>
>Hi Dick...
>
>You're absolutely right - when HV is physically disconnected from both
>tubes' anodes, it's just really improbable that those mystical little gold
>balls we so often hear about -
? Mystical gold balls? According to the 'Eimac letter' on my Web site,
evaporated gold, which is caused by an oscillation condition, poisons
emission and causes leakage. (photographs of gold-sputtered tubes
appear in "Parasitics Revisited" - Sept.-Oct., 1990 *QST*)
>- the ones that infest the tubes of every amp
>not fitted with one specific type of equally-mystical parasitic suppressors
? At this point, what could be mystical about the means by which VHF
parasitic suppressors reduce the VHF-Q of the anode resonant circuit? .
- For more info, see"Parasites and Instability in Radio Transmitters" by
G. W. Fyler, General Electric Company, Proceedings of the Institute of
Radio Engineers, Vol. 23, Number 9; September, 1935. Mr. Fyler
concludes with: "... the plate or grid parasitic circuits should be
damped with resistance.". So, what could be "mystical" about using
resistance-wire to construct vhf parasitic suppressors? . . On p.72 in
the 1926 *Radio Amateur's Handbook*, F. E. Handy recommends the use of
resistance-wire to reduce parasitic oscillations. . Could this long and
winding brouhaha be related to NIH syndrome and what the Japanese call
"ringeisho"?
>-- it's just really improbable that they can cause the tube(s) to draw 75mA
of Ip!
? Indeed. I would say virtually impossible, Dick. When the leakage
current from sputtered gold is a fraction of mA, anode to (grounded) grid
arcs are likely. Anode to grounded-grid arcs tend to change the
calibration of meters - or worse.
>
>In fact, through 29 years of shipping thousands of amps using 8874/
>3CX800A7/8877 class triodes, I've personally NEVER seen a tube draw more
>than a few hundred uA of Ip under "cutoff" bias conditions.
? Semi-agreed. Gassy 4-1000As appear to be an exception.
- end -
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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