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interested in the physical description of this tube type. Are the plates of a 12A_7 usually between two mica spacers or what?
Follow Ups:
Heres a pic from a current EBAY auction I just stumbled across. In it you can see the third mica spacer just below the edge of the getter near the top of the tube. Note that there is a small gap between it and the upper mica spacer attached to the plates. In tubes of this design the getter halo is typically bent down at an angle so that it touches this upper spacer - presumably to damn out resonances in order to make the tube less microphonic.And yes, 12A_7 family tubes just have a mica spacer above and below the plates - the third spacer is only found on some low noise versions of these tubes like 5751s and 5814s. Note that later production versions of these tubes usually ommitted the upper spacer, presumably as a cost cutting measure...
joe
That is what i thought. I will keep my eye out.
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