Why do they use mains connectors? - UK Vintage Radio Repair and Restoration Discussion Forum

Tractorfan · 2nd Nov 2010, 6:35 pm

Hi,
Much has been discussed about DAC90A mains connectors and those of other radio & TV sets, and this set me wondering why they were used at all? Were they meant to be some kind of "interlock" to ensure disconnection before removing the back? Considering that cost of production was usually a major factor in building these small sets, surely it would have been cheaper to take the lead straight in (and lessen the possibility of reversed polarity into the bargain). Some sets have detachable leads and others don't, which adds to the mystery

.
Cheers, Pete

PS Sorry if this has been done to death already

.

Sideband · 2nd Nov 2010, 8:17 pm

Don't know.....it's an interesting question though. Some manufacturers (Philips was one) designed mains connectors that were part of the back cover so when you removed the back, the mains was disconnected as well. This was purely from the customer viewpoint who wanted to change the odd valve. Service engineers would have had a connector made up so that they could work on the set.

SB

chipp1968 · 2nd Nov 2010, 11:38 pm

Is it more common on AC/DC sets?

oldticktock · 3rd Nov 2010, 7:46 am

Also why did the two pin plug vary as in those used on Bush, PYE, Decca and others ,then the odd EKCO two pin (on slim one fat)

3rd Nov 2010, 8:58 am

It may have worked out cheaper because it would be easier to power up on the line and there would be no lead flapping around in production.

fidobsa · 3rd Nov 2010, 9:07 am

On rented sets there may have been an advantage. If the cable got tugged it would just pull plug from socket rather than pulling conductors out of their terminals, resulting in a repair visit.

mark pirate · 3rd Nov 2010, 9:37 am

Quote:

the odd EKCO two pin (on slim one fat

This arrangement was a good idea, less chance of wrong polarity causing the chassis on ac/dc sets becoming live!
Bush should have adopted thi idea.
I would have thought that adding a removable mains lead would add to the production costs,so why it they were fitted is a bit of a mystery?
I have just got a dac 90 that someone has changed the lead to clear bellwire

at the other end was fitted a 'clix' two pin plug!
I prefer a fixed mains lead for this reason.

Mark

SeanStevens · 3rd Nov 2010, 10:16 am

More modern equipment (think of Cassette Players) usually had removable leads - this was, I guess, because they could be battery powered (portable) and the lead could be left at home.

But the DAC90 range was never designed to be portable surely?

Could it be that the lead could be used to power something else? There were very few mains sockets in older houses, could it be that the BUSH people thought you would take the lead out of the radio to power up a record deck or something?

SEAN

Mike Phelan · 3rd Nov 2010, 10:23 am

No, as most of these sockets were maker-specific, and other equipment tended to have permanently attached leads.

It is an interesting question!

Lucien Nunes · 3rd Nov 2010, 9:56 pm

Reversible connectors were useful if you had DC mains. These days we look at a transformerless design as just an economy measure but when the DAC90 was introduced there was still a bit of DC mains about and it was a necessity. With a DC supply the chassis has to be negative, regardless of which pole is live (on ordinary 3-wire DC mains half the houses had a positive live and half a negative, relative to the earthed neutral). So you set the voltage tap, plug the set in and if the heaters light up but no sound comes out flip the domino connector over to reverse the polarity.

With a mixture of 2- and 3-pin plugs widely in use and much of the wiring in DC areas remaining from pre-electronic days, there would be no certainty even of knowing which contact in a given socket-outlet was live, let alone whether it was positive or negative. We have become accustomed to ensuring the chassis wire is neutral for safety, as we have this option on AC. But on DC if your live was negative then the chassis definitely had to be live.

Lucien

Tractorfan · 3rd Nov 2010, 10:33 pm

Hi,
Thanks for the interesting info, Lucien, but it doesn't explain the non-reversible connectors found on some Ekco equipments (amongst others). Maybe it was my suggestion that it ensured the supply was removed when the back was taken off.
Cheers, Pete

Lucien Nunes · 3rd Nov 2010, 11:45 pm

Yes I'm sure that was a factor. E.g. the type with the two prongs in a shallow V, had a flange around the outside of the cable socket to ensure it would pull off with the TV back even though it wasn't attached to it. Some manufacturers have gone to even greater lengths to isolate the innards when exposed. E.g. to get a Revox A77 out of its box you first have to remove the mains cable. But once out, even if you plug the cable back into the chassis it will be dead until you bridge the interlock terminals that are normally shorted by pins attached to the back.

