The tubes (3-500z`s) were from RF Parts. I replaced (Henry 3K repair
job)some low hr Eimacs that one had developed a grid to filament short. Gain
was compared to a nos pair of Eimac`s.Higher zsac for a given Ep and close
to 10% more output for a given value of drive.Jim..
----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: "k7rdx" <k7rdx@charter.net>; "Amps" <amps@contesting.com>
Sent: Tuesday, July 18, 2006 3:14 AM
Subject: Life and gain of 3-500Z
> > 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
>
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