Adjustable AC Supply?

[Paul Marossy]

I have built an adjustable power supply using a LM317 regulator, which works fine for DC power. But, lately, I have found myself wanting to have a variable AC power supply, ranging from about 6-13V. Is there a way I can do that? Is it a simple as having a transformer in a box with a rheostat in series with the secondary?

[Nasse]

When I was a kid they bought me nice Märklin model railway. I think they used to have such transformer in the old days. The secondary was made of bare wire, and there was plastic insulated rotary knob on top of it, a sliding contact moved on top of transformer coil, you could adjust the ac  voltage... I still have the transformer in a junkbox (without the case, I made a fuzzbox or something of it) but the slider I have lost. Don´t know how they are done nowadays.

[R.G.]

Do a search on "variac".

[Paul Marossy]

Yeah, I guess a variac is what I need, huh? I was thinking that those were for 110V operation, but I guess that could be adapted to lower voltages, couldn't it?

Thanks.  

[Fret Wire]

I have a Staco variac that adjusts from 0 - 140v, 5A, .7KVA. It's got a govt. stamp and sticker on it. No meter, just the graduated dial, on/off toggle, LED, Fuse reset, and 3-prong output receptacle. Not the usual round looking ones, 7 1/12"H x 5 1/2"W x 5 1/2"D, with a carrying handle.

Funny, measured voltages are about 2v higher than the dial settings. My guess is that being older, it was designed/calibrated for 117v.

You can usually find good variac deals on Ebay all the time.

[Lonestarjohnny]

Paul, I've got some spare Variac's if you need 1,
JD

[Paul Perry (Frostwave)]

Suppose you want 6v AC to 12v AC, just get a variac, and plug a 12v AC tranny into the output. Now, as the variac goes from 0 to 110 (or 0 to 230 here in Australia) the outpuit of the tranny is 0 to 12.
In a CSIRO lab I saw a big variac running a two-bar radiator :shock:  

[sir_modulus]

Paul has a good idea. Model train regs are good too(usually 0-13V AC). You could also build (like me) a super power supply. Just make a adjustable regulated heavily filtered DC supply, and put it through an inverter.