>=80 With Eimac's *Care and Feeding of Power Grid Tubes* formulae, Q is
>Definined as RL divided by the reactance of C1. There is no
approximation.
Eimac neglected to alert the reader to the fact that they used an
approximation.
For in depth discussions on the subject see:
Ham Radio September 1977 pp. 30-39 plus a correction in the December
issue p. 68
or
QST August 1983 pp. 23-29
Now, if only the various authors could agree on the component
designators.... sigh.
>- On my Web site, there is an Excel 4 worksheet that performs
>mathematically precise solutions to the Care and Feeding calculations
for
>those who are disinclined to exert themselves.
Precise solutions to imprecise equations are the stuff which made
computer's famous.
The values are close enough if the operating Q is sufficiently high
(>10) and considering tube capacitance plus circuit strays the errors
typically go unnoticed in the real world.
If you try to apply those formulas to low Q circuits (i.e. a cathode
matching network) then the errors will become grossly apparent.
73,
Marv WC6W
*
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