Electronics experts - look in. How does a 'variac' actually work? and how does it differ from a multi-tapped?

Question

transformer?

I'm looking to power-up a rebuilt 1950's vintage television set, but it still has many of it original components which I don't want to 'shock' with a full mains power switch-on.

I know that it is commonly recommended practice to bring up the power slowly, over a number of hours, by using a variac. I don't have one, and they're an expensive item.

Can I use an array of step-down transformers instead? Offering voltage steps of 25v or 50v. Would these steps be small enough, or have I misunderstood how the variac does its job?

In short, does a variac actually, simply, control voltage via dial selected taps? or does it (electronically) 'pulse' the full mains voltage in a variable 'mark-to-space' ratio?

Genuine answers only please!

Answer 1

I would be careful using a light dimmer for this purpose. A light dimmer chops the sine wave and may damage the unit. The main component that you need to worry about in old electronics is electrolytic capacitors. If you go through and give them a gentle charge with voltage source and a resistor, and check them out, you should be OK to power on the unit. Old tube set are pretty tough as long as non of the capacitors are not shorted so if you check the capacitors first, you don't much risk of damage.

Answer 2

Grey:

Yes, the old variac operates just as you stated by dial selected taps using a wiper that travels across the taps.  Why don't you just buy a light dimmer and use it like a variac.  It should handle the current demand OK.  Select one that has the highest current current rating you can find.  Your TV probably runs 350 watts.  A light dimmer should be just fine if the power supply can handle the chopped AC.  That old stuff was tough.  Should be OK.

Good luck and have fun.  -  73 from the Fisherman