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
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?
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