Discuss Oldest domestic dimmer switch in the Electrical Forum area at ElectriciansForums.net

Lucien Nunes

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What is the oldest dimmer switch you have seen in use recently?
When did you install your first dimmer? (Veteran sparks only)

I ask because a friend recently sent me a link to a 'news' story about an old toaster still in use, which I don't even really see as an old toaster (OK, yes, it's older than my daily use toaster but I have much older working toasters.) There are quite a few of these stories around, where people find something from the 1950s still giving service and think that's remarkable. But what about the humble, unobtrusive knob on the wall?

I have one old dimmer still in use at home, it's a 'Crescent 2' 300W model which probably dates from the late 1960s. I haven't been able to pin it down any tighter from the components, but if I trawl some magazines of the era I think there are ads for this specific dimmer. Mounted on MK rounded corner face plates, they use an old circuit based on a stud thyristor inside a bridge rectifier, triggered by a germanium transistor, instead of a triac triggered by a diac which has been standard since the 1970s. This has the disadvantage of two extra diode-drops so higher heat dissipation, but the advantage of absolute firing symmetry. I see flicker very easily and can spot a diac-triggered triac dimmer that has a 50Hz component in its output due to slightly different triggering voltages on the two half-waves.

We had five of these at one time, some were retired with the coming of the CFL, another replaced with an IR remote-controlled one, etc. One did fail with a leaky AC128. The last one is likely to get retired soon as I want to try LED in this fitting that is on for many hours a day and will need a compatible dimmer. At the moment the Crescent 2 is dimming a 150W GLS lamp, it has had up to 200W (often 2x 100W in a bayonet Y-adaptor) as it's a key light source in the lounge. The main reason the Crescent has survived so long is the high quality Allen-Bradley pots they used, which never seem to wear out.

Let's see your old dimmers. I have a soft spot for the edge-thumbwheel-controlled MKs of the 70s-80s with the separate switch. I don't think we have any in the collection though.

Oldest domestic dimmer switch 20220120_221533 - EletriciansForums.net
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Oldest domestic dimmer switch 20220120_233736 - EletriciansForums.net
 
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littlespark

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Now you’ve taken it off the wall, I bet it doesn’t work when you put it back…

Can’t say I’ve seen anything like that. Even when I started late 80’s, existing dimmers were exactly as we have them now.
 

marconi

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My uncle, an electronics buff, gave me several boxes of Radio Constructor magazines as a young teenager. In one was a project to build a thyristor dimmer using the leading edge phase trigger control technology you mentioned of a thyristor inside a bridge rectifier with a pot, capacitor and transistor time delay. I made it and it did indeed dim the only light in the living room, a pendant with a 100W lamp. It overheated/behaved erratically if I used a 150W lamp. It had to be consigned to history because it produced terrible electromagnetic interference to the radios in our home and our neighbours which I as a 12 year old in 1973 was not able to eradicate or suppress despite one or two attempts with chokes and shielding. The radios would have been AM. We did not have a hifi then.

Does not your Crescent 2 (300W) do the same to your radio sets or has FM and DAB come to your rescue?

You will like to read Spira(SCR)and Alessio(triac):

History of the Dimmer Switch - https://kbelectricpa.com/history-dimmer-switch/

Solving the Phase-Cut Dimming Challenge — LED professional - LED Lighting Technology, Application Magazine - https://www.led-professional.com/resources-1/articles/solving-the-phase-cut-dimming-challenge
 
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Lucien Nunes

Lucien Nunes

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I've not been aware of any RFI issues with the Crescent dimmers but I just ran a simple practical test using a Bush DAC10 held up close to the dimmer and wiring (T+E in stud wall.) On MW with no station tuned, there is a small amount of buzz audible in the middle of the dimming range although not at full. With even a weak station tuned, by the point the AVC starts to take effect, no interference is audible nor is the tuned RF level affected.

I tried the same test with a modern MK 500W leading-edge dimmer in another room, loaded with 100W, and the buzz was very much louder and also marginally present with a weak station tuned. Not an accurately controlled comparison but it suggests the Crescent dimmer is no worse for RFI, and possibly quite a lot better, than the MK.

