----- Original Message -----
From: "Phil Clements" <philc@texascellnet.com>
To: <amps@contesting.com>
Sent: Wednesday, January 28, 2009 9:08 PM
Subject: Re: [Amps] De-gassing/de-barnacling YC-156 tubes (was
SourceforYC-156 tubes)
>
>> --- 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
Adding to the above, the YC-156, and others that look identical but
tested to different specs and a different YC #, use the 3CX15000B7
internals and the 3CX5000A7 anode.
Carl
KM1H
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