Vintage Lighting 1920s Lighting Controls?

[derekleffew]

...20% number has to be an error as the light would be on quite a bit!...

You are correct (see how advantageous it is to have others proofread one's wiki entries?), that should have read "the load had to be within 20% of the rating", (thus 80%); quote and article edited.

You've reminded me of something: On some models, at the low end the last contact would switch off the circuit, thus the "jump" ("non-bink dimming" option of the Cyberlight) would be from zero to 1%, not unlike some lesser-quality LED fixtures of today.

From Lighting the Stage, Art and Practice, Bellman, pp174-175:

How the Resistance Dimmer Works
The resistance dimmer operates by gradually inserting additional resistance into the lamp circuit until current flow is reduced sufficiently. Since the remaining current is still flowing through both the dimmer and the lamp, both still heat up. The dimmer heats the most because it has the largest share of the resistance. Heat will be generated according to the heat formula.

At intermediate points between full on and blackout, the resistance wire in the dimmer will be asked to carry larger amperages, although over less resistance. Since the heat will vary by the square of the amperage, these large amperages will produce still larger quantities of heat. Thus resistance dimmers get hotter at intermediate points than they do at blackout. Moreover, many good resistance dimmers have a flipper switch at the low reading point that cuts off the remaining current completely.

Load Sensitivity
All resistance dimmers are load sensitive because of the inescapable mathematics of resistance circuitry. The "four times the resistance of the lamp" ration can be satisfied for any given lamp load with only one dimmer size. For example, a 1000-watt lamp draws 9.33 amperes at 120 volts: W/V=A or 1000/120=9.33 ...

Poor Willard's slide rule must have been low on battery when he wrote that! Since all his further calculations of resistance are based on the erroneous values, I won't continue quoting, but his point is that it takes four times the resistance to dim a lamp to zero.

 

[JD]

but his point is that it takes four times the resistance to dim a lamp to zero.

Yea, I don't know why 10 is stuck in my mind, but it has been since 1969 when I last touched one. Sometimes time takes its toll on memories. I have a great book from the 60's on lighting, so you can imagine what "state of the art" was for this book! (Let alone the "history" section.)

I do not remember throwing that book out and may have to dig quite a bit to find it, but it will probably be fun to give it another read!

EDIT:
I can't believe it, I found the book! (Sometimes my memory actually works!!) It is called "Scene Design and Stage Lighting" by W. Oren Parker and Harvey K. Smith (copyright 1963, 1968)

Has some great pictures that I will have to scan sometime. It also has a history of pre-SCR electronic dimmers! How many remember the following types of dimmers? :

1) The Saturable Core Reactor Dimmer
2) The Thyratron Tube Dimmer
3) The Magnetic Amplifier Dimmer

The section ends talking about the most promising new technology, "A silicon rectifier under control."

 

[MPowers]

As others have said, middle/late 50's earliest, late 60's latest. The Red wheel is a master. It took a bit of effort, small, to move one handle, but to dim or increase several or many required a lot of force, thus the geared master handle.

It is indeed an auto transformer type of board, looks like a Ward Leonard board.

 

[David Ashton]

Sorry john but

There is actually an old lighting book I have somewhere that deals with the math. The low end "squelch" was aided by the fact that filaments drop in resistance as they near the cold state. This may explain why some under-loading was ok. (cold lamp would be "relative" as tungsten does not start its resistance climb until about 600 degrees F)

the resistance climb, as you call it is linear at any range you're going to find in our world.The lamp curve is a mixture of volts, amps and the resistance change with increasing temperature, but the underlying temperature/resistance coefficient is linear.

 

[church]

Yea, I don't know why 10 is stuck in my mind, but it has been since 1969 when I last touched one. Sometimes time takes its toll on memories. I have a great book from the 60's on lighting, so you can imagine what "state of the art" was for this book! (Let alone the "history" section.)

I do not remember throwing that book out and may have to dig quite a bit to find it, but it will probably be fun to give it another read!

