[R-390] How to repair your Variac

[2002tii]

Bill wrote:

>If the winding can get hot, because it isn't fused, then don't depend on
>solder to hold the splice together. Make a mechanical connection first.

I take it as a given (other than when breadboarding with the "ugly 
ground plane" method) that soldered joints must be mechanically 
secure before soldering.  That said, if the variac gets hot enough 
that the integrity of a solder joint is compromised, pray that the 
fire brigade is already on the way.

>Use some transformer paper to keep the splice from rubbing on the
>insulated turns of wire.

That is a useful precaution if you lay the splice down on the 
windings.  I didn't -- instead, I made a twisted "pigtail" 
connection, soldered it, and left it sticking up away from the 
windings to avoid any more bending of the wire than necessary (which 
work-hardens the wire and makes it more susceptible to breakage).

If you want, you can mechanically stabilize the new portion of the 
winding by applying transformer varnish or lacquer (leaving the brush 
path clear, of course).

Best regards,

Don