[NLRS] Tube testing

[Gerald Johnson]

You might be a bit hasty in tossing tubes that don't test fine instantly. With the many glass/ceramic to metal seals, a bit of vacuum leak can have occurred to make the tubes a bit gassy. Sometimes just running them with heaters alone to warm up the gettering deposit will improve the vacuum to make them useable tubes again. Say 24 to 48 hours with heater power alone (and enough air to keep the seals from overheating, probably not as much air as needed for normal operation).

W0PFP used to tell of sending some 4CX250 to Eimac through the local Eimac representative. Those tubes were not working for Jim but when they returned a significant fraction did work as if they have been reprocessed, though there were no marks on the tube to hint any mechanical had been applied. Likely they had been cooked either with heater power alone or in the production equipment that originally activated the gettering deposit to clean up the vacuum.

73, Jerry, K0CQ