Anybody remember the name of the ancient dimmer that used a variable
inductor in series with the lighting circuit?

The chorus that I sing with is performing in a turn of the last century
theatre. I was marvelling at the ancient stage technology. They still have
the old style sandbag counterweights and belaying pins to anchor the lines
though the lines themselves have been changed from the original hemp lines
(guess they were all smoked by now...) to new black cotton lines that
conform to newer codes. The original lighting panel has long since been
replaced by a new digital board but I was talking with the theatre manager
and trying to remember some of the old names.

Rheostats, the original dimmer technology were replaced by the variable
inductor types to some extent. All of these were eventually replaced by
Variac types for many years until the newer electronic dimmers took hold.
I have fond memories of high school stage crew, running the Variac dimmer
board. On scene changes, the dimmers could be mechanically ganged into a
master group and master groups could be ganged to the grand master.
Sometimes it took two people to pull the grand master - and it had a 4 foot
handle. Oh, to have had a DMX back then.

Oppie
www.chordsmen.org

Oppie wrote:

Anybody remember the name of the ancient dimmer that used a variable
inductor in series with the lighting circuit?

A saturable reactor ? A TO-3 device feeding current into a choke ?

Graham

Oppie wrote:

I have fond memories of high school stage crew, running the Variac dimmer
board. On scene changes, the dimmers could be mechanically ganged into a
master group and master groups could be ganged to the grand master.
Sometimes it took two people to pull the grand master - and it had a 4 foot
handle.

Only about a 2 foot handle here and that was in 1970 with a quite new rheostat
dimmer panel.

Graham

"Oppie" wrote in message
...
I have fond memories of high school stage crew, running the Variac dimmer
board.

Our control panel had a bunch of rheostats that fed DC (?) control voltages to
a large "dimmer rack" (which was in an adjacenet room with good-sized concrete
walls... there was probably the potential for 50kW flowing through that
room...). The dimmer rack had these slide-in dimmers (in two sizes... most
were something like 1kW, and some double-size units were either 2 or 4kW),
which in retrospect I figure were TRIAC-based, performing phase-angle control.

For curtains, etc., we had "carriages" that traveled up and down a pair of
rails, and you stacked standard weights onto the carriage to create the
appropriate counterbalance (the weights were either the same or very similar
to the ones you see on exercise weight machines) - no sand bags.

It's probably been converted to DMX as well by now. (Ironically, Electronic
Theatre Controls was only a few miles away from the school -- I went dumpster
diving there a couple of times. Too bad they went out of business...)

On Thu, 19 Apr 2007 12:00:34 -0400, "Oppie"
wrote:

Anybody remember the name of the ancient dimmer that used a variable
inductor in series with the lighting circuit?

The chorus that I sing with is performing in a turn of the last century
theatre. I was marvelling at the ancient stage technology. They still have
the old style sandbag counterweights and belaying pins to anchor the lines
though the lines themselves have been changed from the original hemp lines
(guess they were all smoked by now...) to new black cotton lines that
conform to newer codes. The original lighting panel has long since been
replaced by a new digital board but I was talking with the theatre manager
and trying to remember some of the old names.

Rheostats, the original dimmer technology were replaced by the variable
inductor types to some extent. All of these were eventually replaced by
Variac types for many years until the newer electronic dimmers took hold.
I have fond memories of high school stage crew, running the Variac dimmer
board. On scene changes, the dimmers could be mechanically ganged into a
master group and master groups could be ganged to the grand master.
Sometimes it took two people to pull the grand master - and it had a 4 foot
handle. Oh, to have had a DMX back then.

Oppie
www.chordsmen.org


As I recall, the saturable reactor was a transformer with two
windings. One of the windings was in series with the input power to
the lights. The other winding was provided with a variable DC power.
When there was no DC present, the other winding was high impedance to
the lamp loads. When the DC was applied the core in the transformer
was saturated and the impedance went down as the lights came up!

