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Re: [Amps] Warm up and on time question...

Subject: Re: [Amps] Warm up and on time question...
From: "Roger (K8RI)" <>
Date: Sat, 17 Dec 2011 04:45:17 -0500
List-post: <">>
On 12/14/2011 8:49 PM, BJ VOUTE wrote:
> Is there an official Eimac or other tube manufacturer data sheet that 
> specifies warm-up/cool-down for a 3-500?  I looked at an Eimac 3-500 sheet 
> and must have missed it?
The data sheets  I have do not list any warm up times. IOW, throw the 
switch and go.  It does state that Inrush current should be limited to 
two times normal current during turn on to limit thermal stress which 
could cause changes to the internal tube geometry. IE either current 
limiting, step start, or ramp up.  I found nothing on shut down cooling.

My question then becomes one of, is there anything to be gained by 
"extending warm up times beyond the prevention of excessive inrush 
current when firing up?"

With external anode tubes and particularly the larger tubes we know that 
they continue to get hotter when the fan and power are killed at the 
same time.
Then I have to ask, does this increase in temp cause any problems, or 
are we adding unnecessary complexity by extending the fan run time after 
the filament is turned off. Do we gain anything in tube life by doing 
so?  I can understand where inrush current and stress is taken into 
account and "Possibly" shock cooling.   OTOH do we gain anything by 
doing this with much less massive tubes like the 8877, 3CX800, or even 
the Chinese FU728F?


Roger (K8RI)

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