[Amps] Gettering 572B
jtml at losalamos.com
Tue Jun 23 06:36:57 PDT 2009
Sounds like some internet 'folklore' has become interjected with
conditioning of large power tubes. With large tubes, it is imperative to
condition them before first use, and if they sit for a long time without
being pumped. We do this at work, under instruction from Burle
Industries and CPI/Eimac. I am talking about tubes that are big enough
to require some strain when carrying them, or using a crane. They have
such large envelopes that there can be gas molecules in sufficient
quantity, or they may have very small seal leaks. In these, the filament
is turned up to normal, then the HV is slowly applied slowly first, to
knock off whiskers or other particles, to reduce ionic collisions inside
the tube. The ionized molecules will hopefully go into the getter. Then
beam (Ip) is increased along with other grid currents to heat the
elements and allow more outgassing that is collected in the getters
inside the tube, or in external ion pumps on really big tubes such as
type 4616 tetrode, 7835 triode, 8974 tetrode, etc.
For little tubes, that fit in your hand, the getter is also inside the
tube. They may be either cold or hot getters in that they work all the
time but most effectively when the filament is heated. There is no need
to slowly apply filament for them however, full on heat is adequate to
make them effective. (on big tubes, applying lower than normal filament
temperatures is detrimental to the gas evolution, as carbon monoxide and
other gases may get released if not careful at lower than 1900 Kelvin.
(thoriated tungsten temp). This depends on the design of the heaters.
For a tube such as 4CX3000 and up, 30 minutes of filament only operation
without HV, then normal HV or reduced HV for a few minutes is perfect
for making sure the molecules are adsorbed into the getter. What you
don't want is for ionizations to occur in quantity and go ripping back
to the cathode to damage the carburization layer on top of the TT.
In my opinion, doing this slow heatup that you describe, is wasteful of
time and accomplishes little that can't be done with normal 30 min.
first-time turn on. Its unfortunate that amplifier manufacturers have
propagated such mythological advice on users. But, like the special
cables for audio and special cloths for DVD's, there you are.
Sorry to come down hard on this practice, but its first time i have
heard it here, and I have been running-in new RF power tubes in my work
for over 30 years - in broadcast, industrial and scientific sockets. It
certainly doesn't hurt to do it your way, except for the concern over
running the filament too cold for some hours and creating MORE gas
inside tubes. I would welcome advice from Eimac on this fact, as perhaps
smaller TT heaters don't have this problem that big filament bars seem
Bill English wrote:
> Hi John
> I am under the impression to properly "getter" a tube, you need to remove
> the HV, only use filament voltage, and it is best done by starting out with
> a lowered filament and slowly bring it up over a period of hours to the
> normal fil. voltage, then letting it "cook". I have heard from 24 hours to
> as long as 36 hours. This process removes gases and impurities in tubes that
> have sat stored for long periods.
> I know that some companies will only warranty amps with tubes that were
> properly "gettered" by them, and running your own tubes can void the
> warranty should you have a problem. I am pretty sure QRO is one that does.
> Bill K4FX
> -----Original Message-----
> From: amps-bounces at contesting.com [mailto:amps-bounces at contesting.com]On
> Behalf Of John Lyles
> Sent: Monday, June 22, 2009 12:54 AM
> To: amps at contesting.com
> Subject: [Amps] Gettering 572B
> What exactly do you mean by the term 'gettering'. I know what a getter is,
> inside a tube, but I have never heard of being able to getter a tube,
> i.e., as a verb. If HV was on when you were in standby, depending on
> your cutoff bias, or idling bias, would control the amount of Ip. Could
> you explain what the condition was, cutoff bias or some amount of
> conduction (like zero signal anode current?). I guess this depends on
> how your radio defines 'standby'.
>> Message: 4
>> Date: Sat, 20 Jun 2009 20:56:03 -0500
>> From: Larry K4AB <larry.k4ab at gmail.com>
>> Subject: [Amps] Gettering 572B
>> To: amps at contesting.com
>> <5b335b050906201856u3ac6f2a9n9e81a5e05214757c at mail.gmail.com>
>> Content-Type: text/plain; charset=ISO-8859-1
>> I noticed when gettering a new set of 572B's that I was drawing about
>> Ip during standby.
>> I quicky turned off the juice.
>> 1) Should I continue the gettering with the plate caps removed?
>> 2) Is gettering even necessary with high quality tubes?
>> 3) Are,(at least one of tubes) bad?
>> Larry K4AB
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