For what it's worth, with most old SS gear, I start at 50~60V on the line, wait an hour or more, then ramp up 10V, wait an hour or more, etc., until I reach 120V or trouble ensues. Always bring up the variac through the first few volts very slowly while watching the ammeter. If there's a short, this is when you will learn about it in most cases. As mentioned above, there are a few cases where the equipment normally exhibits bad behavior at low line voltage.