Is it possible to build a Variac without using Transformers?

[rickselectricalprojects]

I brought a "scr dimmer" of ebay and it could apparently vary ac voltage from 10-240 v ac. I don't remember how i wired it up but i Ballested it with two heaters and put a resistive load (a lightbulb). I did get a output voltage of 10-240v but it DID NOT have a normal sinewave. The only thing that was good for was blowing up speakers and it still was very bad at that. So the best bet would be to go and pick up a cheap and/or used variac of ebay

[Richard Crowley]

I did get a output voltage of 10-240v ....

No, you didn't really.  You got the 240 VAC RMS sine wave chopped up to vary the average power to the resistive load with a good amount of "averaging" in the thermal mass of the incandescent lamp filament.

[Refrigerator]

Well, if you put 350 diodes across your 240V_AC you can use the diode voltage drop to chop the voltage up...

[madires]

I did get a output voltage of 10-240v ....

No, you didn't really.  You got the 240 VAC RMS sine wave chopped up to vary the average power to the resistive load with a good amount of "averaging" in the thermal mass of the incandescent lamp filament.

Some references including nice pictures and graphs:
- http://www.ilight.co.uk/downloads/iLIGHT%20Binder-HowDimmers.pdf
- http://home.howstuffworks.com/dimmer-switch.htm
- https://en.wikipedia.org/wiki/Dimmer