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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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Tubes Asylum Questions about tubes and gear that glows. FAQ |
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In Reply to: If they are new tubes, posted by sser2 on December 9, 2006 at 16:08:34:
"at a given bias plate current goes prety much with Gm, so matching for equal plate current at the same biasing voltage is sufficient."I'm afraid I can't agree. I have tubes with a wide range of Gm that have very similar bias currents and vice-versa. I have NOS GE 6550A that vary as much as 1250-1500 umhos but are within a few ma. on current, for instance.
New production tubes often show the same result.
That's why I match cathode current first (at 465 volts plate and screen and -50 on the control grid for 6550A, for instance), then while the tube is blazing hot I check Gm. I can't check just current or Gm and get good matches.
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Follow Ups
- Re: If they are new tubes, - Jim McShane 09:19:16 12/10/06 (5)
- Thanks for the correction. - sser2 13:05:30 12/10/06 (4)
- Re: Thanks for the correction. - Jim McShane 14:01:31 12/10/06 (3)
- I was thinking - sser2 14:51:29 12/10/06 (2)
- Re: I was thinking - Jim McShane 15:06:58 12/10/06 (1)
- I see. - sser2 16:15:25 12/10/06 (0)
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