EDIT:
I can't believe it, I found the book! (Sometimes my memory actually works!!) It is called "Scene Design and Stage Lighting" by W. Oren Parker and Harvey K. Smith (copyright 1963, 1968)

Has some great pictures that I will have to scan sometime. It also has a history of pre-SCR electronic dimmers! How many remember the following types of dimmers? :

1) The Saturable Core Reactor Dimmer
2) The Thyratron Tube Dimmer
3) The Magnetic Amplifier Dimmer

The section ends talking about the most promising new technology, "A silicon rectifier under control."

I remember the Saturable Core Reactor Dimmer. I used one in the 70s when I was a teenager - am I really that old now? I am now going to find a dark corner and curl up in the fetal position and moan quietly for an hour or so.

 

[JD]

I remember the Saturable Core Reactor Dimmer. I used one in the 70s when I was a teenager - am I really that old now? I am now going to find a dark corner and curl up in the fetal position and moan quietly for an hour or so.

The Saturable Core and "Magnetic Amplifier" work on similar concepts by over saturating the core with a DC field, chopping the waveform which came out looking like a square wave. I never had the privilege of seeing one in person, and have some conceptual problems imagining how the DC field effects the AC waveform in any symmetrical way that makes sense! Must have worked though...

Thyratrons, I have actually seen and they are cool and colorful to watch as the gas tubes fire into conduction.

In this book, the number used as a multiple for squelch was 5. Apparently, there were plates that used two loops on the same platter, one for 1500 and the other for 3000. I will scan and post a pic they have of one later.

The comment I loved was near the end of the article where SCR dimmers were considered unsuitable and limited as most Broadway theaters still run DC !

 

[derekleffew]

... I can't believe it, I found the book! (Sometimes my memory actually works!!) It is called Scene Design and Stage Lighting by W. Oren Parker and Harvey K. Smith (copyright 1963, 1968) ...

Colloquially called "Parker and Smith", that (the ©1979 edition) was my textbook for Stagecraft 101 freshman year in college. Today it is known as Parker and Wolf--I suspect they've deleted the chapters on other-than-phase-control dimmers. I wonder if they still cover the stage brace and lash-line hardware?

...The comment I loved was near the end of the article where SCR dimmers were considered unsuitable and limited as most Broadway theaters still run DC !

We had a thread just a few years ago on the last POCO in the US to supply DC power. (Can't find it now.) Grease (1972-1980) is credited with the last Broadway show to use piano boards, though we don't know if that was due to lack of available AC or for financial reasons.

I've been told My Fair Lady (1956) was the first Broadway show to use Dimmer, Autotransformers, which, along with all subsequent dimmers, only work on AC.

 

[JD]

Sorry john but
the resistance climb, as you call it is linear at any range you're going to find in our world.The lamp curve is a mixture of volts, amps and the resistance change with increasing temperature, but the underlying temperature/resistance coefficient is linear.

Ahh, but what you neglected to factor in is that one resistance is increasing as the other is decreasing, which produces anything but a liner curve! Take this example where one value goes from 1 to 10 while the other goes from 10 to 1:

 

[theatreguy]

Wow, this reminds me of the distribution panel in a theatre I volunteer at that was built in 1927. The majority of the power was rerouted to other places with only a few circuits being used in it to roue power to the dressing rooms. Unfortunately, we had a water pipe burst a few days ago which flooded it and now it has been disconnected and the power that went ot it, re routed.

Here is one picture of it. I plan to take more extensive pictures in the next couple days.

 

[STEVETERRY]

The Saturable Core and "Magnetic Amplifier" work on similar concepts by over saturating the core with a DC field, chopping the waveform which came out looking like a square wave. I never had the privilege of seeing one in person, and have some conceptual problems imagining how the DC field effects the AC waveform in any symmetrical way that makes sense! Must have worked though... !

They did indeed....and still do. After the recent 2009 renovation of the New York State Theatre at Lincoln Center, a 3-phase 100 amp Kliegl saturable-core reactor survived to drive the lobby lights.

This was because the rather odd wiring topology feeding those loads and associated code issues (a three phase 100 amp dimmer feeding multiple 3 phase breaker panels with 15A branch circuits) were discovered too late in the renovation to add them to the more than 1,800 Sensor dimmers that replaced the original 1963 Kliegl SCR and reactor system.

ST