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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: RE: Different function of 12au7s and 2 12ax7s in amplifier. posted by mcgjohn@yahoo.com on February 3, 2016 at 09:25:56:
If I might offer a couple corrections...Tubes do NOT have gain, tubes have mu, and as a result the CIRCUIT they are in has gain. Also, mu (or gain as you described it) is not expressed in db.
So in a few specialized circuits (using a stout CCS for instance) a 12AX7 might approach a gain of 100, but in a cathode follower it won't even have a gain of one.
The mu of the tubes you mentioned does vary some with the current, voltage, etc. the tube is seeing, but the "spec" is:
12AX7 - mu of 100 @ 250 plate volts
12AU7 - mu of 17 @ 250 plate volts (20 at 100 volts)
12AT7 - mu of 60 @ 250 plate volts
12AY7 - mu of 44 @ 250 plate volts (I've also see slightly different figures, but all in the 41-44 range)BTW - 40 db would be a voltage gain of 100, and 99 db would be approaching a gain of 90,000!
We've come to use mu and gain interchangeably when describing tubes, but there IS a major and important difference!!
Edits: 02/05/16
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- RE: Different function of 12au7s and 2 12ax7s in amplifier. - Jim McShane 09:16:10 02/05/16 (0)
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