probably the fan.
that's about all that can make any noise inside a switching power supply.
The bigger supplies will have a fan that comes on automatically when allot
of current is being drawn.
73
Colin, V A6BKX
----- Original Message ----- 
From: "T Behler" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, December 26, 2007 6:48 PM
Subject: using TS480 with 35-amp Samlex switching power supply


> Hi, all.
>
> I have noticed something when using my TS480 with my 35-amp Samlex
switching
> power supply.
>
> When I transmit with 100 watts, in CW mode or in RTTY mode using the stock
> mic, I notice a slight but audible hum coming from the switching power
> supply.  The hum stops when I stop transmitting.  I had my XYL take a look
> at the meters on the front of the supply, and they say I'm running at 13.8
> volts, and drawing about 19 amps, which is about what I'd expect.
>
> And, just for the record, I'm doing this with a resonant antenna, and just
> using the auto-tuner to be sure I have a perfect match.
>
> Is this slight but noticeable hum when transmitting normal?
>
> Thanks, and 73 from Tom Behler:  KB8TYJ
>
>
>
> -- 
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>