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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 17th Jul 2014, 4:13 pm   #1
Tyso_Bl
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Default Murphy B40D Mains connector and switch

What are the standard solutions to the B40 mains connector problem, have a look at this, no doubt it must have worked at some point, note the large loudspeaker switch, from the colour of the wiring it might have done duty as the power switch at one time. The switch is unservicable now. There isn't a hardwired mains earth either, I assume it may have been done via the connector shell.

I'm not one that cares for originality over safety, so do we wire up a standard IEC chassis plug and some sort of switch (will look in parts/junk box), or hardwire a mains lead either through the front or back with a separate isolation switch to attach to the bench or cabinet?
I'd prefer to go for a reversible solution.
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Old 17th Jul 2014, 5:08 pm   #2
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Default Re: Murphy B40D Mains connector and switch

I have a connector that will match the original chassis socket so that you can make a real mains lead for it.
They do not fit through the 25mm slot at the post office I am afraid.
They do use the shell for an earth.
You can send a PM if you are interested.
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Old 18th Jul 2014, 12:40 am   #3
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Default Re: Murphy B40D Mains connector and switch

Thank you for the offer Refugee, it'll give me an option to keep it original.
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Old 18th Jul 2014, 7:09 am   #4
G4XWDJim
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Default Re: Murphy B40D Mains connector and switch

Here are pictures of the Plessey MKIV mains socket on my signal generator. It fits in the same size hole as the two pin B40 socket. The Racal RA17 also uses this three pin plug socket arrangement as do many other pieces of similar vintage equipment so the plugs should be easy to find and will fit straight in to your B40.

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Old 18th Jul 2014, 2:03 pm   #5
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Default Re: Murphy B40D Mains connector and switch

Switches of the type used in the B40 have an unfortunate and rather treacherous habit whereby they will occasionally apparently mechanically switch off with a satisfyingly clunky action but leave the roller contact in place and circuit live- perhaps the previous owner came across this and replaced it?
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Old 18th Jul 2014, 3:57 pm   #6
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Default Re: Murphy B40D Mains connector and switch

I like the idea of Jim's Plessey MkIV connectors, with the three pins it would sort the eathing situation, I'll look out for some and make sure I don't do anything ireversible.

The switches look well built, and as turretslug has pointed out don't fail safe, the speaker dummy load switch at the back of this radio is exhibiting exactly this sort of behavior.
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Old 18th Jul 2014, 4:15 pm   #7
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Default Re: Murphy B40D Mains connector and switch

If you're after a source of Plessey Mk.4 connectors it's worth checking "Electrojumble".

http://www.electrojumble.org/

[No connection with them except that they've been a good source of the obscure both-pins-and-sockets-in-each-connector Plessey Mk.7 connectors I needed for some ex-mil Clansman gear]
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Old 18th Jul 2014, 4:47 pm   #8
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Default Re: Murphy B40D Mains connector and switch

The Plessey connectors are a safety hazard in that all of the pins are the same length. In any mains connector, the earth conductor must make first and break last - usually achieved with a longer earth pin, as in a 13A plug.

I can fully appreciate a need to preserve originality - but I would recommend taping securely the locking ring of these connectors and breaking the circuit elsewhere.

Using this connector as designed on a piece of equipment with an earth fault (or even a mains filter, if conditions are damp) could result in a shock hazard or worse - damaged equipment if it is dropped....

Leon.
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Old 19th Jul 2014, 12:42 am   #9
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Default Re: Murphy B40D Mains connector and switch

Quote:
Originally Posted by Leon Crampin View Post
The Plessey connectors are a safety hazard in that all of the pins are the same length.
<snip>
I can fully appreciate a need to preserve originality
Thanks for bringing this to my attention, I wouldn't have noticed till I'd got one. I may have to hardwire it with an external switch, I'm not too bothered about originality, if these things were still in service they would have been modified and upgraded anyway, what's happening to it now is another chapter in its life, better that than scrap metal. I prefer a safe functioning radio to one that may be original but unsafe or nor function as well as it could.
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Old 19th Jul 2014, 12:34 pm   #10
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Default Re: Murphy B40D Mains connector and switch

There are a scattering of small, circular mount 3-pole connectors with leading earth but I'm not certain that many of the commonly available ones would comply with current legislation/recommendations. Two types of mains inlet connector that would fit the existing hole but would require supplementary c.3mm fastening holes are the Souriau mains connector (mentioned previously on the forum in connection (!) with the B40, a forum search should bring it to light) and the IEC C5/6 type. I've a few of both types, I'd be happy to dispatch a pair of either but postage would probably be more than they can be purchased and delivered for on some sites. (How do they do that?)

