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

[Peter Chadwick]

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.

Peter W6/G3RZP