[Amps] Fiament watts

[Dr. David Kirkby]

On 08/30/10 10:26 AM, Han Higasa wrote:
> Hi Gents,
>
> Thanks for the list of various compelling
> tubes. Its very nice to see the list for the next HPA
> project.
>
> Now, may I ask you one question?
>
> Do you think direct heat tubes such as
> those noted as "Instant on /w a soft start required"
> will provide really the instant start capability?
>
> As one of six-meter DXers I am also using
> a direct heat tube in my HB HPA for a 'scramble
> start' with 5 seconds of filament step-start.
>
> But some authorities say one should wait until
> the entire tube being warmed up to avoid a
> mechanical stress caused by partial heat;
> larger the tube, longer the warm-up time;

That sounds dubious to me.

As soon as a tube start dissipating a kW on the anode, temperature gradients 
will exist which will be far greater than that caused by the heater warming the 
whole tube.

There's a good few data sheets at

http://www.g8wrb.org/

I just checked. The largest I have is 1 MW dissipation. Take a read.

dave