On professional / broadcast kit connectors have been the norm, rarely for safety reasons as you can often open the box without disconnecting. But then there would not be the same risk as with a live-chassis TV in a domestic environment. The lack of standardisation until recently nullified some of the advantages of interchangeable / replaceable cables. Going back to the 60's & 70's, the different wiring conventions of EP4 (Marconi / BBC) and the two possible genders of XLR-LNE were amongst the various traps for the unwary.

I wonder how the previous experience of designers influenced their decision whether to include a connector or not? I don't think I have ever made a product with a captive power cable, because of experience of mission-critical devices being put out of action due to damage that could easily have been remedied by the user swapping in a new cable. So if I were going to design a tabletop valve radio, I'd probably put a connector on out of habit, feeling it to be good practice, and argue my case with the bean-counters.

Lucien

Radio_Dave · 4th Nov 2010, 12:41 am

Interesting question but it's worth remembering that plug in mains leads are just as popular today (if not more so). The answer is, probably, going to be something as simple as ease of packaging etc

SeanStevens · 4th Nov 2010, 10:32 am

Or possibly they had a lot of left-overs. Manufacturers have a habit of 'using up' old stock by putting the same old gear on their newer models to reduce waste.

DAC90 uses this cable I think, so it makes sense if you have ordered 1000's too many of these mains lead ends, to use them up on the 90a.

SEAN

richrussell · 4th Nov 2010, 11:02 am

I reckon a combination of factors, but not probably assembly and packaging being quite a strong influence. It's certainly a lot easier if you don't have trailing wires if you have any kind of assembly line setup, as they tend to snag on things. Similarly with packaging - it's easier to slot a rectangular box shaped thing into the packaging if you don't have to worry about a bundled up cable dangling out of it.

These days places produce products that may be sold in any number of countries with different mains leads, so it's fairly sensible to just chuck in a UK lead for ones destined for the UK at the time of packing.

Heatercathodeshort · 4th Nov 2010, 11:20 am

As Lucien says, a look at all the original connectors used by manufacturers of AC/DC equipment in particular fitted flanges so the mains had to be disconnected before the back could be removed. EKCO and FERGUSON used the odd sized pins to ensure that the 'polarity' was correct to the chassis. eg the black wire. I would say that at least 80% of homes ran equipment from 2 pin socket outlets so this was not so important.
The 5amp connector that most of us use today is the female half of a flex connector and was not intended to be used as a mains input connector for receivers. Regards, John.

brianc · 4th Nov 2010, 12:58 pm

The early Pyes, LV20 etc. had another way of disconnecting the mains when the back was removed. They had a fixed mains cable but the back was fitted with two "floating" brass pins which, when the back was in place, completed the mains path (in both "legs"). When the back was removed, the pins came with it and the mains circuit was broken. In order to power the set without the back, pins had to be inserted in the holes in the rear of the chassis - I use 4mm banana plugs!

Brian R Pateman · 4th Nov 2010, 1:21 pm

Quote:

Originally Posted by brianc

The early Pyes, LV20 etc. had another way of disconnecting the mains when the back was removed.

At least one of the post war mains / battery portables uses exactly the same method. PB129 I think.

Welsh Anorak · 4th Nov 2010, 1:55 pm

Hi
As someone who got the mains lead of a colour TV I was delivering( a fairly new 26" Pye 741 - some things you don't forget) tangled around the car's bumper without my knowledge followed by an almighty CRASH I can only say I'm all in favour!
Also nowadays the appropriate lead for the country can be put in the box by the importer.
Glyn

dseymo1 · 4th Nov 2010, 7:20 pm

Another factor might have been the ease with which a longer lead could be fitted. The only mains socket in the room might well have been on the other side from the preferred location of the radio. Many users (and some dealers) would have simply twisted the ends of the existing lead onto those of an extension lead, and wrapped with insulating tape, but a re-wireable connector at least offered the opportunity to fit a longer flex.
Much easier for bench servicing a set too, when the customer's lead could have been fitted with any of a variety of mains plugs.

