[AMRadio] Cheater cords and isolation transformers


D. Chester k4kyv at charter.net
Sat Nov 17 11:34:10 EST 2007


Before I retired, at the high school where I taught they decided to clean 
out the electronics lab that had set unused for over 10 years, because they 
needed the space.  Most of the stuff was to go to the dumpster, but luckily 
my classes were in the same building, so I found out about it almost 
immediately.  I pulled a load out of the dumpster and then helped myself to 
any of the rest of the "junk" that I wanted, that had been piled up in the 
middle of the room awaiting disposal. I brought home several boxes of 
carbon resistors and capacitors,  about a half dozen variacs, a bunch of 
small hardware, some Millen GDO's, some chep GDO's, and much more.  The 
custodian of the building was glad to see me haul it away because I saved 
her a lot of back-breaking work.  I made at least 3 trips home with the car 
stuffed full.

Amongst the best goodies of all were about a half dozen RCA TV isolation 
transformers, designed for use in a  service shop.  Rated at 400 VA, they 
have a switch to select your mains voltage, with taps every 5 volts from 105 
volts to130 volts.  There are 6 outlet recepticals mounted on the top of the 
case, one set of 3 marked "direct" which are connected to the 105, 115 and 
130v taps on the primary, marked "low" "medium" and "high".  Three more, 
marked "isolated" have identical voltage outputs connected to a separate 
secondary winding.

I gave one away, but I'm now using the rest all over the place.  They make 
good line voltage adjusters with the tapped switch.  They isolate the a.c. 
line and cut down on hum and ground loop problems, and may also provide some 
degree of surge protection, since in case of a high amplitude lightning 
surge the core should saturate and limit the peak output voltage from the 
isolated winding.  I use a couple in my ham station and have one in the 
house to run all the TV and stereo equipment.  One is on the workbench, 
where the variable voltage feature allows me to run my soldering iron at low 
enough voltage that the tinning doesn't burn off from the tip, and the tip 
doesn't self-destruct if I forget and leave the iron on overnight. No 
accoustical hum, and the transformers barely rise in temperature even after 
being plugged in indefinitely.

These would be ideal for running ac/dc radios.

Don k4kyv 



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