[GreenKeys] 120VDC power supply noise?

[KC0NNC at aol.com]

Well, ehertz now that you have mentioned a second winding that goes  strictly 
to the ac capacitor, I now am 99.9% sure that is a sola connection and  
circuit, and I am reasonably sure what you have is a loose lamination in the  power 
transformer.  and yes, you could sub another transformer for the one  making 
the noise.  but unless you used the exact transformer, you would  loose the 
"sola" effect.
 
i would suggest you wrap the transformer with scotch 88 electrical tape,  and 
see if that helps, as well as perhaps sound isolating it with fiber board,  
or Styrofoam  or place the whole power supply into a box filled with  Styrofoam 
packing popcorn (unless it dissipates a lot of heat)  or take the  
transformer to a motor winding shop, and ask them to "dip it and pot it, and  bake it"  
The end laminations were quite prone to loosening up over time as  the shellac 
got crisp.
 
At 80 milliamps, I would suggest a 7.5 watt refridge interior lamp for a  
load, and see what happens if you wish to test run the supply loaded.
 
i always was adventuresome, and at one time did not have a loop supply  
readily handy, so I took 220 vac and full wave bridge rectified it, and all of a  
sudden had plus and minus a hundred or so volts referenced to earth ground, and 
 it was balanced as well.  and i placed I think 2 uf (oil or paper) in  
series with each input leg, to act as coupling from the ac mains, and did the  
normal LC filtering in the supply output legs, and had quite a respectable loop  
supply.  (obviously referenced to earth ground, so don't stand in a puddle  
barefoot while experimenting) but i figured all my equipment was seeing earth  
ground any way.  I never had anything short to ground, but had something  
shorted out, the 2 uf caps would have limited the fault current to an amp or so,  
and no damage would have come to the equipment.
 
I did notice that some of the tube demods I was using, sometimes had no  
polar relays in them, and switched the positive loop supply to ground (via the  
vacuum tube) anyway, and in this case, you were forced to use the positive side  
of the bridge anyway, but in case you needed the extra boost for a longer 
run,  you could always use the extended negative to drive a polar relay at the 
other  end, as Don mentioned.
 
73's for now
 
If I run into any of those loop supplies identical to the one you are  
working with, I will let you know and/or send them to you, I believe I have some  in 
storage somewhere.  I just could not bring myself up to tossing  them.
Harvey E.  Smith, KC0NNC
2020 Baculite Mesa Road
Pueblo, CO., 81001-2456

719  406 9735, 719 671 2671, 719 546  1418

zzzz/ryry