Not an exciting photo this evening, but it does represent a good chunk of what I’ve been up to tonight.  I’m trying to get my head around how to modify the selectors on my PAX to provide tie line working.  It seems I need to track down some rather specific spring sets, I’ve got the appropriate relay coils, bases and armatures but I don’t have the right spring sets (or even anything close!)

So if you’ve got a stock of spare GPO 3000 type relays knocking around, I’d be grateful if you could have a look and see if you’ve got anything with the following contacts:

So in total, I need 4*changeover, 1*make and 2*break contacts. The order of the contacts on the springset probably isn’t critical as I can re-map contacts as needed. In an ideal world, I’d be looking for enough contacts to make up 3 relays like this – but I’d settle for anything I can get!

Update: John Bathgate at the Dean Forrest Railway has found me the appropriate spring sets and buffer blocks.  Thanks John!

Not so much a photo today as a bit of research.  I’ve been building aVOIP server so that I can connect my 1950s phone exchanges to the internet and make free phone calls through them to like-minded friends.  I’ve built the box with a view to making it as low power as I can.

Unfortunately because of the requirements of the telephony interface card, it’s not quite as low powered as I’d hoped.

According to the power meter I borrowed of Jonathan, power draw is about 100W during booting, but settles down to a very stable 44W once everything is up and running.  Putting a call through the box pushes that consumption up to about 47W which isn’t bad either.  Plugging some numbers in to http://www.lightbulbs-direct.com/article/energy-saving/ works out that it would cost me £63 a year to run the box permanently – or about a fiver a month.

It wouldn’t be on 24/7 all year (I’d probably switch it off if I went away for a week or something) but even if I did that’s not a huge wodge of cash.

I can probably get the power consumption down a bit further if I can find a PSU that’s a bit smarter with its power management, but I’m not sure I can shave a whole lot off 44W really.

My phone line at home has died, taking my broadband with it.  It appears that I’m not quite organised enough to process the photos at home, bring them in to work and post them – so there may be a bit of a delay while I wait a week for BT to fix it.

ObAmateurPhoneEngineerSpeculation: From the symptoms and testing I’ve done (and me spotting openreach rummaging around in a cabinet just down the road from me) I suspect my line has been rejumpered poorly in the cabinet, I think I’ve got the A leg of my line, and the B leg of someone elses line – possibly they’ve got my B leg as well.

I’m sort of hoping BT will blame me, just so I can see the look on the engineers face when I tell him my phone line comes in behind the 1950s electromechanical phone exchange in the corner of the room – and ask him to give me a hand wheeling it out of the way.

[1] 1000 internet points to those who can spot the reference[2]

[2] without just googling it. Bloody cheats.

My last progress report on the PAX restoration was over a month ago.  I’ve made some significant progress since then – I just haven’t written about it.  Well, I say that.  I’m keeping a paper diary, I just haven’t managed to update here (mumble mumble busy at work etc etc)

So In the last month I have:

• Repaired a couple fo damaged heat coils.  I’m pretty sure these aren’t a repairable part, and while my repair works electrically, I’m not sure it would stand up to the lighting strike they’re supposed to protect it from.  Mind you, I’m not planning on having any external plant hanging off this PAX so that’s probably not an issue.
• I’ve fitted a wooden platform to the base of the PAX, to act as a shelf to hold the batteries, charging equipment and a more accessible connection box for connecting external equipment
• Installed the batteries, with a removable connector to make it easy to isolate the battery supply if I need to
• Fully tested all 4 selectors, I’ve identified two of them as having faults on the called subs side of the circuit.  One doesn’t pass ring current on to the called sub, and the other has a ring trip fault.  Neither passes speech.  This is hopefully just more relays to adjust.
• Desoldered, cleaned up and re-wired a 60 pair “Box Connection” kindly donated by John Bathgate from the DFR
• Desoldered the old 50 pair cable from the tagstrip at the back of the PAX
• Mapped out the strapping on the tagstrip.  Which took ages, as there are 500 connections just for the line circuits (and another 50 or so for as-yet-unidentified-stuff)
• Fanned out, laced, and wired in most of a new 50 pair cable from the box connection to the tagstrip on the pax (I left out the lines with unusual strapping until I understand how they’ve been strapped) – that’s what the photo at the top of the post is of.

I’ve still got a lot of work to go, but I’ve got 30 lines available and ready for phones so far.  I’ve identified 10 line circuits (spread across levels 3 and 5) which are all strapped for various forms of tie line functionality.  This is a bit odd, as from looking at the line circuits only 5 tie lines are fitted.

I really need to get my head around how the tie lines work, but my current working assumption is that it’s currently wired for 5 incoming and 5 outgoing junctions.  There are another 10 lines which have unusual strapping, that I haven’t yet identified (they don’t seem to match anything on the diagram)

That is one page of my strapping map.  There’s another page of it as well.  I’m hoping I can use that, combined with the wiring diagram and a series of train journeys to work out what on earth those last 10 line circuits do!

Oh yes.  And I’m building a PC that I can use to hook my PAX up to the internet.  More news on that when I’ve finished collecting the parts together.

From the October 1935 edition of the POEE Journal

From A Handbook of Telecommunication by Bertram S. Cohen published 1946

From Telephony by Atkinson, 1948 edition

From  Telephony by Atkinson, 1950 edition

I’ve enjoyed working my way through the 30 or so adverts I’ve scanned so far (you can browse the entire collection here) but now that I’ve started looking, I’m going to have to carry on looking!  There must be so much of this material hidden away in books, magazines and journals – overlooked by most people who are more interested in the published articles and the content of the books than the advertising which offset the publishing costs.

