What needs fixing on the Telephone Exchange? - Telephone Tuesdays

[@davecharles7040]

Be aware of the tape drives in the call forwarding units. I used to repair faulty units in the North London BT ARC (Area Repair Centre) based in Winchmore Hill TE. The drives had a history of "eating" tapes. The mechanisms used to fail to take up the tape or slip on the play roller causing the tape to play slow and stick on the roller thus chewing the tapes. Only use copies. Don't use your origional copies as they may get damaged.

[@ShellAndy]

I worked in the Bristol ARC at Backwell on a similar range of goodies. Good times!

[@Wenlocktvdx]

Call diversion bit Telstra when introduced in the 80s. Two customers had diverted to each other and the first incoming call ping-ponged until all the lines were tied up and both exchanges crashed

[@shaitshait123]

i remember when i was a teenager i dismantled an internal telephone excange in an old paper factory in telmark norway, i did not know what it was at the time i just thougt it was so cool and i felt it was a shame to throw it all away it was so old that there also were batteries maybe for running in emergencies or someting and the batteries were made of thick glass so you could see the lead and acid inside, so cool to begin understanding how there things work and you guys finding it out. I still feel like the whole thing should have been taken care of and not thrown away, i still have one of the batteries and a couple of the selectors.

[@cambridgemart2075]

A lot of the old glass cells were NiFe, nickel iron, with a potassium hydroxide electrolyte

[@mickcoleman5396]

The P in P wire does stand for Private (yes there was also private wires as a separate product), if a selector steps onto an outlet and the p wire is active (connected to earth) this means that outlet is occupied and the earth activates the magnet and the selector steps onto the next outlet. (keeping that outlet private). If the bank contacts of the wipers were dirty, the selector would switch to an occupied outlet (the common misnomer of crossed lines). At Holborn Exchange I made out of the 50V bulbs a the words Merry Xmas, each letter lit up in a sequence using relays. The heat and current was quite significant, I also had some metal connected to some of the relays as a heat sync. Not sure if the H&S people would of allowed today.

[@ShellAndy]

"made out of the 50V bulbs a the words Merry Xmas, each letter lit up in a sequence using relays." There was one in Bristol Trunk ND too. I think there were a few scattered around the country, it kept the engineers sane.

[@cliff_young]

You could use a final selector on level 8 to connect to the recorded announcements. To swith to the next recording you could use the 6 second pulse from the pulse clock to drive the rotary relay on the final select, round the bank by one set of contacts to the next recording in sequence. Therefore vising each until the final selector drives out of the bank of contacts and resets. I think 6 seconds would be long enough to listen to each, and you could have the 8 recordings visited. 48 seconds in total. Room for 2 more on that level if required at a later date. Good talk chaps! Carry on the good work!! Thank you jonny for the production.

[@LOOKMUMNOCOMPUTER]

Cheers Cliff! Got me hands full right this second will read again asap so it digests! Cheers again Cliff!

[@LOOKMUMNOCOMPUTER]

Cheers Cliff! Got me hands full right this second will read again asap so it digests! Cheers again Cliff!

[@magicknight8412]

Something about old telephone exchanges fascinates me. So cool seeing this and learning how it all works.

[@lignesdefuite]

Hello from Canada, I love both channels and especially the electromechanical stuff. I look forward to hearing those clicks and whirs every week! For your light board, what if you run a separate power supply for the lamps on the load circuit side of the relays at whatever DC voltage/current is convenient? Then you could keep the control side period-authentic, but keep costs down and make your parts much less expensive. You might need to gut bulbs, soldering in your LED and then epoxy them back together, but they should last forever at a fraction of the cost of commercial B4 LEDs (if they're even available) Keep up the amazing work!

