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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: Transconductance Conversion RE: 12AU7/ECC82 posted by PNZ on July 24, 2006 at 19:28:22:
By definition gm = dIp/dEpand Ip = k (Eg + Ep/mu)^3/2.
Differentiating gives
gm = 3/2 k (Eg + Ep/mu)^1/2.
back substitution into the first equation gives
gm = 3/2 Ip/(Eg + Ep /mu)
So Ip = 2/3 gm .(Eg + Ep/mu)
Check with known values
Ep = 250, Eg = -8.5, mu = 17, gm = 2.2 mS
Ip = 2/3 x 2.2 x (250/17-8.5) = 9.1 against a book value of 10.5.
The error is possibly because of rounding in the handbook values or because the Child Langmuir equation ignores contact potential.
Note that you must use the values of Eg and Ep at which the gm was taken. To use different values use eqn 3 to derive k then back substitute the new values into eqn 2.
Mark Kelly
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Follow Ups
- By definition - Mark Kelly 18:51:09 07/25/06 (0)
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