[Elecraft] Power Supply Hummmm

[Ron D'Eau Claire]

I have a couple of Astrons - the largest being a 20 amp unit - and I can
barely hear a slight hum with my ear up against the case. And my hearing
is good enough that the cooling fan on the KPA100 is very irritating,
even with phones on. We used to supply 8 amp Astrons with land mobile
"base" stations for businesses and about one out of 50 or so would get a
"hum" complaint at some point. 

I suspect something comes loose in SOME supplies. Traditionally, it is
the laminations in the transformer working loose over long periods of
use, but I suppose that it could be the case vibrating if some screws
aren't fully tightened down.

SOME Astrons are very quiet. I suspect that SOME of any type of power
supply that uses a big hunk of iron are going to hummmmmmm.

Ron AC7AC
K2 # 1289

John, K7SVV wrote:
 I have owned two Astron supplies over the years and they both made an
objectionable audible hum with or without a load.  The first one I had
was rather small 10-12 amps and I don't recall the model number but the
second one was an RS-35.  I ended up replacing it with an Alinco
DM-340MV which I feel is "dead quite".