In the Crescent, the incoming connections pass through a pair of ferrite-rod chokes of perhaps 100 μH, with 1kΩ + 0.1 μF inboard of them across the bridge input. Nothing remarkable there.

Oldest domestic dimmer switch 20220121_202149 - EletriciansForums.net
 
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Avo Mk8

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Apologies for sligtly off topic, but as a young teenager, my first 'dimmer' (actually "rheostat" I guess) came with another larger one on a black bakelite panel from Proops in Tottenham Court Road in the early 1960's, surplus wartime stock, as used in Lancaster bombers etc. Cost probably a shilling or two. I used it on my model railway to control the LV lighting.
Oldest domestic dimmer switch 22DC7287-26CF-45FB-A4F4-871519F0577D - EletriciansForums.net
The ultimate trip to London would comprise visiting the large number of shops in Lisle Street and Tottenham Court Road selling the most amazing array of wartime surplus electronics, for not much money, receivers, transmitters, parts thereof, telephony, RTTY, aircraft and vehicle based components of every sort. Boxes of stuff spilling out onto the pavements. Everywhere was an Aladdins Cave!

My first foray into 'solid state' dimming was to construct a circuit (which I imagine I found in "Practical Wireless") inside a 3 pin adapter, to control the speed of a mains powered drill, before the days they were designed in. Circuit used a neon bulb to trigger the thyristor, similar to below (but UK version!) 🤭
I don't think it created RF interference, at least none that I was aware of!
Oldest domestic dimmer switch 3C2E0E60-5314-4067-AE9F-7DFCBE1945A9 - EletriciansForums.net
Happy days!
 

Dave OCD

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Lucien, I can remember installing quite a few of the MK thumbwheel dimmers with separate switch , expensive at the time !
Strangely to me there was a 'fixed load' and 'variable load' terminal and I misinterpreted this when fitting my first one, connecting the light to fixed load....🙂 Could never really see the point in why you'd want to have more than one light in the same room switched together with one dimming and the other/s staying at full wallop ?
 
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Lucien Nunes

Lucien Nunes

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Two possibilities come to mind. One is that before dimmers, there were fixtures with multiple lamps split between two feeds, e.g. a 6-lamp electrolier with two lamps on one feed and four on the other, which would be controlled from two switches for 1/3, 2/3 and full options. Replacing the double switch with the MK dimmer would allow you to put 1/3 on fixed and 2/3 on the dimmer, so you could vary from 1/3 to full without losing the colour temperature and efficiency at the 1/3 setting because there's still the two lamps at full brightness. The other which is a bit far-fetched is whether they were compatible with dimmable fluorescents, which need a fixed feed for the heater transformer as well as the dimmable feed. But they also need a high / adjustable minimum level setting to stop them flickering and going out, and AFAIK the MK dimmer didn't have this, plus, fluo dimmers normally need hard firing.

But I expect the reason is that the switch was made from standard parts and the common terminal was already there so they let it show through the housing in case it came in useful some time. Dimmers with 1-way switching like the Crescent, could use generic SPST or DPST switched pots as widely used in electronic goods for on/off/volume. But for 2-way switching there were no generic 2-way (SPDT) switched pots, so using a separate conventional 2-way switch was the solution until the pot manufacturers caught up.

IIRC there was another brand, possibly WG, that had the fixed / common terminal accessible, as well as the separate switch & control knob layout.
 
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brianmoooore

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The ultimate trip to London would comprise visiting the large number of shops in Lisle Street and Tottenham Court Road selling the most amazing array of wartime surplus electronics, for not much money, receivers, transmitters, parts thereof, telephony, RTTY, aircraft and vehicle based components of every sort. Boxes of stuff spilling out onto the pavements. Everywhere was an Aladdins Cave!

