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
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