[Elecraft] Power Supply Hummmm

[George, W5YR]

Well, they are quite variable in acoustic output, in my experience. My
little RS-20M is almost silent at all times.  My VS-35M (used to run
the PROs) when switched on (no load) may come up almost silently or
may roar like a lion. Since it is always turned on under the same
load - zero - all I can figure is that something is sensitive to the
phase of the line voltage at the instant the switch turns on. Makes no
sense, but what else? Any ideas?

The thing is so heavy that I haven't taken it down for a general
tightening up, but that may be next.

One other thing: even though the supply might make little or no
audible noise, I found that having it on the operating desk with the
Heil GoldLine mic on a stand caused an unacceptable hum content in the
mic output from direct vibration pickup. So, I mount all power
supplies on a separate table/stand and have a pad of dense foam rubber
under them. Seems to hold the hum/rattles down a lot.

73/72, George
Amateur Radio W5YR -  the Yellow Rose of Texas
In the 57th year and it just keeps getting better!
Fairview, TX 30 mi NE of Dallas in Collin county EM13qe
K2 #489  IC-765 #2349 IC-756 PRO  #2121 IC-756 PRO2 #03235

----- Original Message -----
From: "Ron D'Eau Claire" <rondec@easystreet.com>
To: "'Elecraft'" <elecraft@mailman.qth.net>
Sent: Saturday, December 21, 2002 1:08 PM
Subject: [Elecraft] Power Supply Hummmm


> 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".