[@dcallan812]

"Hanging on the telephone" 🎵 Never really got into phone gear but its interesting to watch someone who is. 👍👍

[@Beardqt]

It's always amazing to watch a genuinely passionate person

[@TurboTimsWorld]

What we need is a diverter box to divert to the Red UK phone box at the connections museum! then we call and annoy Sarah at a UK call rate ! LOL

[@NTLife]

A private wire was something totally different, I used to work on Private wires back in the day

[@howiekeegan8804]

You're talking about private circuits? The P wire or Private wire in the Exchange ensures that the equipment used in the route through the exchange can only be used by one call. The P wire busies the circuit in use for that exclusive use of each call. Without it, you could , in theory, dial into a call already in progress. That's why it's called the private wire, to make each call private.

[@sparkyprojects]

The recorded messages could be for music of the week (from your synths), museum news, opening times etc. I always knew the P wire as the busy wire, meanng that the equipment was busy if a call was in progress Maybe have several relays to break the hold on the bank/grid If tose are not standard size bayonet, they go by diameter, B22 is 22mm, but they look like B15 golfball lamps, there are led versions

[@fractul22over7]

This is bloody awesome!!!

[@curtishoffmann6956]

Might be a good idea to start writing the numbers on the boxes so you don't have to guess what you're looking at...

[@davidlangdon6659]

I maintained UAX13 and other types of exchanges for over 25 years and am a volunteer at a local Museum in West Sussex where we have a working UAX13 that runs the museum's internal phone system and also we have other working Strower equipment. As you say the Pwire or private wire tells equipment if other equipment is busy or not but there is also the M or meter wire that connects the subsciber's meter to the final selector via the linefinder and group selectors. You have a lovely museum with many Strowger exchange artefacts we don't have room for. I must try to visit you sometime.

[@LOOKMUMNOCOMPUTER]

Nice to know David! If you ever visit please have a little look at the linefinders for us haha. At our whits end. We have a situation where the linefinders seize but also then the allotter proceeds to jump over to the next line finder and the call ends up seizing both. We will figure it out. But if you know of this issue and have any pointers. Please let us know! Even a few words might put us on the right track, thanks again. Sam

[@kasamialt]

You won't want the bulbs on the grid display to be too bright otherwise it could get quite blinding. You might be able to find bulbs designed for a higher voltage and under-run them a bit to manage both the current and brightness.

[@devttyUSB0]

What a cool rig you got there boiis. Thanks for sharing this talky-show-n-tell vid.

[@TDOBrandano]

You can probably run stock LED lightbulbs at 50 volts, depending on what LED driver they have on board. they generally have a bridge rectifier and a constant current driver chip that can take in a very large range of voltages, but some very primitive ones just have a capacitor dropper or have too many LED's in series to be drivable at low voltage. On the other end of the spectrum some 12v LED lightbulbs might run fine at 50v, again thanks to the constant current driver chopping the driving voltage down

[@LOOKMUMNOCOMPUTER]

Yep certainly doable. That is my last port of call. I am trying to find something that looks inkeeping. The last choice on the list is to modify the actual lamps with LED's

[@gcewing]

Robot voice says "THE NUMBER YOU ARE CALLING HAS BEEN EXTERMINATED!"

[@firenado4295]

the divert a call that has the eprom doesn't need a card in the front to work. I just plays the standard message with no card inserted, however I am not sure what happens with on as I also don't have one. I would assume a standard CF card would slot into that but I am not sure they had those back in the 80s.

[@LOOKMUMNOCOMPUTER]

Nice! Serves us right for not even trying it

[@firenado4295]

@@LOOKMUMNOCOMPUTER ah lol

[@RyanZerby]

I've lived in Michigan, Georgia and Nevada in the USA, and I've only ever heard them called "Alligator Clips". North America has Alligators, not Crocodiles... not sure if that is actually relevant.

[@colinstu]

What about American crocodile (Crocodylus acutus)?

[@Simple_But_Expensive]

Check McMaster Carr, Chicago Minature Lamps, or Jamesons for low voltage LED lamps.

[@LOOKMUMNOCOMPUTER]

Will do.

