mains lead

[mikej56]

It's not unusual to aquire an old radio or other electronic equipment which has the mains lead missing, and a replacement is impossible to obtain.
This was the case recently when I was kindly given a Vega Selena set, by Philsync. The old war-time phrase 'make do and mend' came to mind, so I decided to have a go at making up a lead for this set. This is the result.

[Sam]

It looks like you have made an excellent job of it - certainly better than the attempts you see on eBay now and then!

Sam

[Nickthedentist]

Good stuff, Mike! I've often thought of doing the same, perhaps using some of the light-cured composite materials that we dentists can get our hands on. Now I've seen your success story, I'll be more optimistic about having a go myself

[mikej56]

Thanks Guys,
Nick, I don't know if you guys still have denture making facilities on your premises, but I remember that material that the denture gums were made of, acrylic I think, my dad used to use it for all sorts of things. It would be ideal for something like this.

michael

[Nickthedentist]

Some dentists do, but not us - we send all our work to an outside lab.

The denture material you're talking about is indeed acrylic, also known as poly-methyl methacrylate (I think!). The liquid component (the monomer) has got a very pungent smell and is reputed to lead to Parkinson's-like symptoms if you breathe in the vapour too much over a period of many years. Certainly one of my friends who is only in his late 50s and had been a denture technician all his career, is now in a very bad way because of this . Having said that, as with most things, making the odd plug or two shouldn't be a problem

The composite materials I was referring to are very costly indeed in real terms, but are great because you can mould them to shape, then "zap" them with a bright blue light, instantly turning them from a soft putty to an extremely strong, hard material. Their "official" use is for white fillings, usually on front teeth.

Nick.

[joe]

poly-methyl methacrylate (I think!)

I believe that this is the chemical name for "Perspex", which is of course an acrylic.

I asked my dentist about moulding materials, mainly with replacement knobs in mind, and via his dental lab found a company that supplies all kinds of moulding materials, but the cost was frightening especially as the stuff had a very limited shelf life.

Joe

[GMB]

I can confirm that poly methyl methacrylate is indeed what is trademarked as Perspex.

It is quite easy to make methyl methacrylate, I used to do this when I was a boy. Just distill some Perspex. It depolymerises on heating - that's why it smells when you drill it too fast or with the wrong kind of drill. Pure methyl methacrylate is a colourless liquid (like water). I have seen commercial bottles of it for use in the plastics industry and there it is more viscous which means it has been partly polymerised already, to make it easier to use.

I seem to remember that the polymerisation is a free-radical reaction so anything will kick it off and once going it all sets very quickly. UV light is the nice clean way to do it but a radical starter like used for GRP will work too. That's why it's so hard to store.

[Nickthedentist]

Originally Posted by joe

I asked my dentist about moulding materials, mainly with replacement knobs in mind, and via his dental lab found a company that supplies all kinds of moulding materials, but the cost was frightening especially as the stuff had a very limited shelf life.

Sadly, everything marketed for the dental profession is staggeringly costly. For example: The "bonding agent" which we use as a primer to attach white fillings to teeth costs over £50 for a 4mL bottle - which becomes useless in a day if the lid is left open a fraction

[ppppenguin]

What's wrong with the universal "13A plug to crocodile clips" mains lead

Nick, is dental stuff so expensive because it's genuinely costly or is it a monopoly/collusion? I suppose it explains why dental treatment is not exactly cheap. Or are the materials costs fairly small compared to staff and premises costs so the materials suppliers can get away with it.

[Nickthedentist]

Originally Posted by ppppenguin

Nick, is dental stuff so expensive because it's genuinely costly or is it a monopoly/collusion? I suppose it explains why dental treatment is not exactly cheap. Or are the materials costs fairly small compared to staff and premises costs so the materials suppliers can get away with it.

Jeffrey, reasons cited are:
1. It's "high-tec" stuff, so of course it's costly!
2. There is a limited market, so there is little economy of scale.
3. It has to be tested and approved by goodness-knows-how-many agencies, which bumps up the prices.

There are many different manufacturers, but a very limited number of supply companies (some owned by the same parent company), so your monopoly theory may be valid. Having said that, I'm told that the biggest expense in running a dental practice is staff wages, followed by rental of the premises. Materials costs are relatively small.

What do people think about connectors that use flat pins? Can anyone suggest a suitable receptacle to incorporate into a custom-made connector?

And approximately how long did it take you to put this connector together, Mike?

Nick.

[mikej56]

Hi Nick,

I cant say exactly how long my effort took, because i had to wait quite a time for the epoxy to set.
Could you elaborate on the flat pins?

regards

michael

[Nickthedentist]

Originally Posted by mikej56

Could you elaborate on the flat pins?

What I meant was that most chassis connectors have round pins, for which it is quite easy to find a mating connector, just like in the case you described.

But some have flat pins (just like the standard IEC connector found on computer hardware etc.), and I can't think of anything that would be able to mate with those very well.

Nick.

[ppppenguin]

Perhaps some fairly drastic surgery on IEC connectors?

US mains connectors have flat pins. Maybe the sockets could be butchered. Likewise Israeli ones.

[mikej56]

I can't think of any male sockets with flat/square pins that aren't the standard IEC type for which there wouldnt be a ready made plug, do you have an example?

[Nickthedentist]

Thanks for your ideas, Jeffrey.

And Mike, no I haven't got one to hand, but I've definitely seen them on obscure imported 1960s gear.

Your technique would also be useful to electric clock enthusiasts like me. All too often, the clocks turn up without the mating connector. 9 times out of 10, it's a standard Smiths/SEC/Sectric item, but sometimes it's unique and impossible to track down.

Nick.

[mikej56]

Nick, if you can get a drawing of the clock thing, I think I saw one years ago, I'd have a go at designing a connector.
To take Jeffrey's Idea you could strip the pins out of an IEC plug, since they are cheap.
The hard bit is opening the crimps so that they can be re-used, It must have taken me half an hour to prepare the round ones in the mains lead.

[Nickthedentist]

Originally Posted by mikej56

The hard bit is opening the crimps so that they can be re-used, It must have taken me half an hour to prepare the round ones in the mains lead.

CPC sell the type you used, ready to crimp, in bags of 100 I think. But I can't find them in the new "easy-to-use" catalogue

[mikej56]

LoL ! I'll have to keep my eyes opened in future, I just didnt think of looking for them in cpc. So now I'll go and hunt for rectangular ones

[jim_beacon]

There are a few American sockets with flat pins, Tek used them as power inputs on a lot of their gear, and they are difficult to find in the UK. I think I've seen falat pins on some European stuff as well, but not common.

Jim.

[Nickthedentist]

Originally Posted by jim_beacon

Tek used them as power inputs on a lot of their gearJim.

Ah yes, that was one of the places I'd seen them recently.