Since I first got it, I’ve been trying to work out how to tell when my PAX was built. Initially, I thought it was much earlier than it is.  My first post here describes it as “1930s” which turns out to be wrong.  The initial design of it may be late 1930s, but my example is much later.  As far as I can tell, there were at least 3 generations manufactured:

• A cabinet with a “black crystalline finish” – this is the version described in an article from 1938.  I’m pretty sure there was a 25 line example of this at Ffestiniog when I collected mine.
• A cabinet with a “grey hammered finish” – wired throughout with silk covered wiring (this is the one I’ve got)
• A cabinet with a “grey hammered finish” – wired throughout with PVC covered wiring.  This would be later than mine, and there was certainly an example of this at Ffestiniog.

The company which made it, has had several names, and at least three logos.

• A circle containing the letters ATM, with the company name “Automatic Telephone Manufacturing Company”
• A circle containing the letters ATM, with the company name “Automatic Telephone & Electric Company” (as found on my 50 line PAX, shown above top)
• A circle containing the letters ATE, with the company name “Automatic Telephone & Electric Company” (as found on my 10 line PAX, shown above bottom)

Here’s the timeline my internet research dug up.  Most of the links below are from the same site, but that’s only because there isn’t a huge amount of information online about this company:

• 1911 – Automatic Telephone Manufacturing Company established (From Uk Telephone History and History of ATM)
• 1912 – Automatic Telephone Manufacturing Company established (From A history of Plessey, Information & Publicity Services, PTOSL, Beeston.  This conflicts with the 1911 date claimed elsewhere, but that may be due to a difference in the definition of “established”)
• 1936 – Company changes name to “Automatic Telephone & Electric Company” or AT&E, keeps the ATM roundel in the logo despite the name change (From History of ATM)
• 1938 – AT&E magazine published, describing the first model of my PAX.  The unit is described as having a “Black crystaline finish” – my unit is a gray hammered paint finish so is obviously later  (From Private Automatic Exchange Equipments, A new series of designs)
• 1946 – AT&E advert, showing the same logo (ATM roundel, “Automatic Telephone & Electric Company” text)  as the front of my PAX (From http://www.gracesguide.co.uk/Automatic_Telephone_and_Electric_Co)
• 1950(?) – Another advert, same logo in use (From http://www.flickr.com/photos/36844288@N00/3726593641/)
• 1951 - An extract from an AT&E brochure, also describing the ”Black crystaline finish”
• 1957 – My 10 line PAX has a stamp inside indicating it’s built to “Diagram S202662/Issue 8″ – my copy of ”Diagram S202662/Issue 8″ is dated 1957.  However, this just means it was built *after* the Issue 8 design drawing was released.
• 1961 – AT&E merges with ETL and Plessey (From A history of Plessey and History of ATM - the latter notes that AT&E continued to use the name for a while)

So, based on the paint finish, mine can’t be any earlier than 1951, and based on the company name it can’t be later than “a while” after 1961.  Hmm, that’s not satisfyingly accurate enough.

All those dates and still no hard evidence of when my PAX was built.  It was at this point, I remembered something from a discussion about relay markings.  The 3000 type relays used in my PAXes have markings on the end which tell you useful stuff about any special characteristics the relays have.  Amongst the markings it tells you which company built the relay, and (crucially) when!

This extract from Telephony by J. Atkinson (Volume 1, Page 113) explains the markings:

I felt like a bit of a muppet.  That’s a much easier way to date my PAX and far more accurate than playing “guess when the logo was used”!  So, from looking at the equipment permanently installed in my PAX (rather than the selector cans, which can be removed), I found relays with the following dates:

• 1956,1957 (First 40 line circuits)
• 1960 (Last 10 line circuits.  From the looks of the mounting strip, they’re a later addition)
• 1951, 1957 (Ringing, Tones, Misc relays)

Ignoring the 1960s additional line circuits, and assuming that the 1951 relays were a batch being used up (or spares replaced from old stock) I think it’s reasonable to conclude that my PAX was built in 1957.  So not quite “1930s” as I originally stated, but still, it was built 54 years ago!

If I take a look at the selectors (which are removable, so unreliable for dating purposes as they could be swapped around) I have dates of 1955, 1962, 1965 and 1969.  By fluke, I had arranged the selectors on the shelf in date order!  I also note that the very first selector I got working was the oldest example.

While in a new-found-dating-frenzy, I thought I’d date my 10 line PAX.  This is a little easier to date as it has had less work done to it over the years.  The relays are all dated 1958 or 1959.

With this piece of information, I can deduce that the logo with the ATM roundel was in use from the merger (1936) to some time between 1957 (My 50/7A) and 1959 (My 10/2A) and that the change from silk to PVC wiring also likely occurred at around that time (as my 10/2A is PVC wired)

I spent Saturday building a wheeled platform for my PAX, which should make it easier to work on (and easier to live with!) I was a little bit generous with the amount of tolerance, so there’s a bit of a gap around the PAX but that’s not really a problem.  J came over on Sunday to give me a hand hauling the PAX up onto its trolley:

Now that it’s mobile, I can set about moving the rest of the furniture in the lounge to make space for it. I think the cat will get used to it eventually!

Those are the line relays for my PAX.

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.

(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!