[Amps] Life and gain of 3-500Z

[Tom W8JI]

> 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 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?

73 Tom