What technology changed

[DPittman]

I was given this "new" unused rheostat/potentiometer. What's the reason for the massive size difference between the old and the new?

I'm now going to go search to make sure that a rheostat and potentiometer are the same things as I assumed in the above statement...

 

[SparWeb]

They are not equivalent devices.

That is an awesome rheostat you have there. Take good care of it!
I think that's also called a "variac" but maybe someone more knowledgeable needs to correct me.
The wiper bar on the top is covering the "output" spec but I assume it can vary from 0-120VAC output, based on the 2.2A current rating and 270VAC power rating.
If you don't want it, I have a use for it.

The other thing is a cheap potentiometer made in China. Variable resistor. Useful but not very special.

 

[DPittman]

They are not equivalent devices.

That is an awesome rheostat you have there. Take good care of it!
I think that's also called a "variac" but maybe someone more knowledgeable needs to correct me.
The wiper bar on the top is covering the "output" spec but I assume it can vary from 0-120VAC output, based on the 2.2A current rating and 270VAC power rating.
If you don't want it, I have a use for it.

The other thing is a cheap potentiometer made in China. Variable resistor. Useful but not very special.

Ah yes my preliminary research indicated right of the bat that they are not the same thing. I just haven't quite figured out yet what application the old rheostat was made for. I just knew that someone on this forum would know these things. I will continue to read.

 

[VicHobbyGuy]

A Variac isn't the same as a rheostat; it's a transformer and a rheostat is a variable resistor. The windings on a Variac are copper wire; it's a type of transformer and the wiper is selecting differing numbers of turns on one of the windings. A wire-wound rheostat winding is made of resistance wire. BTW, depending on how you connect them, most Variacs will output voltages from zero to a voltage greater than the input, IME.

 

[Susquatch]

Yes, a variac is a variable transformer and a rheostat is a variable resistor.

Think of the Variac as a very efficient variable voltage AC power supply. That supply can also be rectified and filtered to easily become a variable voltage DC power supply.

I had a nice one around here someplace but it has disappeared.......