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Posted by Tony Hwang on November 8, 2007, 1:24 am
Chris Lewis wrote:
>
>>Chris Lewis wrote:
>>
>>>
>>>>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.
Hmmm,
You ought know then vacuum tube version of SCR, the Thyristor!
Also include Diac as well on solid state side.
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