>Rich says:
>
> >? A filament-voltmeter for the 3-500Z, in lieu of a grid-current
> meter,
> >would have added little to the price. A 1mA DC movement would have
> >sufficed. A schottkey rectifier costs under $0.50. The most
> expensive
> >part would have been the custom AC meter scale. . Typical fil. v. in
> a
> >SB-1000 is c. 5.3v.
>
>Agreed. But perceptions come into this too. I guess many hams wouldn't know
>what do with the filament rheostat; some would turn it full up to get more
>emission,
? With a thoriated-tungsten cathode, there is virtually no increase in
output if the filament potential is increased above what is needed to
secure maximal PEP. The technique for adjusting filament potential is
exceedingly simple -- i.e., decrease fil. potential until PEP barely
drops. Increase fil. potential by 2%. By using this technique, up to
20k-hours of operation can be had between recarburizations.
> some right down for life, and then run out of emission.
? If the fil. pot. is set too low, and gas atoms contaminate the
thorium, full-emission can be restored by operating the filament at max.
rated potential for a brief interval.
>
>Funny thing, filament rheostats went out of fashion after dull emitter tubes
>came along, round about 1923-24 time. 75 years later, some of us like the
>idea of bringing them back..........
>
? The 30S-1 had one. Curiously, during the grate-debate, several
members of the Rauchian camp assured me that rheostats were not suitable
for such a purpose.
>My new amp will have a constant current supply, adjusted to get the right
>volts on the heater, with no big surge at switch on. But the SMPS for that
>was $10 at a hamfest flea market....
>
? ... good idea for a heater-type cathode.
- later, Peter
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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