OZ5TG wrote:
> >
> >I copied this from an erlier mail. I am currently
> working with a
> >YC-156, and I have the original 3CPX5000A7 Eimac
> product sheet.
> >
> >It says warmup time minimum 6 min. without RF AND
> PLATE voltage.
> >
> >No RF, We never do that, but no plate HV, That's
> new to me.
> >
> >Any comments, other information or expiriences ??
> >
> >
> >Best regards
> >
> >OZ5TG, Vern
A couple of points here.
1) You can apply HV any time you want. Just don't
draw any cathode current during the six minute warmup.
In other words, keep the cathode biased negative with
respect to the grid until after six minutes.
The first company who used the YC-156 (Erbtec, now
Colorado Med-Tech) kept the HV turned off until after
the heater warmup time. That was their choice, and it
was merely convenient for Eimac to write it into the
specs.
Likewise for the once per day on/off cycle - the first
user of the tube planned to use it in that manner, so
it was written up in the spec sheet. You can believe
during amplifier development that I saw heaters cycled
a lot more than that, and the tubes still lasted as
long (18,000 hours) as those operated with a once per
day cycle.
2) An earlier post suggested that the six minute
warmup is because the heater is unusually small for
this size tube. Actually, this is one of the largest
heater/cathode arrangements that Eimac makes in the
oxide coated family.
The heater and cathode have a vacuum for insulation
between them. Therefore, the thermal transfer is
mostly via radiation, and is quite slow. Oxide
cathode tubes (separate heater and cathode) always
have relatively long warmup times. But there's a
benefit.
"Instant-on" tubes with thoriated-tungsten filaments
(3-500Z, 3CX1200A7, others) suffer every time the
filament is turned on and it passes through the
crystal realignment temperature region. (There's a
wonderful app note on Burle's website about this).
Therefore, "instant-on" tubes have a finite number of
turn-on cycles more or less built into them. In
broadcast service, where the filament is left on
continuously, the lifetime is remarkably higher than
in amateur service.
Hope that helps!
Dave W8NF
__________________________________________________
Do You Yahoo!?
Yahoo! Auctions - buy the things you want at great prices
http://auctions.yahoo.com/
--
FAQ on WWW: http://www.contesting.com/FAQ/amps
Submissions: amps@contesting.com
Administrative requests: amps-REQUEST@contesting.com
Problems: owner-amps@contesting.com
|