Carl, KM1H, wrote:
>....... The swamping resistance can be anywhere
>from 20 Ohms or so up to about 200 Ohms dependent upon drive available.
>With that degree of swamping neutralization is not reuired and the amp is
>completely stable.
It is generally considered to be bad luck to say the words "completely
stable", Carl. . Tempt not fate.
>Another advantage in using a more conventional circuit is that it is
>simple to include the G3SEK design screen regulator for best IMD since VR
>tubes and Zeners do not have the low impedence required for ultimate
>performance.
Not all shunt regulators are equal. Some zeners have good dynamic Z.
Some do not. You gotta do your homework. It is advisable to not exceed
1/3 of the rated dissipation. (20), high-quality, 5w, 20v zeners mounted
on a perfboard, biased with up to 80mA, will provide 400v of fairly stiff
screen potential. However, for tetrodes (8166, 8169, 8171, 8281...)
that use higher screen potentials, a 723-controlled FET pass regulator,
with a suitable screen current bleeder R to guard against
potentially-fatal reverse screen-current, has advantages. (circuit on my
Web site)
- cheers
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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