[Amps] cooling tubes

[Gudguyham at aol.com]

Nice thread on the vapor cooled Eimac tube, but  I have an experience  I'd 
like to share and see if anyone can comment.  Some time ago I had  occasion to 
work on an Alpha 374 amp.  This amp has a pair of 3CX400's  (8874's)  That is a 
total plate dissipation of 800 watts similar to a  single 3CX800.  Anyway, 
this Alpha 374 cools these 2 tubes  by  pressurizing the entire RF compartment 
with a large muffin fan, the only air  escape is through a hole in the small 
chassis that the tubes are installed on  and then up through the tubes and out 
the top of the cabinet.  This amp  does not use a blower per se.  The question 
is could a muffin fan cool a  single 3CX800 tube "if" the fan was mounted 
right under a chassis that housed  the tube socket and then the only means of 
escape for the air was up through the  fins of the tube?  I understand the concept 
of air flow and that a back  pressure is a factor, but in this Alpha amp it 
seems to work.   Lou