[Elecraft] KPA-500 fan noise

[Jim Brown]

On 6/2/2014 7:55 PM, Richard L Diddams, Sr. wrote:
> My comment is not to K6GPW, but to the continuously number of postings regarding Fan Noise.

Far more than necessary, IMO.  Dick, the fan speed is adjusted by the 
control system based on temperature of the output devices, which you can 
monitor from the front panel. The fan speed gradually increases as the 
temperature passes lower temperature thresholds, but it really kicks 
into high gear at about 71 degrees C.

If you want to hear what this sounds like, put a brick on the key and 
crank the amp to rated power for a minute or so. Depending on ambient 
and air flow in your shack, you'll hear it kick in, and if you have the 
instrumentation to do so, can measure it yourself.

My fan kicks in roughly 40-45 seconds into a keydown transmission on 6M, 
and very occasionally, briefly, when I'm RTTY contesting, calling CQ 
near the end of the contest with few responses. In normal contesting, 
where you're sitting on a frequency and running stations at several a 
minute, the duty cycle is low enough that the high fan speed rarely 
kicks in.

Could the noise level be reduced by some design advice from a good 
acoustic consultant? Sure. I can recommend several who work on making 
HVAC systems in theaters and concert halls dead quiet. How much cost 
would you like to add to your KPA500?

The sound pressure level at that high is nothing more than annoying, 
certainly nothing to be alarmed about from a hearing damage point of 
view, and it's a lot less annoying if you're wearing cans. And for 
keydown modes like AM, FM, PSK, and RTTY, there's even a side benefit -- 
when the fan speeds up, you've probably been going on too long about 
nothing, so it works to prevent you from boring the other member(s) of 
the QSO.

73, Jim K9YC