In Reply to: Where can I find the list of octal tubes with Mu over 100? posted by Iczerman on August 21, 2012 at 11:56:25:
If you take a normal pentode or beam-power tube and connect the two grids (control and screen) together (not the usual triode connection), you will get an extremely high mu factor. So high that the grid cut-off voltage will be very low. However, the plate voltage is not limited to the maximum screen voltage, as in the normal plate-screen connection for triode use.
For an example, see the high-voltage power supply on page 382 of Elmore and Sands, "Electronics: Experimental Techniques", McGraw Hill 1949 (National Nuclear Energy Series, Manhattan Project Technical Section). This power supply uses two 807s, each connected per above, to make high-mu high-voltage triodes. In that example, mu = 350 and gm = 2000 umho. Since the 807 is not octal, try 6L6 or 6BG6 for almost the same result. I would be curious to see the result with a lower-power pentode such as 6AC7 or 6SJ7.
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Follow Ups
- RE: Where can I find the list of octal tubes with Mu over 100? - TimFox 12:03:40 08/29/12 (0)