[R-390] Isolation Transformer

[Drew Papanek]

On the subject of isolation transformers Gary E Kaufman wrote:

"You can grab most any 2 large filament transformer with the appropriate
   wattage ratings and put them back-to-back.  I used a pair of 56v/3A
   transformers for many years set up as 115:56<--->56:115 with good success
   while repairing AC/DC tube radios.  There was about a 5% voltage drop 
over
   line voltage.

           Admittedly this may be tough if you really need a 750-1000 watt 
unit."

Transformers from junk microwave ovens can also be used in this manner by 
connecting the HV windings together.  One end has a terminal, the other is 
usually internally connected to the transformer's frame.  Connect frame to 
frame, HV terminal to HV terminal.   HV runs a couple or few KV; make sure 
that connection is well insulated and done with appropriate wire (salvage 
that from the junk microwave also).

These transformers will handle quite a bit of power and you can use 2 
differing units to get a slight increase or reduction in net voltage.

Time to don your dumpster diving duds!

Drew

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