Telephone Exchanges in the UK
(telephone-exchanges.org.uk)129 points by petecooper 16 hours ago
129 points by petecooper 16 hours ago
If anyone is interested in telephone exchange technology at all, I highly recommend checking out the Connections Museum in Seattle. They have multiple eras of electromechanical switching equipment up and running, and a huge collection of cool old phones, teletypes and payphones. They also have a great YouTube channel with very knowledgeable people.
https://www.telcomhistory.org/ConnectionsSeattle.html
https://m.youtube.com/@ConnectionsMuseum
I feel like they're not well known and there's no place like it!
Another excellent museum is the Kodiak Military History Museum at Fort Abercrombie, on Kodiak Island, Alaska.
It has some old working telephone and teletype systems. You can watch the physical switching equipment do its magic. It is truly awesome. The raw speed and accuracy of the mechanical systems is almost unbelievable.
Don't miss https://www.youtube.com/watch?v=kfOzyIib7wU for some young folk urban exploring what turns out to be a still active exchange, full of ancient and modern tech
I know one guy who make something cool with old Telephone and electronic stuff https://this-museum-is-not-obsolete.com/
You can go and play with an old branch exchange, with all the whistles and er, bells at "This Museum is (not) Obsolete". Run by Sam from Look Mum No Computer. If you're ever near Ramsgate in the UK.
The Avoncroft museum of buildings in Bromsgrove, near Birmingham, UK, is worth a visit. They have a bunch of old telephone boxes all working and hooked up to an exchange they have on site. I spent like an hour talking to the guy in there about it all, pretty fascinating.
https://avoncroft.org.uk/avoncrofts-work/special-collections
This is an impressive feat of cataloguing!
Considering the telecom system is at the bedrock of almost all modern technologies, it really doesn't get enough love or attention in the public mind.
The dull derelict-looking, and often graffitied, buildings that house the system doesn't reflect just how cool the infrastructure is.
My physics teacher in the 1980s (sadly RIP a few years ago[1]) told me that the location of telephone exchanges was a UK state secret. The theory was that the Russians would nuke them destroying the country's ability to communicate, but as their location was a secret that outcome could be prevented. 40+ years on, I wonder if any of that was actually true?
[1] https://johnchess.blogspot.com/2019/11/david-welch-1945-2019...
> the location of telephone exchanges was a UK state secret
I found myself wondering whether the locations of electricty substations powering critical infrastructure might count as "secret", for instance the three[0] substations that power Heathrow Airport.
Obviously one of them isn't secret any more more, having gone up in flames rather spectacularly on 21 March 2025.
[0] "Heathrow relies on three electricity substations" https://www.bbc.com/news/articles/c6283577llqo
In hindsight, that does seem a little ridiculous; yet it was indeed the thinking. One could see where the exchanges were by simple dint of visiting a place. Soviet spies would just have had to walk around a bit.
Of course, nuclear weapons wouldn't even have had to specifically target exchanges in order to disrupt electronic communications as they already were by the 1980s.
It was amusing to learn a decade ago that the U.S.S.R. military had far more complete maps of many parts of the U.K. than Ordnance Survey published. Apparently down to Soviet spies just walking around a bit, playing tourist.
The dullness is eerily consistent. Even in the age of privatisation, when everything is a brand, these buildings are devoid of markings. So it might well be true, we just stopped worrying about it once the cold war was officially over (once we realized the Russians already knew everything they needed anyway).
>As our [1978] trial started, witness after witness from security sites tried to claim that openly published information was in fact secret. In a typical interchange, one Sigint unit chief was shown a road sign outside his base:
> Q: Is that the name of your unit?
> A: I cannot answer that question, that is a secret.
> Q: Is that the board which passers-by on the main road see outside your unit’s base?
> A: Yes.
> Q: Read it out to the jury, please.
> A: I cannot do that. It is a secret.
>Official panic set in. The foreign secretary who GCHQ had bullied into having us accused of spying wrote that “almost any accommodation is to be preferred” to allowing our trial to continue. A Ministry of Defense report in September 1978, now released, disclosed that the “prosecuting counsel has come to the view that there have been so many published references to the information Campbell has acquired and the conclusions he has drawn from it that the chances of success with [the collection charge] are not good.”
>My lawyer overheard the exasperated prosecutor saying that he would allow the government to continue with the espionage charge against me “over [his] dead body.” The judge, a no-nonsense Welsh lawyer, was also fed up with the secrecy pantomime. He demanded the government scrap the espionage charges. They did.
GCHQ and Me, My Life Unmasking British Eavesdroppers -- Duncan Campbell
https://theintercept.com/2015/08/03/life-unmasking-british-e...
Sort of, yes. https://en.wikipedia.org/wiki/BT_Tower#Secrecy
Two more examples of exchanges that were kept secret:
I used to live pretty much opposite the village exchange. It was just a very boring and nondescript little building, backed up by the picture on that website. I bet it was much more interesting inside though
Our old countries (and their tech) building on top of old.
Developing countries have less of a hassle with implementing something based on state of the art.
