Need help on how to use a variac.

I just bought a variac and will use it to bring back some old equipments. I need your advise on the following questions:
What is the starting voltage?
What are the incrementals?
How long I need to run for each voltage setting?
Thank you very much.
This is one I've found on the internet:

I have a few books at home dealing with this with guitar amps.

Hope this helps.
That link gives a way to bring up the amp to see if it is functional, but it is way to fast if the object is to reform the dielectric on the caps.
Thank you for the info!
If you're talking about old tube gear, here's a tip. I recommend you use a current meter, the same size as the variac is rated (ie: 5 amps). After you've tested the tubes and checked that they're all in the right sockets, and the fuse is the right size, terminate the output with a 10 ohm 10 watt resistor. A simple rule of thumb is to bring it up to 50%, or 60 volts. If you don't see excessive current draw, right away or after 10-20 seconds or so, you're doing well. Let it sit there for a time (say 1/2 hr.) to reform the electrolytic capacitors. Then slowly swing up to operating voltage. Again, watch for excess draw on your meter. It will "bump" a bit as you crank it up, but should settle. Now it's time for the smell test. If it doesn't smell like a toy train that's run too long, or you don't see an orange glow on the output tube plates, you're in the ball park. Next, try a live test, with a durable speaker.