[Amps] Ameritron (et. al.) filament voltages

[Rob Stampfli]

Hi Alek,
Thanks for the response.  Personally, I agree with you that it is better
to keep the filament voltages in check for a number of reasons.  However,
here's a pointer to a post (from this list) that takes the opposite
perspective:

http://lists.contesting.com/archives//html/Amps/2007-07/msg00367.html

Tom is Tom Rauch, who had a hand in the design the AL-80B, and who
certainly knows more about building amps than I ever will.  Note he's
not disputing the Eimac claim, only counter-claiming that the hazards of
ICAS operation will typically kill the tube before an over hot filament
will.  He may well be right, but I still can't see any advantage to
running excessive voltages on the filament.  That's why I cut mine back.

I put the question to the list in hopes that someone could explain why
commercial amps always seem to be designed for higher filament voltages.
The only advantage I can see is that it gives the amp more headroom in
the event of low line voltage or soft line voltage that falls excessively
under load.  Does anyone know of any additional advantages?

Inquiring minds...
Rob / KD8WK

On Fri, Jan 29, 2010 at 06:05:43AM +0800, Alek Petkovic wrote:
> 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