Wireless Set No. 52 Canadian - Project

[David Dunlop]

While rummaging through some more wireless bits boxes on the weekend, I rediscovered an old project package I had abandoned umpteen odd years ago, Trying to put together the really good parts from several Key & Plug Assemblies No. 9 Canadian, to make a good one for one of my 19-Sets. I think I stumbled across a very good assembly at a local sale and work on the project halted.

As it turns out, one of these Key and Plug Assemblies is needed for the 52-Set, and since I cannot do any soldering until my new soldering station arrives, I decided to reactivate the work needed and put a Key & Plug Assembly together for the 52-Set.

The project was simple enough, involving the transfer of the plug and cord assembly (in good condition) from a scruffy unit somebody had cut the leg straps from, to a very good unit somebody had cut the plug and cord from.

There are only two things that are a bit tricky about the work needed to be done: the two terminals on the positive and negative cord leads are crimped to the leads AFTER the cord is fed through the grommeted opening in the key base plate at the factory and they are too wide to slip back through the grommet as is, and secondly, there is an anti-strain loop woven into the cotton cord loom that slips over a J-Post Bracket at the back of the key bar assembly, just inside the case, This cotton loom is now some 60+ years old and is often not up to liking a lot of pulling and tugging, without breaking.

Step one is to remove the two terminal screws for the positive and negative leads. Make note the negative (earth) lead is the front most one. It has green cord wrapped at the base of its ring terminal and a green tracer woven into its loom. The line directly behind it is the positive one, with a red cord wound at its terminal lug and a red tracer woven into its loom.

Once you have removed the two leads from their terminals, remove the terminal screw on the back of the J-Post. It is only there to secure the anti-strain loop that has been slipped over the post. You will have to feed about one more inch of the plug cord into the key assembly at this point to give yourself enough loose cord for slipping the anti-strain loop off the J-Post. Once it is free, you just have to deal with the two terminal ring lugs.

The best way to remove the two leads is to hold a ring terminal with a pair of pliers, on one side of the lug, about one third of the way across the ring, Then take another pair of pliers directly across from the first and GENTLY and SLOWLY bend the ring to form a gradual, near 90 degree bend. You just want the diameter of the ring to have reduced enough to slide out through the metal grommet. Do the same to both ring terminals and you should then be able to remove the plug cord from the key assembly. Best to do it strain loop first and then one electrical lead at a time.

Reverse the process into the good key assembly. Insert enough cord that you can easily slip the anti-strain loop over the new J-Post and then gently snug it back. To reflatten the two ring terminals, I use a pair of needle nose pliers that have a smooth inner face to the jaws down near the jaw pivot point. Or, I sneak a pair of Debbie’s jewellery pliers that have smooth faces to do the job.

A couple of other points on these Key & Plug Assemblies. I have seen them with and without the bakelite guard fitted to the key bar, under the bakelite knob. I am not sure if this is just a case of these guards sometimes ‘disappear’, or if it reflects a change in production, with early morse keys lacking the guard and it being added later. No big deal if you never plan to use the key, If you do plan to use the key for CW work on a restored wireless set, I highly recommend you find a guard and install it.

Ever noticed the funny looking bakelite finger guard surrounding the morse key socket on the Mk III 19-Set? It is usually not there on the Mk II Set, which normally has either nothing, or a simple flat rectangular bakelite plate around the socket.

When you are working CW on a wireless set, the Send and Receive functions are controlled by the key plug. Fully inserting the plug places the set into transmit mode, pulling the plug half out of the socket places the wireless into receive mode. In Receive mode, one half of the brass plug assembly sits exposed outside the front panel of the set. If the wireless operator is in a hurry to transmit and pushes the plug back in with his fat fingers in the way, he will find full transmit High Tension power arcing into himself very quickly. Hence the development and installation of the finger guards. And the guards are great, but not perfect. The one on the Morse Key Bar and the knob will only protect you for the first 8 Amps. After that you are on your own.

Wonder how many wireless operators had their key strapped to their thigh first thing in the morning and spilled their cup of tea on their lap? Be more than their Rice Krispies going ‘Snap, Crackle and Pop’.

Hope this wan't too long winded.



David

[Chris Suslowicz]

Ah, you're fitting the cable backwards!

