Tom,

Usually the transformer vibration gets transferred to the cover, and 
that is what you hear.    There are 3 screws across the top rear, and 4 
more next to each of the rubber feet.   The cover kind of wraps around, 
so these screws are on the bottom.  Try tightening them a bit.

Some people will take a piece of index card or something and jam it 
between the cover and the front panel to try and dampen  it a bit. 
Either at the top, or one of the sides where  cover and front panel 
meet.   Or lay a brick on top of the cover.

73, Steve KW3A

On 12/11/2015 10:15 PM, Tom Behler wrote:
> Steve:
>
> I'm sure the hum is simply mechanical.  I'm also quite positive that the hum
> is not due to anything like bad filter caps or poor voltage regulation.The
> supply seems very stable in those regards, after a number of dummy load
> tests I did earlier this evening.  I also had a 40-meter CW qso with an
> experienced CW operator from Kansas who said that my tone was extremely
> clear and clean.
>
> May try the foam rubber approach, although, as you say, I'm going to have to
> be careful that I don't block adequate air circulation.
>
> Other than this, I don't think I'll do anything inside the supply
> itself--not worth the trouble and the risk of voiding the one-year warranty.
>
> Tom Behler: KB8TYJ
>
>
>
>
>
>
> -----Original Message-----
> From: For blind ham radio operators [mailto:[log in to unmask]]
> On Behalf Of Steve Dresser
> Sent: Friday, December 11, 2015 9:59 PM
> To: [log in to unmask]
> Subject: Re: Question on New RS35 Metered Power Supply
>
> Tom,
>
> I'm pretty sure that the hum is mechanical, caused by vibrations of the
> transformer inside the supply being amplified by the metal case.  You might
> try placing the supply on a thick piece of foam, keeping in mind that you
> don't want the four feet to sink too deeply into the foam, which would block
> circulation and probably give you a problem that would make you long for the
> good old days when you were being annoyed by the hum.  I suppose you could
> open the supply up and try to isolate the transformer from the case, but
> that sounds like a lot of work, and I don't think you'll get much for your
> efforts.  Bottom line: don't worry about the hum as long as it's not the
> result of bad filter caps or poor voltage regulation (and from what you've
> said, I don't think it is).
>
> Steve
>
> ----- Original Message -----
> From: "Tom Behler" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: December 11, 2015 20:45
> Subject: Question on New RS35 Metered Power Supply
>
>
>> Hi, everyone.
>>
>>
>>
>> Well, I got my new Astron RS35 metered linear power supply yesterday, and
>> set it up tonight here in my home shack.
>>
>>
>>
>> Everything seems to work well, in that I get the output power readings I
>> would expect on resonant HF frequencies via my TS590, and on VHF/UHF
>> frequencies via my TMV71A.
>>
>>
>>
>> I have noticed something, though, that I could use some input on.
>>
>>
>>
>> For some reason, this new RS35 has a bit of a louder hum than I noticed
>> with
>> my older unit.
>>
>>
>>
>> Has anyone noticed this sort of thing with the newer RS35's, and if so,
>> were
>> you able to do anything to address the issue?
>>
>>
>>
>> I might consider moving the supply to another location, because right now,
>> it is on a shelf just above my operating position.  However, I will need
>> to
>> be certain that the newer location gives the supply sufficient space for
>> ventilation.
>>
>>
>>
>> I am not sure the problem is significant enough to return it to HRO, but I
>> would be curious if anyone has had a similar experience, at least
>> recently.
>>
>>
>>
>> Tom Behler: KB8TYJ
>>
>>
>