I also have the odd Plessey Mk4 3-pin panel plug I'd be happy to pass on (with Refugee's caveat)- it's a connector I remove and replace on sight! (In the days when legislators were busily mandating safety considerations such as leading earth, inherently bonded shells and fixed, unambiguous keying/polarisation for civilian-use mains connectors, HM Servicemen were being expected to work with something that fell woefully short on all three counts- something I find rather offensive . I can hear pompous and duplicitous waffle about how "our armed forces have always had the best equipment money can buy... blah, blah"!)

Anyway, (takes deep breath, puts soap-box away) good luck with re-vitalising the B40, it's certainly a distinctive and worthy bit of kit.
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Old 19th Jul 2014, 2:05 pm   #11
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Default Re: Murphy B40D Mains connector and switch

@turretslug, somehow I missed the Sourari relataed posts, interesting, the discussion so far has helped me make my mind up. The plan now is to fit a short captive hardwired computer IEC plug, to mate with a standard lead with fitted socket. So thats the plug n socket covered. Things yet to decide, front or back of radio, and what to do about the switch, if I can find something that looks ok I'll fit one on the front panel, if not I'll fit one inline with the captive lead.

The b40 is distinctive, I've not yet researched if there is a matching TX to accompany it, but if there is....

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Old 23rd Sep 2014, 9:19 pm   #12
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Default Re: Murphy B40D Mains connector and switch

Two way mains plessy/painton socket are original fitted tot B40 B41 62B.

Original mains wire is black pvc isolated flat braided wire. Two isolated conductors: live and neutral. The braid is used for earth.

I use a piece of soldered on copper foil (earthshield for 10kV 3 phase cable) to attach earth (if the 3 conductor wire is used) at the shell (pressed with conical ring/washer.

These receivers have a ground screw socket just below the headphone sockets. Thats a good alternative. Just buy blank braided earth/chassis/massa car wire.

Electrojumble is very ok.! I did some business with them buying all sorts of plessey plugs and sockets. And so making the correct cables for antenna and mains. And restoring receivers on that part.

Please pay attention to this: Bear in mind that the inner bakelite parts have 6 ways of position (angle) These positions should also match the plug and socket. Not only the aluminium shell should fit. So be carefull with which position makes the plug and socket match mechanically. If the conductors are wrong positioned then you can start a fire...

The soldering contacts should be shrinksleeved to gain as much as possible isolation.

I assemble these cables and sockets for my colleague murphy collectors. just by a very good closeup macrophoto.

Hoping to have added extra usefull info.

If interested see a part of my collection:

http://www.gloeidraad.nl/radioforum/index.php?id=146815

best regards Qwenix

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Old 23rd Sep 2014, 9:33 pm   #13
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Default Re: Murphy B40D Mains connector and switch

There is a transmittersystem which could accompany the b40 or even the cas receiver Its the type 618/H/L.

Consisting of type 618 cas and power unit. Lots of info i do have here in my
BR 333 handbook and lots of info you can get at HMS Collingwood radar and communication museum: lots of info but you have to like the search.

http://www.rnmuseumradarandcommunications2006.org.uk/
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Old 26th Sep 2014, 3:24 pm   #14
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Default Re: Murphy B40D Mains connector and switch

An update, I've solved the issue of the mains connector and switch to my satisfaction, for the record we now have a IEC socket on the front chassis plate that also holds the switches, filing a selected plug allows it to fit through the large hole in the front panel without butchering the panel. Junk box scavenging has produced two non matching British made switches to deal with the mains and internal speaker.
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Old 26th Sep 2014, 6:13 pm   #15
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Default Re: Murphy B40D Mains connector and switch

I think that changing these sockets into iec parts lies in the thought that the original plessey sockets and plugs are unsafe. I do things the opposite way e.g. a faz outfit ssb had been modified with a iec connector. I reversed it into as much as possible original. Ive never experienced a burn out plessey connector/ plug or blown fuse due to short circuit. Fuses do protect the receiver against damage and if a good earth is supplied than what could go wrong. So i say to my fellow collectors in holland to keep it as original possible. Most of the modification on old receiving measuring transmitting equipment are executed because the original mains leads or other antenna leads are lost . Soldering spots on plessey sockets and plugs should be shrink sleeved rather difficult but i always do. And of course use a good magnifier to examine thd soldering spots and after closing the plug/socket always measure resistance between the conductors.
Best regards, qwenix
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