Replacement cables would be supplied with the appropriate tags on both ends, the key end would be attached first, and the cable fed through the grommet, after which the jack plug would be fitted to the free end. Workshops (ant telephone exchanges) had a hand-cranked jig to assist in screwing the jack plug on to the (ready made) cable, after which the crimped-on terminals would be fixed to the plug connections and the plastic cover screwed home.

I'd like one of those jigs, as I have replacement switchboard cables (in Chinese Red only, so far) to restore my Switchboard UC and its severely moth-eaten cables with.

Original British keys used the No.10 plug, which provided adequate finger protection. The Canadian keys had a more exposed 'hot' end, and the set was fitted with a plastic guard to reduce the risk of a 'belt' from the buffer stage HT (250 volts or thereabouts). I can't remember what the American keys used.

'Ham' modifications using commonly available jack plugs are a recipe for disaster if used by the unwary: Post Office style jacks with exposed screws (and the tail end of the brass body) are a hazard, and I hate to think of what the modern "all metal" screened plug would do to the user!

Chris.

[David Dunlop]

Hi Chris.

I’d prefer ‘Reverse Engineered’ rather than ‘backwards’.

Thanks for the assembly background. I didn’t realize a special tool was used to fit the plug end assembly, but do recall that end looked odd in some way in which the plug was fitted over the cable. I was concerned the old loom might split or tear if I played with it too much, so decided to leave it alone and go the back door route.

Cheers,

David

[David Dunlop]

Not much work done on the project this past week beyond restocking soldering supplies and getting familiar with the new soldering station.

However, the attached item arrived in the Mail on Wednesday, compliments of Bruce Parker. It has tidied up quite well and the few missing bits should be easy enough to track down. It is now penciled into the project right after I finish getting the two receivers up and running.

The real gem about this Coil, Aerial Tuning unit is that inside, it is still the original, pristine factory No. 2 Brown paint. Not faded at all from exposure to light of any kind for 74 years. It will definitely be the item scanned in for matching when the time comes for painting.

I thought I would now also post another photo of the project overall to date. Had to transfer in another section of wireless bench from the workshop to accommodate everything, but I had planned for that some years back when designing the Wireless Table setup. Top shelf holds the Main Set Receiver and Coil, Aerial Tuning. The lower shelf the Remote Receiver and Case, Remote Supply Unit, Accessories and spare parts receiver. The starting point Aerial Bag and F-Rods is still on the wall. The tea towel on the Main Set Receiver is not original to the 52-Set. It's 'Cat Proofing', held down by a 2-inch binder full of 52-Set literature/reference manuals.

So, some progress is being made after all.

David

[David Dunlop]

Finally finished with the reconnection of the AC Line Cord to the chassis of the ZE-11 Remote Supply. In the attached photo you can see one lead just left of centre, curving past a hex nut and up to a terminal on a toggle switch, and just left of that, the second longer lead arcing up towards the camera and then on down to a terminal on the AC Selector Socket.

Having done that, I plugged in the supply and turned the electrons free. Low tension came in on target at +12V AC, but the high tension output was only +15V DC instead of the anticipated +150V DC. The input voltages to the OZ4 checked out at +201 V AC, so the transformer is OK, Downstream of the OZ4 checked out with the correct amount of resistance, so back to retest the OZ4. Bummer! It came in at barely 8% effective. Can’t really complain. It is probably the original 1943 Marconi OZ4.

Now to track down a good OZ4 and try again.


David

[David Dunlop]

Well, a minty new OZ4 has now been installed in the supply, and even a diode based replacement constructed...just in case. Both work beautifully in another piece of equipment. Not so much in this supply. Sigh.

I should qualify that. They are working just fine but something downstream in the circuit has now reared its head to say hello with a grin! The current suspect is the C25A/B capacitor can that covers both sides of the filter choke. Seems more disassembly and testing is ahead.

This is almost as exciting as taking a CMP apart with a 1/4-inch socket set!

David

[Chris Suslowicz]

You'll almost certainly find that C25 is no longer a capacitor and needs re-forming or replacing. Old electrolytic caps lose the insulating layer on the plates/foil over time if not used, and act as resistors instead. If power is applied they can explode due to a build up of pressure caused by electrolysis.

There are ways round this, using a variable voltage supply to bring it back to life slowly, or a "proper" re-forming unit that applies pulsed DC in an attempt to re-form the aluminium oxide insulating layer.

Chris.