Svetlana 6550's test low??

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Has anyone out there tested Russian Svetlana 6550C's on a Hickok 539C (175 plate volts, 1.4 volts bias, 1/4 volt AC signal for transconductance test) ? I am getting reasonably strong plate current (110-125 ma) but weak transconductance even with brand new tubes (many test at 5500-6000 umhos, significantly below 6550A spec which is 6250 umhos; maybe 6550C's have a lower spec?). I guess its possible that some of the used tubes tested may actually be nearly worn out as this reading would suggest but the 539C's "Life Test" (dropping heater voltage by 10%...all else remaining the same) shows no significant change in transconductance at all. Its also puzzeling that many new tubes test the same as the used ones with the same low transconductance test values. Any ideas or prior experiences to share?

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Topic - Svetlana 6550's test low?? - hjphjp 17:51:37 07/17/06 (1)

Re: Svetlana 6550's test low?? - shermanr@prw.net 17:42:43 07/18/06 (0)

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