My first foray into 'solid state' dimming was to construct a circuit (which I imagine I found in "Practical Wireless") inside a 3 pin adapter, to control the speed of a mains powered drill, before the days they were designed in. Circuit used a neon bulb to trigger the thyristor, similar to below (but UK version!) 🤭
I don't think it created RF interference, at least none that I was aware of!
View attachment 94213
Happy days!
Still lots of bits from Tottenham Court Road in one of my attics, including a couple of modified WS19s.
I also made up a Practical Wireless or might have been Radio Constructor drill speed controller into a die cast aluminium box, and it's still going strong today.
Hadn't been used since the advent of drills with built in speed control, but last year I needed to get a circular saw into a tight space, so fitted a saw blade into my 9" grinder. Far too fast of course, so I dug out and dusted off the old box, plugged it in and it controlled the grinder speed perfectly.
 

brianmoooore

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Back when these were current, I was given a large box of MK 'returns'. This neighbour had a best mate who was a foreman on the local council's refuse collection operation, so it was probably trade 'waste' from one of the local wholesalers, that MK had told them to dispose of.
The box contained several of these dimmers, several bathroom shaver sockets, and loads of less valuable bits like sockets and switches.
Extensive testing showed that a lot of it had no faults at all - in the case of the dimmers, I expect the problem was that they flickered because of insufficient load.
Anyway, Lucien, yesterday, I turned out the box, from it's place at the back of a high shelf in the workshop, and there are two there, complete with (somewhat tatty) boxes and instruction leaflets, which are yours, if you want them. I don't know if they are in working order or not, but I also have a third one, definitely in full working order, that I fitted, a very long time ago, in the bedroom that I grew up in. This is now part of the farmhouse I have spent the last couple of years extensively upgrading and re working. Most of the original wiring has been ripped out, but I've kept some of the lights in service as work lights, with the cables strung up with bits of string and hanging like washing lines across the rooms.
LED lamps were been fitted everywhere when I started work, and the dimmer section was taken out of circuit, just using the switch section. You can have this one as well, if you want it. It would only take me a couple of minutes to swap it for an ordinary switch.
 

Bob Geldoff1234

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My father rewired Blackpool Town Hall in the 1980's.The building was one of the first to get electrics in 1900 and was wired in lead with waxed paper as the insulator.The joints were put into a metal box,the lead clamped and the wires stripped bare and jointed with porcelain screw it joints.The whole joint box was then filled with hot bitumen to seal the box for life.
Anyway,the reason for this post is that they had a chandelier in the main entrance which had a very high ceiling and beneath was a statue of Queen Victoria.As it was near impossible to get to the bulbs to replace them,they needed to lower the voltage to the bulbs so that they lasted longer.Dimmers didn't exist I dont think in 1900 so they wired 2 bulbs in series with the chandelier.These bulbs were placed in the gents toilets nearby so, when the chandelier was on,so were the bulbs in the toilet.The chandelier bulbs run at a much reduced voltage and fulfilled the purpose of a dimmer.
 

brianmoooore

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You can often pick up stuff like this on Ebay

You'd think so, but I couldn't find a single image of the dimmer switch in question anywhere on the web. The link you posted is the nearest, but that's the grid version. Doesn't help that MK have 'recycled' the part number several times.
 
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Lucien Nunes

Lucien Nunes

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@brianmoooore that's a very kind offer that I will take you up on, and thereby tick off one of my 87 million must-haves from the museum list. Of course it's part of the bigger picture of making up a complete set of MK accessories in each of their hallmark styles, but as I mentioned it's a personal favourite because when I was young and first saw one, the edge-control struck me as being much neater and more in keeping with the general style of light switches than a sticky-out rotary knob.

I'll PM you about postage etc and how to reimburse for same.

@Bob Geldoff1234 I wish we could have saved some of that gear!
 

brianmoooore

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@Lucien Nunes : Been looking through the rest of the box, and found this, which must be almost as old as yours.
Again, condition unknown, but yours if you want it.
Send me an address and I'll get it all posted to you, although it might take a while, since I'm still isolating from society, on account of my wife, so will have to get my son to post it, and his partner has just tested positive for you know what.
Do you want both boxed dimmers, the known working one and the one in this post?
Don't worry about postage costs. I'm sure the business can stand paying for that.
Just get on and get the museum up and running, so that I can visit it, meet you, and hopefully see my dimmers on display.
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