[Hallicrafters] tech question please!

[Nash4447 at cs.com]

Gotta question for the technical experts ...

I noticed that the modern "switching" power supplies are able to develop 
quite a bit of current in a very small package.   I found one of these units that 
puts out 6 volts regulated at about 15 amps. The reason I bought the thing was 
that I wanted a supply to run mobile tube radios on my bench. Well, I hooked 
the supply up to my tube radio and it handled the current load beautifully 
without even getting hot ( 7 amp load), BUT the damned thing creates so much hash 
that I can't hear anything through the radio. 

Does anyone have any good ideas how I might be able to eliminate the hash? I 
haywired things up just to try it out. The exposed supply was sitting next to 
the receiver.  Do these supplies have to be in a metal box for shielding ?  
Would some sort of RF choke arrangement in the output lead help?
Or are switching type supplies just not suitable for my purpose?

Glenn K6PZT