The only thing that matters is that the replacement fan conform to the
dimensions of the original so it can be mounted with the factory
drilled or punched screw holes, and that it _at least_ blow the CFM of
the original _or more_. To be honest, most factory fans do not really
move enough air. Most hams are nowadays non-technical consumers, they
demand "quiet" amps, and manufacturers have no choice but to supply
minimal cooling in order to sell their products. Therefore, beyond
the minimum, the CFM spec. isn't critical. You'd probably be better
off with higher air movement, especially for continuous duty, but your
non-technical obsession with having a replacement exactly conform to
the original in every way is limiting your choices needlessly. I
suggest you study RF PA air cooling and examine other RF amplifiers,
especially those made for commercial continuous duty. Bill Orr once
famously remarked that you don't have enough air until the tubes get
blown out of their sockets, then you can back off some. I'm
paraphrasing, but that was generally his message.
73
Rob
K5UJ
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