John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"
t

On Thu, 19 Apr 2007 12:00:34 -0400, "Oppie"
wrote:

Anybody remember the name of the ancient dimmer that used a variable
inductor in series with the lighting circuit?

The chorus that I sing with is performing in a turn of the last century
theatre. I was marvelling at the ancient stage technology. They still have
the old style sandbag counterweights and belaying pins to anchor the lines
though the lines themselves have been changed from the original hemp lines
(guess they were all smoked by now...) to new black cotton lines that
conform to newer codes. The original lighting panel has long since been
replaced by a new digital board but I was talking with the theatre manager
and trying to remember some of the old names.

Rheostats, the original dimmer technology were replaced by the variable
inductor types to some extent. All of these were eventually replaced by
Variac types for many years until the newer electronic dimmers took hold.
I have fond memories of high school stage crew, running the Variac dimmer
board. On scene changes, the dimmers could be mechanically ganged into a
master group and master groups could be ganged to the grand master.
Sometimes it took two people to pull the grand master - and it had a 4 foot
handle. Oh, to have had a DMX back then.

Oppie
www.chordsmen.org


Most of the theatres that I have been in used Variacs to control
lighting. A variac is an autotransformer, allowing variable voltage
output with the turn of a dial.

"Oppie" wrote in message
...

Anybody remember the name of the ancient dimmer that used a variable
inductor in series with the lighting circuit?

"Magnetic Amplifier".

On Thu, 19 Apr 2007 14:57:24 -0400, PeterD wrote:

On Thu, 19 Apr 2007 12:00:34 -0400, "Oppie"
wrote:

Anybody remember the name of the ancient dimmer that used a variable
inductor in series with the lighting circuit?

The chorus that I sing with is performing in a turn of the last century
theatre. I was marvelling at the ancient stage technology. They still have
the old style sandbag counterweights and belaying pins to anchor the lines
though the lines themselves have been changed from the original hemp lines
(guess they were all smoked by now...) to new black cotton lines that
conform to newer codes. The original lighting panel has long since been
replaced by a new digital board but I was talking with the theatre manager
and trying to remember some of the old names.

Rheostats, the original dimmer technology were replaced by the variable
inductor types to some extent. All of these were eventually replaced by
Variac types for many years until the newer electronic dimmers took hold.
I have fond memories of high school stage crew, running the Variac dimmer
board. On scene changes, the dimmers could be mechanically ganged into a
master group and master groups could be ganged to the grand master.
Sometimes it took two people to pull the grand master - and it had a 4 foot
handle. Oh, to have had a DMX back then.

Oppie
www.chordsmen.org


Most of the theatres that I have been in used Variacs to control
lighting. A variac is an autotransformer, allowing variable voltage
output with the turn of a dial.

I have been "backstage" for at least 40 years. Back then I recall
big-ass chokes with a moveable core to change the inductance.

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

America: Land of the Free, Because of the Brave

"John Ferrell" wrote in message
...
On Thu, 19 Apr 2007 12:00:34 -0400, "Oppie"
wrote:

Anybody remember the name of the ancient dimmer that used a variable
inductor in series with the lighting circuit?

The chorus that I sing with is performing in a turn of the last century
theatre. I was marvelling at the ancient stage technology. They still have
the old style sandbag counterweights and belaying pins to anchor the lines
though the lines themselves have been changed from the original hemp lines
(guess they were all smoked by now...) to new black cotton lines that
conform to newer codes. The original lighting panel has long since been
replaced by a new digital board but I was talking with the theatre manager
and trying to remember some of the old names.

Rheostats, the original dimmer technology were replaced by the variable
inductor types to some extent. All of these were eventually replaced by
Variac types for many years until the newer electronic dimmers took hold.
I have fond memories of high school stage crew, running the Variac dimmer
board. On scene changes, the dimmers could be mechanically ganged into a
master group and master groups could be ganged to the grand master.
Sometimes it took two people to pull the grand master - and it had a 4
foot
handle. Oh, to have had a DMX back then.

