[ohohyodafarted]

There is also another consideration in the rebuilding of a 15G which could potentially be a very large problem.

Some years ago John Folsom and I had Scotty at Hawkeye rebuild a 15G which, up to that time, had been leak free. Scotty successfully installed a rebuilg 15G gun assembly and evacuated the tube using a slow ramp 6 hour evacuation cycle in his oven.

The rebuild was a success and the tube was shipped to Florida where John Folsom and I installed it in a 15" Westinghouse set. It produced a beautiful picture for a short period. 30 days later the tube had become gassy. We surmise that somehow during the evacuation cycle the stresses of temperature and physical forces involved in relieving the original vacuum, and then pulling a new vacuum on the envelope, caused some sort of defect in the envelope. We have not pulled the tube to examine it and determine exactly what kind of leak it has, but that is something that we will need to do before proceeding on any further attempts to rebuild a 15G.

There is the possibility that the envelope had a micro crack that propagated due to heat and physical stresses. And it should be noted that we had sealed the envelope with VacSeal which points to the complete ineffectiveness of using VacSeal to eliminate vacuum leaks on a 15G.

John Yurkon and I have discussed the possibility of doing a very long low temperature evacuation. By not subjecting the envelope to such high temperatures, the amount of stress from thermal expansion and contraction would be reduced, and hopefully this would help to minimize the tendency to cause a physical defect in the envelope. It would also help protect the phosphor dot plate from cracking like occurred in several tubes that RACS worked on.