On Feb 4, 9:01 pm, "willismat" wrote:
I have a preamp which came with a wall wart causing hum. Doing
research into past posts here brought a comparison between RS wall
warts back in 1998, saying that catalog # 273-1662 was unregulated and
caused hum while #273-1664 was regulated and did not. Having just
checked RS's website, 273-1664 is no longer available, but 273-1662 is
listed as being regulated (perhaps upgraded over time?).
The power requirement of my preamp is 12 to 13.8 VDC @ 100mA. RS
carries 3 regulated warts which would cover that:

273-1680 3-12 VDC @ 1000mA

273-1662 1.5-12 VDC @ 300 mA

273-1667 3-12 VDC @ 800 mA

Which one would be the best choice to see if I get any improvement?

I can't tell you which if any of the units you list will be suitable.
I have found great variability amoung units with the same part number.

One thing that might help is to take a portable SW, I use a DX398
becuase
I have one, and power up each of the units and see if any are RF
quiet.

Regulation is one aspect, but modern diodes turn off so fast that they
can cause serious RF noise.

This is one viewpoint.
http://home.computer.net/~pritch/shortwav.htm

I only use wall warts operation away from home or for those odd
devices
that don't operate from +12V. I tend to build LM317 step down
regulators
to allow +3V, +6V or +9V devices to operate from my 12V rail.

Some devices require AC and some are positve ground. I try to avoid
the
later if at all possible.

Good luck.

Terry