Variac question...

I didn't want to send this to the TC mailing list b/c it is pretty simple.
If you
have time...

I picked up a variac at the swap meet for $10.  It is an old, but
unused, Powerstat rated at 1.3 Max KVA and 9.0 Max Amps.  My 12/60 NST
requires 6.35 amps with the secondary shorted.  With 2 of these I will
be at 1.53 KVA and 12.7 amps.  Clearly this is over the label value but
hopefully under the true design value (without safety factor).  What
kills Variacs?  I assume that it is heat, if that is the problem I will
fan cool.  Do you think that this variac will make it???  Any
suggestions, other than look for bigger variacs :-)