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At one time the copper pinch off was regarded as a higher quality but more expensive method of tipping off a tube, and was employed on a number of expensive special purpose tubes. The "cold weld" of the copper provides a near perfect seal, and does not out-gas during the seal process as heated glass does. Interesting to note, however that the 15GP22s employed copper pinch off. Does anybody have any data on long term leakage rates of cu pinch vs glass tip offs
jr
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