2nd Nov 2010, 6:35 pm	#1
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,184	Why do they use mains connectors? Hi, Much has been discussed about DAC90A mains connectors and those of other radio & TV sets, and this set me wondering why they were used at all? Were they meant to be some kind of "interlock" to ensure disconnection before removing the back? Considering that cost of production was usually a major factor in building these small sets, surely it would have been cheaper to take the lead straight in (and lessen the possibility of reversed polarity into the bargain). Some sets have detachable leads and others don't, which adds to the mystery . Cheers, Pete PS Sorry if this has been done to death already . __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

2nd Nov 2010, 8:17 pm	#2
Sideband Dekatron Join Date: Oct 2003 Location: Croydon, Surrey, UK. Posts: 7,580	Re: Why do they use mains connectors? Don't know.....it's an interesting question though. Some manufacturers (Philips was one) designed mains connectors that were part of the back cover so when you removed the back, the mains was disconnected as well. This was purely from the customer viewpoint who wanted to change the odd valve. Service engineers would have had a connector made up so that they could work on the set. SB __________________ There are lots of brilliant keyboard players and then there is Rick Wakeman.....

2nd Nov 2010, 11:38 pm	#3
chipp1968 Rest in Peace Join Date: Jul 2006 Location: Somerset, UK. Posts: 2,356	Re: Why do they use mains connectors? Is it more common on AC/DC sets?

3rd Nov 2010, 7:46 am	#4
oldticktock Retired Dormant Member Join Date: Nov 2009 Location: Weardale, UK. Posts: 1,981	Re: Why do they use mains connectors? Also why did the two pin plug vary as in those used on Bush, PYE, Decca and others ,then the odd EKCO two pin (on slim one fat)

3rd Nov 2010, 8:58 am	#5
Guest Guest Posts: n/a	Re: Why do they use mains connectors? It may have worked out cheaper because it would be easier to power up on the line and there would be no lead flapping around in production.

3rd Nov 2010, 9:07 am	#6
fidobsa Retired Dormant Member Join Date: Mar 2009 Location: Zala, Hungary Posts: 418	Re: Why do they use mains connectors? On rented sets there may have been an advantage. If the cable got tugged it would just pull plug from socket rather than pulling conductors out of their terminals, resulting in a repair visit.

3rd Nov 2010, 10:16 am	#8
SeanStevens Octode Join Date: Sep 2009 Location: Bath, Somerset, UK. Posts: 1,033	Re: Why do they use mains connectors? More modern equipment (think of Cassette Players) usually had removable leads - this was, I guess, because they could be battery powered (portable) and the lead could be left at home. But the DAC90 range was never designed to be portable surely? Could it be that the lead could be used to power something else? There were very few mains sockets in older houses, could it be that the BUSH people thought you would take the lead out of the radio to power up a record deck or something? SEAN __________________ There are only 10 types of people, those who understand the binary system, and those who don't.

3rd Nov 2010, 10:23 am	#9
Mike Phelan Dekatron Join Date: Nov 2003 Location: Near Leeds, West Yorkshire, UK Posts: 4,609	Re: Why do they use mains connectors? No, as most of these sockets were maker-specific, and other equipment tended to have permanently attached leads. It is an interesting question! __________________ Mike.

3rd Nov 2010, 9:56 pm	#10
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	Re: Why do they use mains connectors? Reversible connectors were useful if you had DC mains. These days we look at a transformerless design as just an economy measure but when the DAC90 was introduced there was still a bit of DC mains about and it was a necessity. With a DC supply the chassis has to be negative, regardless of which pole is live (on ordinary 3-wire DC mains half the houses had a positive live and half a negative, relative to the earthed neutral). So you set the voltage tap, plug the set in and if the heaters light up but no sound comes out flip the domino connector over to reverse the polarity. With a mixture of 2- and 3-pin plugs widely in use and much of the wiring in DC areas remaining from pre-electronic days, there would be no certainty even of knowing which contact in a given socket-outlet was live, let alone whether it was positive or negative. We have become accustomed to ensuring the chassis wire is neutral for safety, as we have this option on AC. But on DC if your live was negative then the chassis definitely had to be live. Lucien

3rd Nov 2010, 10:33 pm	#11
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,184	Re: Why do they use mains connectors? Hi, Thanks for the interesting info, Lucien, but it doesn't explain the non-reversible connectors found on some Ekco equipments (amongst others). Maybe it was my suggestion that it ensured the supply was removed when the back was taken off. Cheers, Pete __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

