> --- On Wed, 28/1/09, Dave Haupt <w8nf@yahoo.com> wrote:
> From: Dave Haupt <w8nf@yahoo.com>
> Subject: [Amps] De-gassing/de-barnacling YC-156 tubes (was Source for YC-
> 156 tubes)
> To: amps@contesting.com
> Date: Wednesday, 28 January, 2009, 10:31 PM
>
> I visited the Eimac factory in San Carlos circa 1989-1990 for the purpose
> of
> witnessing the manufacture of the YC-156 tubes, which my employer was
> using in
> production at that time. If your YC-156 has PEM nuts in the grid ring, it
> was
> built for us.
>
> IIRC, Eimac's procedure for final de-gas and de-barnacling the tube was to
> immerse it in oil (so it would not arc externally) and run the
> cathode/anode
> potential up to 20kV with a current-limiting resistor and an energy
> storage
> capacitor. They ran them this way for some number of days, with no heater
> power.
>
> At the factory, our procedure was to run them in the amp, with heater and
> HV
> applied, for 72 hours. They'd arc a half dozen times the first day, then
> settle down. Our HVPS had a very fast shut-down but no crowbar.
>
> Were I to do it in the home shack, I'd string up enough resistors to get a
> few Megohms at 100 watts, feed them into a few uF worth of capacitance at
> high
> enough voltage, and run the whole thing at about 15kV. The Joule storage
> capacity of the caps would ensure that enough energy is transferred during
> an
> "event" to adsorb the gas into the copper anode (the heated copper
> anode is the getter in the YC-156: no amount of heater operation will
> getter the
> tube), or melt off the barnacle, whichever condition causes the arc. In a
> used
> YC-156, it's more likely gas; what we witnessed in young tubes was
> proposed
> by Eimac to be the barnacle issue (aka Rocky Point Effect).
>
> Also, bear in mind that it is not possible to guarantee that a tube won't
> arc, so a responsible amplifier design is one that won't get damaged when
> an
> arc occurs.
>
> 73,
>
> Dave W8NF
>
>
>
> K7RDX wrote:
>
> >> I have purchased several YC-156A pulls from this vendor and nearly
> every one
> >> tested very good. They will exchange if you get a bad tube,however I
> suggest
> >> if building from scratch to have your tubes tested..Will save hours of
> frustration when you finially light off the new amp..Remember: Most of the
> pulls offered have been stored for several months (Or years) so de-gassing
> is a good idea before use. I test my tubes filament for rated current
> pull,hi-pot for twice rated dc voltage,and run in a cooled jig with
> filament
> >> voltage for at least 8 hrs and then hi-pot again before testing with
> hv in
> >> my amp.It`s a lot of extra work but saves other component failure in
> the
> event of a flash-over..Zonum Industries will do this procedure for around
> 100 bucks plus shipping. GL,Jim..K7RDX..
While we are on the subject of the YC-156, here is some sage advice that
Dave, W8NF sent me back in 2001 when I was building my first YC-156 amp:
1. You can apply HV any time you want. Just don't draw any cathode current
during the six-minute warm-up. IOW, keep the cathode biased negative with
respect to the grid until after sis minutes elapse. The first company who
used the YC-156 (Erbtec, now Colorado Med-Tech) kept the HV turned off until
after the heater warm-up time. That was THEIR CHOICE, and it was merely
convenient for Eimac to write it in the original specs.
(Note, Alpha chose to apply HV upon turn-on with their 77 series amps.
Perfectly okay; their choice.)
2. 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 for them that way by
Eimac in the spec. sheet. You can believe that in amplifier development that
saw heaters cycled a lot more than that, the tubes still lasted as long
(18,000 hours) as those operated with a once per day cycle. Hams need not
worry about this spec. either.
3. Some suggest that the six-minute warm-up time on the YC-156 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 its 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 warm-up times. THIS IA A BENEFIT: "Instant-on" tubes with
thoriated-tungsten filaments (3-500Z, 3CX1200A7, 3-1000Z, and others) suffer
every time the filament is turned on and it passes through the crystal
realignment region. (There is a wonderful app. Note on Burle's website about
this.) Therefore, "instant-on" tubes have a finite number4 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.
I hope this info from Dave has answered some of your questions about heaters
vs. filaments on this group.
(((73)))
Phil, K5PC
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|