of which glass had the fewest bubbles and other defects.

Jeffery,

Just out of curiosity, how long did you "cold pump" that EMI crt to get a good vacuum? WE had been considering a low temperature pump down, in the range of 450 to 500F for our 15GP22 rebuilding project, but we did not get that far. We have a special epoxy that we wanted to use to seal the leaks, but it degrades around 500F so we were considering using a low temperatur pump cycle, but we had not data as to how long it may take at a lower temperature. It would be useful to know how long it takes to pump down a crt that is at low temperature versus at 650F in a pump down oven.

Thanks!