Since my last post, I’ve been giving the other selectors I’ve got a bit of an overhaul. Cleaning, oiling and adjusting the mechanism, tweaking relay contacts etc. I now have 3 working selectors – which means the exchange can now handle 3 simultaneous calls! Which is still a bit daft with just me in the house, I’d need 5 people to come and visit to bring al three selectors into use. Mind you, that’s no more daft than having the thing in my front room in the first place:
I spent last night with the 3rd and 4th selectors on the bench, using number 3 as a reference I replaced the wipers on number 4. This is quite possibly the most fiddly thing I’ve done on this exchange so far. I’m sure it’s really straight forward if you’ve been on all the appropriate GPO training courses, but if you’re just trying to figure it out on your own it’s not easy! Selector 4 is the one furthest from the camera in this picture:
So, selector 4 now has new wipers, and steps cleanly mechanically. Unfortunately there seems to be an electrical fault with it. It will step vertically on the test stand, but it won’t step horizontally. Thankfully the rotary magnet seems to still be alive (at least, it meters at 50Ω, which is about right) as changing those out looks like a nightmare. There is a good solid connection to battery on one side of it (it’s energised by connecting the other side to earth) but it doesn’t even attempt to operate.
My other initial thought was the N springs, but they all appear to operate correctly.
So, it’s more time spent pouring over the circuit diagram for me then!
I promised myself that I wouldn’t do any of the fun jobs on my PAX (eg replacing the ringing vibrator contacts, fault finding selector position 2 or setting up a second selector) until I’d given it a bit of a clean. So, out came the soapy water and mild detergent along with a nice new non-stick-safe washing up sponge…
That’s them up there, by the time I finished.
Some bits of the PAX (notably the inside of the base) are now almost a completely different colour, and the whole thing looks a bit less like I’ve just dug it out of a shed at a steam railway. I’m hoping it smells a little less musty, but won’t really know until I next leave the house.
Cleaning has shown up some surface staining which won’t come off all that easily (it seems to be spilt varnish or something) and several places which are beginning to develop rust patches – but I’ll get to them all in good time.
Yesterday, Ian and I drove from Bristol to Porthmaddog in Wales to the Ffestiniog Railway to collect a small(ish) telephone exchange or PAX (Private Automatic Exchange) The railway were having a bit of a clearout, so while we were there we piled a load more stuff in the van. Probably more than we should have really!
(The big grey box at the bottom of the van is the PAX)
It was a long drive home, so we didn’t unload the van immediately. Instead Ian came over before work this morning to help me get the PAX out of the van. After a lot of effort, we managed to get it into my lounge, where I can work on it until I no longer need to get to the back of it. Once it’s all working, I’ll move it into an alcove where it’s less obtrusive and disguise it by putting a pot plant on top of it or something.
It’s a 50 line automatic exchange with 7 connect circuits (although I’ve only got enough selectors to populate 4 of them) once fully populated it can support up to 7 conversations at once. It’s equipped with tie-line circuitry so I can connect it to other exchanges. I’m hoping to use these to hook it up to the internet so that other people with similar exchanges can dial into it.
The selectors are all 2000 type strowger selectors, which are familiar to me from the exchanges I help to look after at the Dean Forest Railway. I’ve spent the evening fiddling with it, checking things over and cleaning relay contacts. After a thorough visual inspection I bravely hooked up a set of batteries and jacked in the best of the selectors. With very little fettling, it works! So I’m already 25% of the way there!
All the phone numbers are 2 digit numbers, in the ranges 20-29, 30-39, 40-49, 50-59, 60-69. When you dial the first digit, the selector steps up that number of positions. When you dial the second digit, it steps in that number of positions. In the video below, you can see me dialing 68 and see the selector step up 6 places, then in 8 places.
I just love the noise these exchanges make! I can’t wait to sort out the rest of it!
As some of you know, I’m designing and building a telephone exchange from scratch. I’m aiming to use components which would have been available in the 1950s (with the exception of a bucket full of silicon diodes because I can’t find enough metal rectifiers or appropriate relays to do the job)
While all the techniques I’m using would be understood by a telephone engineer of the time, I can’t say they’d all be familiar as some of my circuit design is a little “non standard” – some bits of this exchange design would no doubt raise an eyebrow or two!
The exchange will have 20 lines in total, numbered 20-39 (In the photos, you’ll see them numbered “21-20, 31-30″ which is because “0″ is a “10″ in pulse dialling terms. If you’re laying out the lines in the order that the final selector would connect to them they go: x1,x2,x3…x8,x9,x0)
So, I’ve spent the last week and a half’s worth of evenings, making a start on the wiring the multiple. The multiple connects each line circuit to each of the 4 uniselectors (two are linefinders, used to detect someone wanting to make a call. The other two are final selectors used to route that call to another phone.)
If I’ve done my sums correctly, there are 298 wires, 358 soldered connections, 120 wire wrap connections, 40 diodes and 4 uniselectors on this frame. To connect it to the rest of the rack, I think I’ve got another 60 wire wrap connections and 100 soldered connections to connect the line circuits, then at least another 30 soldered connections to connect it to the control circuits (although that’s a bit vague as I haven’t quite finished designing them yet)
If you haven’t dozed off by now, you’ll notice that in the picture above you can see a Van Der Graaff Generator which is awaiting repair (I really must have another look for a source of natural latex straps) yet another telephone and a box of Atari ST games.