Lots of hassles with getting new phone lines, new power lines et al in the UK based on old agreements and a nationalised infrastructure. Please stop digging up roads and everything for arbitrary telecoms companies based on some deregulation, some collaboration please :-)
someone from the local gas company told me that the reason the utilites don't work together is that they can't because of rules - electric and gas need to be kept separate for safety, and the surrounding soil means water leaks can be absorbed away from other utilities' pipework. I didn't dig any deeper
Like most things that's half true.
It's true you don't want a telecom worker laying a gas pipe, however you can coordinate this stuff if you want to. Typically the deepest utility works first then backfills just to the level of the next utility and so forth. However timing is critical, the second utility must be ready to work as soon as the first is done and so on.
The biggest reasons they don't is mostly (in this order)
-They can't time their work to be at the same time as 3 other utilities.
-They can't work out cost and liability sharing, if the last utility to work does the reinstatement and takes liability for it then the telecom company will always pay while electric typically won't pay anything as it's in the middle. The legal demarcation between utilities is also much less clearly defined.
-Contractors typically do all work, not actual utilities and it's in their best interests to dig the road up five times (one for each utility) rather than just once. The same goes for everyone else who gets paid when the road is opened; including, often, the local government (for permits).
I feel there's a generation of Brits burned the wave of random telecoms companies digging up major roads for years for cable, only for the results to be pretty much useless by the time it's done as ADSL and existing POTS lines could do pretty much the same thing without any more digging.
The words "Diamond Cable" still fill me with dread to this day. They dug up half our village to then offer no service.
I visited an exchange back in 2009, when Local loop unbundling (LLU) on ADSL was big, and fibre was limited to large business and datacentres. The huge generator was probably more interesting than the racks of concentrators. I'm not sure how much battery back-up power time the new PON systems have, I assume less than a generator backed system.
In a similar vein, but for the US: https://www.co-buildings.com/ (And a shoutout to https://long-lines.com/)
I recall there was a voting system by BT circa 2002 to get your local exchange upgraded to "broadband" (i.e. not just 56k dialup) if it wasn't already.
Interesting to see Kinghorn in the database (01592-89) because I toured the exchange as a child sometime in the late 1970s before it was brought into service (my Dad knew a bloke who worked for GEC). iirc it was a TXE4 system then, or at least of that generation. Building in a very poor state of repair now. Probably hasn't been painted since 1979!
Really, its own internet system before the internet. Massive load of calls. The routing has to be correct. I never understood it before working in telecom, but phones numbers are unique... for routing, like IP-addresses. And it could never go "down". In the 80s it was all digial too (Ericsson switches) and had to be real-time.
Before modern digital electronics, telephone numbers were literal routes - when the turned dial on your phone ran back to zero, a corresponding 10-pole motorised rotary switch at the exchange turned and connected you to one of 10 lines. This connected you to another such rotary switch for the next digit, until eventually you were connected to the final destination. The ingenious Strowger exchange.
And when there was a bug in that complex and vast routing system somewhere, it was completely unfixable. Not without million-dollar hardware replacements at least.
It's really surprising to me how little uptake 2600 ultimately ended up having.
Also, every phone had its own physical circuit to the exchange, leading to things like this: https://i.redd.it/ugvoc90k4q5a1.jpg
Generally yes and even today, if you've got a twisted pair, it's that down to the exchange. Though party lines were also a thing a very long time ago.
There were also specialist circuits (e.g. EPS) where you had a physical line from end to end (with a couple of amps along the way on longer runs).
Crazy. There is also the https://en.wikipedia.org/wiki/Old_Stockholm_telephone_tower#...
Invented by a paranoid undertaker out of business interest, apparently:
"Strowger, an undertaker, was motivated to invent an automatic telephone exchange after becoming convinced that the manual telephone exchange operators were deliberately interfering with his calls, leading to loss of business."
I wonder if the phone company was actually out to get him!
> Really, its own internet system before the internet. ... for routing, like IP-addresses.
There's a great video from Connections Museum (mentioned further up the thread) where they're going through the operation of, I want to say, one of those crossbar switches? And they start using terminology like "routing table", "longest-prefix matching", and "default route", which all sounds well and good, until you realize they're talking about systems that existed decades before the Internet or even ARPANET, all electromechanical... Dope stuff. Cool to see how things rhyme even as they change.
Combination of Ericsson and GEC/Plessey/BT "System X" (see https://en.wikipedia.org/wiki/System_X_(telephony)). Erisson AXE10 was known as "System Y" in the UK and a hedge against buying exclusively System X equipment.
The site won't let me past the initial verification page in either Firefox or Vanadium.
Is their content really so sensitive that it must be "protected" to such a degree?
My dad worked at BT and used to take me to different exchanges at the weekend normally on Saturday mornings. I guess he claimed a day in lieu for working a couple of hours and then we went for lunch or pottered around the shops. In there were all sorts of interesting things. Piles of discarded electronics of various eras. Several computers and terminals for connecting to mainframe systems. I remember a Sinclair QL and Amstrad PCWs I think. He would let me play around with the terminals, no idea what OS was on there maybe VAX or VMS, use the printers and Microdrives. I was really interested in all that stuff as a kid but didn't really have anyone to learn from as my dad was more of a lineman, having started in the Royal Signals. Fun times!