A variac is a brand name for a "variable isolation transformer". I borrowed one from a friend last weekend. It was
like this one.
They allow you to bring the power up very slowly. This will sometimes "re-form" the electrolytic capacitors, and save you having to replace them (some will say replace them anyway, probably good advice). It also sometimes lets you find shorted parts without burning up any unobtainable parts.
A dim-bulb tester is the cheap way. You just get a bulb socket, a plug, and an outlet. Wire this up so the bulb will be *in series* with the radio. You screw in higher wattage bulbs to raise the voltage. This way works fine.
If by driver you mean speaker, youll want to salvage the old one if you can. It's probably "electrodynamic", meaning that it has an electromagnet for the speaker magnet. This electromagnet usually doubles as the choke for the power supply. The radio wont work without it. Maybe if it is bad it can be fixed.
If it can't be fixed, there are other ways. You could add a choke coil. Or, you could replace the choke coil with a resistor (that was done a lot in the old days, but to really be right some other component values would have to change).
What I have done in the past is mount the old speaker elsewhere in the cabinet, with the voice coil disconnected. then you can mount a regular speaker. That way the old one is still there if is becomes feasible in the future to repair it.
Oh, and by the way the "41" in the model number means 1941.
Have fun!
John