On Jul 18, 2006, at 3:14 AM, Tom W8JI wrote:
>> Agreed Tom...My question was why would someone run an amp
>> with that value of
>> line voltage if he knew the effect it would have on the
>> fils.
>
> The filament life issue is primarily an issue with good
> manufacturing quality and steady operation at conservative
> values.
>
> Say you run a tube 24/7/52. In a week you have 168 hours. In
> a year 8736 hours. There is no thermal cycling. There is no
> time for the pin seals to get moist and oxidize ruining the
> glass bond. There are no overtemperature operation or even
> operation anywhere close to seal rating. The tube is
> constantly being gettered. All we have is the filament
> erroding away
As a thoriated tungsten filament ages, carbon atoms slowly depart
from the ditungsten carbide (W^2C) emissive-layer, leaving tungsten
behind. Since tungsten is more conductive than ditungsten carbide,
the resistance of the filament gradually decreases as it ages. This
decrease in R is used during carburizatation of the tungsten filament
to indicate the thickness of emissive layer's thickness, and when to
shut off the acetylene. As I understand it, the difference in R
between a carburized filament and an uncarburized one is c. 4%
> or losing emission from temperature. Emission
> life is critical.
>
> If we turn the amp on 3 hours a day, transmit 25% of the
> time with varying power, let the thing sit for a week
> without use once in a while, and occasionally run the seal
> temps up to maximum, and use (by force now) poor quality
> tubes we have a whole different set of likely failures. The
> data points from and important to commercial service do not
> apply the same way.
>
>> I do know for a
>> fact that a lot of the Chinese 3-500z tubes have higher
>> gain than the older
>> Eimacs
>
> I'm not saying that isn't true, but I never saw that happen
> at the transition time when Eimac went out of the glass
> power grid business and I started looking at Chinese tubes.
> I'm not trying to start another long argumentative thread
> like the tube curve thread, but rather to learn something.
> How did you measure gain and where did the tubes come from?
A reliable gauge of Mu / amplification factor is ZSAC. Less ZSAC at
a given anode potential for the same cathode/grid bias V =s more Mu.
>
> 73 Tom
>
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
>
R L MEASURES, AG6K. 805-386-3734
r@somis.org
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|