[@peterwilson8903]

The alliteration of crocodile clip is nice but the pleasing stress/unstress pattern of alligator clip shouldn't be overlooked.

[@UpLateGeek]

Sounds like This Exchange Is Not Obsolete Telephone Company PLC needs to hire more maintenance technicians!

[@steubens7]

can you float the ground (or v+), add 47 volts or whatever and use LEDs directly?

[@LOOKMUMNOCOMPUTER]

You can use led directly it is an aesthetic issue however hence not doing that quite yet as it would involve modding existing lamps. You could literally just use large current limiting resistors

[@DISCOTECHS]

There is a more advanced version of Divertacall that uses a ROM instead of a tape. The guy you met in Torquay, Devon. knows all about it and also knows how to program the ROM with audio. Avoid Black Face-Printed Divertcalls, as they need a P-Wire in all cases.

[@THISMUSEUMISNOTOBSOLETE]

nice! yeah we have one. its in the rack! its not working atm though. trying to find a full scematic of divert a calls. as only finding flow charts and simplified schematics atm

[@dedicatedspuddler7641]

Alligator clips over this side of the pond.

[@jeffreylewis4767]

Does anyone know if the person on the tape loop knows that they are “back online”?

[@madmodders]

Crocodile clips over here

[@electromechanicalstuff2602]

Watching nerds nerdgasm is the best. Lol.

[@traumgeist]

I’m no expert but it sounds like the clicky clacker in the malfunctioning uniselector needs a loobie doobie and then tap a it a few times with a wrenchie boi.

[@oldsoul-ms5gj]

I'm from Florida I called alligator clips

[@andysmith6289]

How much of this will work after the PSTN switch off December 2025, will it just be internal?

[@davidyates748]

It'll continue to work within the museum till the end of time, for external calls they'll need a VoIP to analogue telephone adapter, or ATA for short.

[@andysmith6289]

@@davidyates748 I wasn't sure if an ATA would work, assumed they are just very basic to work with an analogue phone. That's good news.,

[@KarlHamilton]

Just rip it out and replace it with a lovely System X install.

[@keithsquawk]

Proud moment when one central London exchange switched over. It started falling over reguarly and affected international companies universities and even some very important BT buldings. Apparently it had been configured for more domestic traffic than commercial and sulked as it got busy after lunchtime.

[@KarlHamilton]

​@@keithsquawk i think the first System X exchange had a duplicate number programmed in somewhere, and every time the guy picked up his phone to make a call the whole exchange shat itself. Would love to have been there to see that haha.

[@edgeeffect]

Ringing machine... ringing machine.... ringing machine.

[@ShellAndy]

400ms On, 200ms Off, 400ms On, 2 seconds Off 75v 25Hz ...... Oh god it's been almost 50 years, will I ever forget any of this?

[@edgeeffect]

@@ShellAndy Yeah, I've now got an "emulator" for that that runs on an ATTiny... it's a square wave not a sine wave but it sounds OK to me.

[@DISCOTECHS]

8w x 100 = 800 watts, (16 amps). how about 100 x SBC (size of your lampholders) Automotive LED lamps 12volts (cheap). Driven by transistors (Bistable flip-flops) easy to reset with 100 diodes..

[@THISMUSEUMISNOTOBSOLETE]

yep. i think we are going to go for automotive led lamps and just power them with a seperate 12v power going into the 100 relays

[@DISCOTECHS]

Just Occured to me.. Make sure you get BI-PIN type. As many cars take single pin. @@THISMUSEUMISNOTOBSOLETE

[@buidseach]

Why don't you set it up so people can dial in to listen to one of your tracks of music :)

[@LOOKMUMNOCOMPUTER]

It is setup! It well it was till the move. It'll be back soon :)

[@krirakayarthaya6846]

ದೂರವಾಣಿ ವಿನಿಮಯ ಕೇಂದ್ರ.

[@erdekind]

LCTs using ratchet relays....

[@LOOKMUMNOCOMPUTER]

Yes