|Operational test of new 23cm SSPA in 2nd part of ARRL EME Contest helped to discover insufficient cooling mainly due to very narrow forced air stream through the relatively small inlet on the SSPA frame bottom. This solution is great for leading the forced air cooling for tube PA like GS35B on 70cm or TH308 on 23cm but improper for large heatsink of SSPA. After many different trials we realized that the only cooler to do the proper job is a blower with large opening covering almost the full profile of heatsink. So, we reversed the air flow from separate blower sitting on the SSPA top cover. The air outlet from heatsink was created by lifting SSPA up on small pillars in the bottom corners – see the overall view.
The result was very satisfying. The cumulative surface temperature of each particular alumina PA block and heatsinks had not slowly raised more than close to 40 deg C after over half-hour of continuous JT operation at full power. It was necessary to use full (noisy) speed of the blower at TX, while much lower and quite silent speed was found adequate at RX. It allows full concentration on noise level EME signals, even in our very small shelter, hi.