[Amps] 3-500 / 4-400 cooling (09/10/2005)

[R.Measures]

On Jan 30, 2006, at 4:56 PM, Peter Chadwick wrote:

> The British (and a few other armies') D11 and D13 transmitters cooled 
> 4-125 (D11) and 4-250 (D13) by blowing air from the top. They suffered 
> badly from this socket problem. If you figure that Eimac didn't sell 
> chimneys for 4-400s because they weren't needed, you can reach the 
> conclusion that they were meant to be blown from below. Air goes 
> through the holes in the ceramic sockets and out through the holes in 
> the metal base ring, cooling the filament (and other pins) on the way, 
> and then goes over the envelope and past the heat dissipating plate 
> connector before exhausting. Tubes like the European QY4 250 etc don't 
> have the metal base ring, and so are much harder to cool. As was said, 
> one answer is to use small fans cooling the socket side, while another 
> is to arrange cooling to come from underneath and use a chimney. I use 
> a 4 inch Muffin fan on each tube base of my 2 tube 4-250 amp,  as well 
> as an 8 inch fan blowing straight down on the plate caps. Seems to 
> work.

Thanks to the laws of aerodynamics, blowing air from the side results 
in cooler operating temperatures of glass envelope, radiation-cooled 
tubes.  However, for a 4-250A, et-cetera, at least a 150mm dia. fan and 
an open-ended chassis are needed.  Also, the fan blades need to dip 
about  25mm below the level of the socket to direct air at pins #1 and 
#5 -- the filaments.
>
> Peter W6/G3RZP
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>

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org