[R-390] line voltage reducing question

[Charles P. Steinmetz]

W. Li wrote:

>I use a 5A metered Variac. By having a transformer-type line 
>coniditioner, and a computer-type AC switch selector, each of my 
>three receivers can be easily powered up individually.

One thing about variac-type autoformers:  Most 120 volt units come 
from the factory wired for 120 in and 0-140 out.  This creates the 
possibility that the accidental nudge of an elbow could readjust it 
for an overvoltage condition rather than the intended undervoltage 
operation.  They can easily be re-wired internally for 0-120 
operation, in which case it is not possible to have a voltage output 
higher than your line input.  For powering BAs, this can be a 
worthwhile modification.

With the General Radio-type variacs, it is a simple task of moving a 
wire from one screw terminal to another.  With the "powerstat"-type 
units (Superior/Staco and others), it generally requires unsoldering 
a wire from one location on the winding and soldering it to another location.

Some of them even have a 0-120 scale printed on the flip side of the 
0-140 scale.

Best regards,

Charles