Tom,
Any increase in output power will cause the hum level to increase - 
perhaps your transformer and cabinet are particularly sensitive to 
this.  A lifetime ago I used the sound of the power transformer of my 
Johnson Viking Valliant to resonate the final power 
amplifier.  Knowing the sound I wanted to hear I could put that puppy 
right on the money.  Used to amuse my young ham friends!  But with a 
case of beer behind us, we were easily amused!
You should be fine.
Pat, K9JAUAt 02:01 PM 12/12/2015, you wrote:
>Hello, again, everyone.
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>
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>I am now beginning to wonder if today is my day for Murphy to make a visit
>here, or just what exactly the deal is.
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>I was working a bit of the 10-meter contest today, and noticed a further
>problem with the hum issue on my new Astron RS35 power supply.
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>I'm not sure why I didn't notice it last night when I did my testing, but
>now, I find that whenever I transmit in CW at any power level-i.e. 5 watts
>or 100 watts, the hum on the RS35 slightly increases.  In other words, when
>I key down, I hear a slight, but noticeable increase in the hum at any power
>level.
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>So, now, I'm trying to decide whether I actually should return the supply to
>H R O.
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>I have my receipt and all other documentation, but I'm wondering whether the
>folks at HRO would see this as a significant enough of a problem for a
>product return.
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>The supply still seems to carry the load ok, and does put out what I would
>expect in terms of output power readings, but the hum issue is a noticeable
>one now, on several counts.
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>I don't mean to be obsessive about this, but I wouldn't expect to be dealing
>with this sort of issue with a newly-purchased power supply like this.
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>I'd continue to be interested in anyone's thoughts.
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>
>Tom Behler: KB8TYJ
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