>
>I think that it is not "if" but "when" in Toms first statement. Most
>moving coil meters wouldn't even start to react to a minor grid current
spike. What is
>needed is the drive
>being backed off to the point that the grid can never show any current, a
>pretty impossible situation with most transceivers/amplifiers.
? Not for those who design their AB1 input configuration for their
particular transceiver.
>
>However, running a small amount of grid current in some tetrodes actually
>improves the
>IMD, the GEC data sheet for the 4CX250B recommends 250uA of grid current
>for best IMD performance.
? Unlike the 4cx600JA and 4cx1500B, the 4cx250B is not designed for
minimal grid interception. Eimac recommends no grid current in linear
operation for the 4cx250B. One look at the constant curves for the three
will illustrate why.
>
>I have learnt from many years of operating tetrodes such as the 4CX250
>that a simple
>shunt stabiliser using a bunch of zeners for the screen supply is no good
? Depends on the characteristics of the zeners and on not pushing the
ratings. . I have obtained pretty good regulation from a string of
quality 20v or so, 5w zeners that are operated at no more than 1/3 of
the dissipation rating.
> or a grid bias derived from a simple supply with a mere potential divider is
also asking
> for trouble.
? Even if the bias v is set so that no grid current flows under maximal
drive?
>
- cheers, John
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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