3rd Nov 2010, 11:45 pm	#12
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	Re: Why do they use mains connectors? Yes I'm sure that was a factor. E.g. the type with the two prongs in a shallow V, had a flange around the outside of the cable socket to ensure it would pull off with the TV back even though it wasn't attached to it. Some manufacturers have gone to even greater lengths to isolate the innards when exposed. E.g. to get a Revox A77 out of its box you first have to remove the mains cable. But once out, even if you plug the cable back into the chassis it will be dead until you bridge the interlock terminals that are normally shorted by pins attached to the back. On professional / broadcast kit connectors have been the norm, rarely for safety reasons as you can often open the box without disconnecting. But then there would not be the same risk as with a live-chassis TV in a domestic environment. The lack of standardisation until recently nullified some of the advantages of interchangeable / replaceable cables. Going back to the 60's & 70's, the different wiring conventions of EP4 (Marconi / BBC) and the two possible genders of XLR-LNE were amongst the various traps for the unwary. I wonder how the previous experience of designers influenced their decision whether to include a connector or not? I don't think I have ever made a product with a captive power cable, because of experience of mission-critical devices being put out of action due to damage that could easily have been remedied by the user swapping in a new cable. So if I were going to design a tabletop valve radio, I'd probably put a connector on out of habit, feeling it to be good practice, and argue my case with the bean-counters. Lucien

4th Nov 2010, 12:41 am	#13
Radio_Dave Nonode Join Date: Jun 2004 Location: Norwich, Norfolk, UK. Posts: 2,543	Re: Why do they use mains connectors? Interesting question but it's worth remembering that plug in mains leads are just as popular today (if not more so). The answer is, probably, going to be something as simple as ease of packaging etc

4th Nov 2010, 10:32 am	#14
SeanStevens Octode Join Date: Sep 2009 Location: Bath, Somerset, UK. Posts: 1,033	Re: Why do they use mains connectors? Or possibly they had a lot of left-overs. Manufacturers have a habit of 'using up' old stock by putting the same old gear on their newer models to reduce waste. DAC90 uses this cable I think, so it makes sense if you have ordered 1000's too many of these mains lead ends, to use them up on the 90a. SEAN __________________ There are only 10 types of people, those who understand the binary system, and those who don't.

4th Nov 2010, 11:02 am	#15
richrussell Heptode Join Date: Jul 2008 Location: Selby, North Yorkshire, UK. Posts: 979	Re: Why do they use mains connectors? I reckon a combination of factors, but not probably assembly and packaging being quite a strong influence. It's certainly a lot easier if you don't have trailing wires if you have any kind of assembly line setup, as they tend to snag on things. Similarly with packaging - it's easier to slot a rectangular box shaped thing into the packaging if you don't have to worry about a bundled up cable dangling out of it. These days places produce products that may be sold in any number of countries with different mains leads, so it's fairly sensible to just chuck in a UK lead for ones destined for the UK at the time of packing.

4th Nov 2010, 11:20 am	#16
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Why do they use mains connectors? As Lucien says, a look at all the original connectors used by manufacturers of AC/DC equipment in particular fitted flanges so the mains had to be disconnected before the back could be removed. EKCO and FERGUSON used the odd sized pins to ensure that the 'polarity' was correct to the chassis. eg the black wire. I would say that at least 80% of homes ran equipment from 2 pin socket outlets so this was not so important. The 5amp connector that most of us use today is the female half of a flex connector and was not intended to be used as a mains input connector for receivers. Regards, John.

4th Nov 2010, 12:58 pm	#17
brianc Rest in Peace Join Date: Jun 2004 Location: Burghfield, Reading, Berkshire, UK, Posts: 1,055	Re: Why do they use mains connectors? The early Pyes, LV20 etc. had another way of disconnecting the mains when the back was removed. They had a fixed mains cable but the back was fitted with two "floating" brass pins which, when the back was in place, completed the mains path (in both "legs"). When the back was removed, the pins came with it and the mains circuit was broken. In order to power the set without the back, pins had to be inserted in the holes in the rear of the chassis - I use 4mm banana plugs!

4th Nov 2010, 1:55 pm	#19
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,927	Re: Why do they use mains connectors? Hi As someone who got the mains lead of a colour TV I was delivering( a fairly new 26" Pye 741 - some things you don't forget) tangled around the car's bumper without my knowledge followed by an almighty CRASH I can only say I'm all in favour! Also nowadays the appropriate lead for the country can be put in the box by the importer. Glyn

4th Nov 2010, 7:20 pm	#20
dseymo1 Retired Dormant Member Join Date: Dec 2007 Location: Shropshire, UK. Posts: 3,051	Re: Why do they use mains connectors? Another factor might have been the ease with which a longer lead could be fitted. The only mains socket in the room might well have been on the other side from the preferred location of the radio. Many users (and some dealers) would have simply twisted the ends of the existing lead onto those of an extension lead, and wrapped with insulating tape, but a re-wireable connector at least offered the opportunity to fit a longer flex. Much easier for bench servicing a set too, when the customer's lead could have been fitted with any of a variety of mains plugs.