Now that I’ve built the multiple, the next step is to put it on the rack, and then turn my attention to the ringing machine (a wonderful combination of electric motors, tone wheels and cams which generates all the tones and ringing current required for a telephone exchange) – oh, and of course I need to finish the rest of the design.
Then again, it’s taken me 18 months to get this far. There’s no rush!
It was the first THG swapmeet of the year today (pretty much a car-boot sale, but for telephones) – I overslept, and had to leave the house in a bit of a rush, so didn’t take with me everything I was planning to (most importantly, I forgot to take a pocket full of small change – so made a bit of a pest of myself paying for small value items with notes – oops!)
I had a quick jaunt up the M5 to Cheltenham where I met up with Ian in a layby, transferred a couple of boxes of junk interesting telecomunications equipment into the boot of his car and then set off to Avoncroft.
We stopped off briefly at a “real” car boot sale on the way to see if there was anything worth having. There wasn’t. Just the usual mountain of baby clothes, pirate DVDs and nasty cheap electrical goods. Oh, and a stall full of really rather dubious looking home made abstract “art”. Then it was onwards to Avoncroft!
Most of the morning was spent rummaging through boxes unearthing hidden gems and chatting to loads of lovely telephone people. I finally managed to dispose of two fruit boxes full of junk from my front room* – mostly by giving it away to anyone who expressed an interest in any of it. It’s taken almost a year to shift that lot.
After lunch we went to have a look around the Avoncroft collection of telephone kiosks, and managed to swing a tour of their mobile TXE2 electronic exchange. The TXE exchanges were built to bridge the gap between Strowger/UAX exchanges and SystemX. There weren’t as many built as there were Strowger/SystemX exchanges and there aren’t that many TXEs left working, it’s possible that the one at Avoncroft is the only one in fully working condition. (Unless there’s one in the hands of a private collector that I don’t know about)
This is part of it:
Unfortunately, I can’t remember which part. It looks like a jumper or strapping bank though. I took the photo mostly because I thought it was pretty.
Then we had a very interesting talk/demonstration from John Mulrane about how to polish and restore Bakelite. There’s a bit more to it than I had previously thought, but now I want to buy a buffing machine so I can really clean up some of my phones. John was getting marvellous results from his!
Then it was back in the car, back to Cheltenham to transfer my goodies from Ians car back in to mine, then home to Bristol. I’ve unloaded the car, fed the cat, and managed to get an hours worth of weeding done in the garden to boot. All in all, a very enjoyable and productive day.
* I might have filled the gap with the new stuff I brought home, but I’ve traded stuff I don’t want for stuff I do want – which is good! Honest!
I spent another day at the railway today, we jointed another 50 pair cabinet and prepared another cabinet for jointing (once we run in another cable) There was a “Branch line experience day” running as well, and they were pottering up and down the line with Sapper (pictured above). Sapper is a recently rebuilt 0-6-0 Saddle tank who has come to us for a bit of a shakedown.
As well as all the physical stuff, Ian and I spent a bit of time fiddling with our Asterisk server and got it talking to the internet. We can now connect to it from home, and make phone calls through the UAX13 exchange!
Your Challenge this week is to take a photo of somebody enjoying one of their hobbies or pastimes.
The hobby could be absolutely anything, and the “somebody” could be you!
So, here’s me, building a relay set (took bloody ages to capture the whisp of smoke from the soldering iron!)
This can will be part of the system installed in a signal box at the railway called a “concentrator” – it’s a bit like a specialised manual telephone exchange which allows the signalman in the box to talk to trains stopped at signals. The special bit is that it’s got facilities to prevent the signalman accidentally talking to the wrong person (don’t want to tell the wrong train it’s safe to go!)
There’s no PCB, so all the wiring is made point-to-point with jumper wire. Very fiddly to build, but remarkably easy to debug and maintain. No semiconductors in this circuit at all either!
I was taking some photos of phones and stuff this afternoon, and Penny decided she wanted to join in. As ever, her joining in involved wandering into shot, lying down and licking her bits.
In phone exchange news – it’s all working! I can make calls through my ATE 10 line PAX. Hurrah! Video will follow just as s0on as I manage to find my youtube password.
This is why I haven’t been taking photos or updating my blog this month.
What you are looking at, is the beginning of the telephone exchange I’m designing and building from old GPO components and circuit techniques. I’m designing it from scratch, picking and choosing circuit elements from various telephone exchange designs from the 1930s-50s.
Tonight, I managed to build the first two line circuits (there are enough relays in the image above for four line circuits, but better to start small!) After a little bit of debugging (the connection tabs on the back of those relays are really confusing!) all the bits of wire have the voltages I’m expecting on them! Yay!
Some of my prototyping methods are a bit vintage as well. These are copper coated nails, which are used to make an impromptu wirewrap board. This particular bit of prototyping is the subs-multiple.
The stuff I’ve built doesn’t really do much at the moment (apart from click a bit when you pick up a phone) and the next stage is to build the linefinder. That bit is much more interesting as it spins round and makes nice raspberry noises.
