According to lee h :
Chris Lewis wrote:
According to lee h :
franz frippl wrote:

Dimmer switches are no more than rheostats. If carbon were to build
up on part of the switch, it may be sufficient to affect voltage.
Might cause a voltage drop.

You could test this with a volt/ohm meter.

In ye olde days, you were right. However for many years,
the triac-based dimmer switch has been the more common.

"More common"? Even in ye olde days, rheostat dimmers were extremely
rare, and they're now essentially non-existant.

Chris, I suspect that your definition of 'ye olde' and 'many years'
is more short term than mine.

Probably not. I'm older than I look ;-)

In junior high school we had an electronics lab that a couple of us
spent time in. We did some stuff with SCRs. Triacs weren't available
then I don't think.

Actually, most of what we did was with vacuum tubes. I built a
radio telescope out of a vacuum tube IF strip out of a 50's B&W
TV set and used an oscilloscope to display the results. 150'
baseline on the antennas allowed me to do interferometry work.

Worked pretty good ;-)

The SCR which enabled solid-state
control of dimmers was not invented until the late fifties. Rheostat
dimmers and auto transformers (Variacs) were the *only* means of
dimming lights until then.

Not quite, but we'll take that as a given.

So they were hardly rare.

How many houses had any dimming whatsoever prior to SCR/triac dimmers?
How many houses had more than one? How many of these were used
in general purpose things rather than very specific (and usually
low wattage) fixtures?

I would submit that up until the late 60's, general purpose dimming
circuits were almost non-existant in residences. What dimming
circuits there were were expensive heavy-duty industrial units,
or low wattage (usually considerably less than 50W), often a part
of the fixture itself, or the cabinet it was installed in.

Solid state
dimmers were not commonly used in homes until the late
sixties. But, you are right about the rheostat dimmer's heat
output. Most were mounted in a box on the outside surface of
a wall, not in a switchbox.

And variacs are much larger & heavier. Saw a brand new one a few
days ago. 600W IIRC. It weighed about 25 pounds, and was bigger than
a regular two slice toaster. $200 IIRC. Hadn't seen one in a
very long time.

I don't think too many people had those in their house to dim
the mood lights.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.