Chris Lewis wrote:
According to M Q :


In 1963 my family moved into a (new) house that had a dimmer
switch for the dining room ceiling light. While it was about
the same size as today's dimmers, it was not today's 4 component
circuit. I remember looking at the schematic. There were a dozen
or more components, including a transformer. I didn't know
enough then to understand the circuit, so I can't offer more details.


The classic "basic" dimmer circuit published back in the late 60's and
earlier consisted of a SCR (later triac), a diac (looks like
an ordinary semiconductor small-signal diode, and my rusty
memory seems to indicate it's shown in schematics as two
paralleled back-to-back zener diodes), rheostat (variable resistor
with the knob ;-) and another resistor or two. The other components
you saw (including the transformer) were probably noise filtering
which is considered an "optional add-on".

More modern circuits do with less (or no) noise filtering, and
use a resistive network instead of a diac to trigger the triac
IIRC. SCR-based dimmers need a lot of filtering, and triac-based
dimmers need less - since modern circuits don't use SCRs, the
need for noise filtering is less.
Hmmm,
Remember first ever popular transistor RCA CK722 PNP Ge junction
type? When I got one of them at such a high price and built a small
receiver with it, what an excitement. Was back in the '50s. Now I am
using florescent lights and dimmers in the house. Waiting for LED lights
to become cheap in price.
Tony, VE6CGX