Oppie
www.chordsmen.org


As I recall, the saturable reactor was a transformer with two
windings. One of the windings was in series with the input power to
the lights. The other winding was provided with a variable DC power.
When there was no DC present, the other winding was high impedance to
the lamp loads. When the DC was applied the core in the transformer
was saturated and the impedance went down as the lights came up!

John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"
t

Saturable reactors used to be very common in TV E/W correction circuits, I
even recall a Relisys monitor that used one as a B+ regulator.

Eeyore wrote:


Oppie wrote:


Anybody remember the name of the ancient dimmer that used a variable
inductor in series with the lighting circuit?


A saturable reactor ? A TO-3 device feeding current into a choke ?

Graham

Check; saturable reactor.

"ian field" wrote in message
news
Saturable reactors used to be very common in TV E/W correction circuits, I
even recall a Relisys monitor that used one as a B+ regulator.

I worked on a variable speed sewage pump motor (50 HP) that used a mag amp
to control the speed. We had to interface it to a level control.

"Jim Thompson" wrote in
message ...

I have been "backstage" for at least 40 years. Back then I recall
big-ass chokes with a moveable core to change the inductance.

...Jim Thompson

Bingo - That's what I remember in one of the older stages I worked once.
Nothing to do with mag-amps or saturable cores. Now the question is if that
dimmer system had a trade name? I doubt that they called it a 'big-ass
choke..."

Every time I see a moveable core arc welder (to adjust welding current) I
think of that old and scary dimmer cage.

Regards,
Oppie

"PeterD" wrote in message
news
Most of the theatres that I have been in used Variacs to control
lighting. A variac is an autotransformer, allowing variable voltage
output with the turn of a dial.

The Variac was a trade name for an adjustable autotransformer. I haven't
seen a variac board in any theatre in the last 25 years. The cost of
electronic controls has come down so much that everybody converted over to
them.

I was working one theatre where there was a small pyrotechnic charge used. I
watched the stage crew prepping it and using a length of 24awg copper wire
as the initiator - conected directly to the dimmer circuit. Thought it would
blow the dimmer for sure.... darn, those things are robust now!

Oppie

On Thu, 19 Apr 2007 12:07:25 -0700, Jim Thompson
wrote:


output with the turn of a dial.

I have been "backstage" for at least 40 years. Back then I recall
big-ass chokes with a moveable core to change the inductance.

...Jim Thompson

And the big 'board' with many knobs to adjust lights... g Whether an
adjustable inductor, or a Variac, those things were big--lot's of
power involved.

Oppie wrote:

Anybody remember the name of the ancient dimmer that used a variable
inductor in series with the lighting circuit?

The chorus that I sing with is performing in a turn of the last century
theatre. I was marvelling at the ancient stage technology. They still have
the old style sandbag counterweights and belaying pins to anchor the lines
though the lines themselves have been changed from the original hemp lines
(guess they were all smoked by now...) to new black cotton lines that
conform to newer codes. The original lighting panel has long since been
replaced by a new digital board but I was talking with the theatre manager
and trying to remember some of the old names.

Rheostats, the original dimmer technology were replaced by the variable
inductor types to some extent. All of these were eventually replaced by
Variac types for many years until the newer electronic dimmers took hold.
I have fond memories of high school stage crew, running the Variac dimmer
board. On scene changes, the dimmers could be mechanically ganged into a
master group and master groups could be ganged to the grand master.
Sometimes it took two people to pull the grand master - and it had a 4 foot
handle. Oh, to have had a DMX back then.

Oppie
www.chordsmen.org


When I read the subject of this thread, I thought was Eeyore's life
story.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

"Oppie" wrote in message
...

The Variac was a trade name for an adjustable autotransformer. I haven't
seen a variac board in any theatre in the last 25 years. The cost of
electronic controls has come down so much that everybody converted over to
them.

I was working one theatre where there was a small pyrotechnic charge used.
I watched the stage crew prepping it and using a length of 24awg copper
wire as the initiator - conected directly to the dimmer circuit. Thought
it would blow the dimmer for sure.... darn, those things are robust now!

