[GreenKeys] Another idea for a loop supply transformer

[Ken Schwieker]

When building a ST-6 many years ago I used a transformer that had a 
dual primary for 115 or 230 volt operation. The secondaries were used 
for the low voltage and the second primary as a loop supply winding. 
The total loads of the low voltage secondary and the new HV secondary 
were checked to be sure they totaled less than half of the total 
wattage that the transformer was rated for to prevent overloading of 
the primary.  Any sufficiently rated transformer can be used the same 
way for a loop supply.

The transformer used in my ST-6 is a Stancor P-6377. It has two 12 
volt  2 amp secondary windings as well as the two 115 volt primary 
ones. It made for a fairly compact ST-6. A link to a picture is 
below. The outside transformer shell was lifted off of another 
transformer for protection.

http://www.mindspring.com/~ksweek/images/ST-6.jpg

This or any other suitable transformer could have been used alone 
with the two secondaries wired to buck either the input or the output 
to give a somewhat lower output voltage if desired.