On Thu, 3 Sep 98 17:00:34 -0800 Rich Measures <measures@vc.net> writes:
>
>
>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.
I consider no failures since I built it in 1965 "completely stable" Rich.
Other than PS cap replacements a few years ago the only other maintenance
was to replace the original 1964 date code 8122's last year when the
output got down to 700W.
>
>>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.
Well, Ive been off here abt 4 months since my PC took a lightning hit so
I may have missed some things.
BUT I do remember you being very adamant at one time about the horrible
performance of Zeners and most active SS regulators. Have you changed
your mind recently?
I do know that the G3SEK regulator as installed in my NCL-2000 has made a
impressive performance improvement in IMD. From -28/-32 to -33/-38
3rd/5th respectively with no other changes to the amp. Not bad IMO for
old design tetrodes.
73 Carl KM1H
Amplifier Repair and 6M Conversions Our Speciality
(circuit on
>my
>Web site)
>- cheers
>
>
>
>Rich...
>
>R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
>
>
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>
>
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