In some European theatres they used a single variable transformer with a
high voltage primary (like 11 kV) and a number of secondary sliders all run
via remote control flexible cables like bicycle brake lines. The transformer
was in a cage with the mechanical and electrical lines run into it.

output with the turn of a dial.

I have been "backstage" for at least 40 years. Back then I recall
big-ass chokes with a moveable core to change the inductance.

...Jim Thompson
I think that is working the same as variable control current. The
simplicity is tough to beat!

There are tiny sensors that use the same principles to detect
mechanical position. The one I remember worked at a higher (than line)
frequency. It was very precise.
John Ferrell W8CCW
"Life is easier if you learn to
plow around the stumps"

John Ferrell wrote:

On Thu, 19 Apr 2007 12:00:34 -0400, "Oppie"
wrote:

Anybody remember the name of the ancient dimmer that used a variable
inductor in series with the lighting circuit?

The chorus that I sing with is performing in a turn of the last century
theatre. I was marvelling at the ancient stage technology. They still have
the old style sandbag counterweights and belaying pins to anchor the lines
though the lines themselves have been changed from the original hemp lines
(guess they were all smoked by now...) to new black cotton lines that
conform to newer codes. The original lighting panel has long since been
replaced by a new digital board but I was talking with the theatre manager
and trying to remember some of the old names.

Rheostats, the original dimmer technology were replaced by the variable
inductor types to some extent. All of these were eventually replaced by
Variac types for many years until the newer electronic dimmers took hold.
I have fond memories of high school stage crew, running the Variac dimmer
board. On scene changes, the dimmers could be mechanically ganged into a
master group and master groups could be ganged to the grand master.
Sometimes it took two people to pull the grand master - and it had a 4 foot
handle. Oh, to have had a DMX back then.

Oppie
www.chordsmen.org


As I recall, the saturable reactor was a transformer with two
windings. One of the windings was in series with the input power to
the lights. The other winding was provided with a variable DC power.
When there was no DC present, the other winding was high impedance to
the lamp loads. When the DC was applied the core in the transformer
was saturated and the impedance went down as the lights came up!

What sort of 'dynamic range' do these things have? How close to zero
output can the lights be set? On the other end, how close to 100%?

Variac control can go from 0 to something over 100% (I have one with a
110% tap).

--
Paul Hovnanian
------------------------------------------------------------------
Power corrupts. And atomic power corrupts atomically.

"Paul Hovnanian P.E." wrote in message
...

What sort of 'dynamic range' do these things have? How close to zero
output can the lights be set? On the other end, how close to 100%?

The 'catch' is that the reactor needs to be sized to the load. You don't get
that with SCRs.

"Paul Hovnanian P.E." wrote in message
...

What sort of 'dynamic range' do these things have? How close to zero
output can the lights be set? On the other end, how close to 100%?

Variac control can go from 0 to something over 100% (I have one with a
110% tap).


Reactors and rheostats were both an impedance that was inserted in series
with the lighting load. They had some severe limitations in how they could
be used and the useful dimming range that could be achieved. When the Variac
(originally trademarked by General Radio, 1934-2002 ) came out, it was
almost immediately accepted as the preferred means of dimming. The Variac
was still preferred for dimming in the early days of SCR dimmers for a
couple of reasons. Early SCR dimmers simply were not robust enough for live
use. When a lamp blows, the filament vaporizes and for an instant, a low
impedance arc forms. That often draws enough current to cause a SCR to short
out. The other reason was the nasty risetimes that were both radiated from
all wiring and coupled back to the line... all of which wrecked havoc on
live sound systems. I spent way too much time trying to phase the lines and
lifting/moving grounds on the sound systems to minimize buzz from the
dimming systems.

btw- I remember seeing ganged Variacs that were motor driven to dim very
large loads like the theatre house lights. Was neat at the time to have
pushbutton dimming (two buttons: one for dim/down and the other for
brite/up)

Oppie