Garth, I'm no expert, by any means, but have dabbled in old stuff for quite a few years. I am always concerned that even at the first application of voltage, something might be actually shorted, and not just needing "reforming". Good idea if one can devise some way to measure, even roughly, how much current is being drawn from the Variac.
Some (me included) have inserted a low wattage incandescent lamp in series with the applied voltage. Better, probably would be an AC ammeter. Of course one never knows just what current is normal, but a nearly dead short should be reasonably easy to detect.
Start off very slowly, feeling (without touching) around for warmer than normal parts, keeping nose carefully tuned for any odors not present when the stinking thing was still cold and unpowered.
Keep fire extinguisher and telephone handy. Good Luck!

Old Chief Lynn, W7LTQ
"gareth" wrote in message ...
Having now borrowed my friend's Variac, what is seen as
good practice for ramping up old valve radios to reform the
capacitors?

Start off at, say, 50VAC and then increase by 50VAC every
1/2 hour until 240V is reached?