I noticed the same thing on my amps. The RF Parts 3-500ZGs had more output in
both my TL-922 and the Henry. The first set of Eimacs (that were in the
TL-922) had bad plate welds that eventually shorted the Anode directly to the
Grids melting the Grid choke. Replaced them with more C and carbon grid-fuse R
(per Rich's mods) and all was happy again (after installing the RFP tubes, of
course). When I got the Henry, it came with Eimacs that also had less output.
The RFP tubes are now several years old, and still do full output (~2.5kW) in
the Henry after many longwinded legal-limit AM transmissions (measured in hours
of total on-air time), several contests, etc. I was tempted to buy another set
of these to have as spares, but they have proven so reliable, I never have.
Maybe when they start to look "tired", I'll pull the trigger...
Joe, N3JI
----- Original Message ----
From: k7rdx <k7rdx@charter.net>
To: Tom W8JI <w8ji@w8ji.com>; Amps <amps@contesting.com>
Sent: Tuesday, July 18, 2006 9:09:15 AM
Subject: Re: [Amps] Life and gain of 3-500Z
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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