Hello to All:
I feel that one can use the available literature that Eimac published
decades ago on this topic. If you go to their web site, they currently list
an article on exactly this topic.
To cut to the quick, keep the filament voltage within the Eimac datasheet
range. Everything already commented on is substantiated in their AP-19
bulletin.
I downloaded a copy years ago; I have it in my file. It is a good article
to read and documents tube life versus voltage.
Go to the following link on the Eimac web site and read the information:
http://www.cpii.com/docs/related/22/AB18.pdf
It will provide useful information for all.
Chuck W9POU
-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
Behalf Of Alek Petkovic
Sent: Thursday, January 28, 2010 4:06 PM
To: Rob Stampfli; Amps Listserve
Subject: Re: [Amps] Ameritron (et. al.) filament voltages
G'day Rob
It is not any "camp" that makes the claim of shortened emissive life
due to high filament voltage. It is Eimac, in its "Care And Feeding"
book. For every 3% increased in filament voltage, the life is
shortened by 50%. In the case of Ameritron's 10%, one would expect
around 12% of normal tube life. (Didn't someone recommend Ameritron
here a couple of days ago on a different thread? Ha ha)
Yaesu have the same problem with the 2100 series amps. Even when the
mains input voltage is reduced to the specified 230 Volts, the
filament voltage still needs to come down.
Like you, I have made the correction with every amp that has ever had
the lid removed in this house.
73, Alek
VK6APK
At 03:29 AM 29/01/2010, Rob Stampfli wrote:
>On Thu, Jan 28, 2010 at 03:10:46PM +0800, Alek Petkovic wrote:
> > Just as an aside. When the amp is run on 245V AC, here in Australia,
> > the voltage measured on the filament pins, with all 4 tubes lit up,
> > is 7.15V AC. A bit on the high side you could say. Could even call it
> > scandalous.
>
>I've noticed the same here with an AL-80B: On 240V, the filament
>voltage runs >5.5V on a 3-500Z (nominally a 5V tube). I spoke with
>Ameritron on the phone about the issue and their tech told me that
>voltages up to 5.6V are considered normal.
>
>I understand that high filament voltages is a contentious issue among
>hams and amp manufacturers. One camp claims it drastically shortens
>the tube life, whereas the other claims that in ICAS operation that
>other factors will kill a tube long before the excess filament voltage
>will do so.
>
>I remain curious, though: What is to be gained by designing amps that
>run 10+% high on filament voltages? (And, frankly, I've never heard
>of a commerical amp that runs low.)
>
>FWIW, I tacked a few current-sensing resistors into the circuit to
>lower my tube's filament to a more nominal 5V, and have not noticed
>any problems from having done so here, but YMMV.
>
>Rob / KD8WK
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