Full Mechanical: The Panel Telephone Switch
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- Опубликовано: 6 авг 2024
- All about the sounds and workings of the telephone network. Let's start this off with the panel switch and how a basic intra-office call works. (That is, a call from a subscriber on a panel switch, to another subscriber on the same switch).
We'll show you how revertive pulse works, and what exactly is making all the noises you hear on the Phone Trips tapes. Make sure to leave a comment if you have any questions, and let me know if we should make more of these!
00:00 Intro & Explanation
2:35 Call through the Panel Switch
3:25 Battery & Dial Tone
6:20 Dialing
8:02 Decoder
9:40 How Selections Work
12:23 District Selections
17:20 Incoming Selections
20:32 Final Selections
23:10 Incoming Advance & Ringing
27:31 Review 
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As a teenager I was invited to poke around in a working panel office. I didn't try to understand what was happening , but I was fascinated by all of the action !
I grew up around this stuff. My Dad was a lineman for Michigan Bell from 1965-1996. All of this takes me back to the late 70s/early 80s. Truly fascinating.
I've been in step by step offices, crossbar offices, and an ESS office, but I never thought I'd ever see a panel office. Let alone still in operation! Thank you for saving the only one left in the world!! But ironically, the oldest switch of all, the Strowger switch used in the SxS system, was also the one that was in service
longer than all of them!
Some of them were even retrofitted for touch-tone, IIRC, but I could be confabulating that lol. But it's not beyond the realm of possibility, because obviously plenty of them were interfaced with digital offices.
It's probably safe(r) to say there are no panel offices anywhere in the world providing phone service.
But there are step offices that handle VERY few customers.
There may be a crossbar PBX still running somewhere in the world, perhaps even being used for residential phone service. Probably not tho, because mobile is now ubiquitous. I think that's what eventually did all the electromech stuff in.
Im not sure if we can say definitively that there aren't any in operation. I mean, I was blueboxing up until 1997 or so ...
✅
what an audio treat!
Makes me want to go back to my grandmother's home in Boro Park, Brooklyn, NY (718-436, or GEdney 6, as we knew it then) and listen again. I knew that her phone line was "different" but not exactly why. Calling into GE-6, from our Crossbar served line, we could hear the revertive pulsing coming back as the panel office soaked up the connection info. Grandma had a 300 set, which didn't have the same network as our 500 sets did, so the various clicks that came on call setup were much louder. It was fascinating then, and we didn't even have Sarah to explain it to us.
So many open contacts and so much mechanics. It's a miracle any call got through at all. The maintenance on these machines must have been overwhelming.
This is breathtaking. A lot of the techs I worked with had stories from the panel days, but I never worked with anything older than a 1A ESS myself. You've just filled in so many gaps in my understanding!
I'm loving all the content on this channel so far, and I can't wait until I can come visit the museum in person.
Glad you enjoyed it!
I worked on SXS, XY, DEX and DMS switches and had planned on visiting the last panel switch at Pacific Telephone in SFO but they ripped it right before I was able to go. At Bell System Private Line School, during the data section the mentioned that panel offices were notorious for impulse noise. I now understand why. Thank you! In the Army, our SXS and XY exchanges had end cells and end cell rectifiers. During high traffic, the end cells would cut in and add another 2V cell to the battery string. You could also tell when it was busy because the batteries would run down, so they wouldn't filter the 60 Hz hum from the rectifiers as well.
Evan Doorbell thanks you!
I rate this 2600 thumbs up!
This is so good, thank you! I really appreciate the detailed breakdown and high quality recording, and your narration is always a joy.
This is a masterwork in explaining complex concepts with just enough complexity included to make it accurate but not overwhelming. This video goes on my list of “when I grow up I want to make videos like this” :) Brilliantly done.
Thank you!
I would love to hear #1 Crossbar next. I just love hearing those Register Senders clicking away once you finish dialing. There's a certain charm that only #1 Crossbar has.
Totally agree. Love the #1 crossbar for this reason.
I savor my own childhood memories of dad's 1xb office. All them shafts n gears slowly revolving. I remember 5xb too. All that clickety clacking! But by comparison, a 1xb was a real kerchunkety kerchunker! And I saw it way back in the heyday! I even saw the battery room. The open-top battery cells. The copper power bus bars big around as "two-by-fours". The motors n generators big as 50 gallon drums! Just whirring away! The Great Satchmo summed it up quite nicely. "And I think to myself, what a wonderful world! Ohhh Yeeaaaahh!!!!!!!!!!!"
Nice work :) After listening to Evan Doorbell's tapes for ages this is helping to put the puzzle pieces together finally! More please!
+1 for adding the visuals to all of Evan's amazing recordings - superb :-)
@@disgruntledgoat Seconded! Well, thirded, I guess. 😁
Exactly my thought to. I mean Evan's tapes are nice to. But it's also nice to see a visual representation of the call going through. 😊
Nice to see people actually giving a crap about the technology Ma Bell invented. It's so fascinating how they pioneered this stuff, and how it was able to work automatically for nearly a century before digital circuitry came along and improved on it. I mean it makes sense HOW it all works, I'm still amazed by the WHY it's even able to work in the first place, y'know?
Technically, the switching is digital, just not in the solid state, computerized way we often mean
Longer than a century.
And look at it this way: there were electromechanical computers before solid-state (and even tube-based) ones. You think there's a lot of clicking coming from that crossbar? (Well, there is lol) Some of those electromechanical computers click even more. There is a huge one that they have somewhere in Japan that is open to the public. I think it might be the most advanced one ever made.
I still find it fascinating that it's able to work in the first place. I mean I get that it's an electromechanical computer, but man that's neat! Lol
@@zzco Well, I didn't mean to imply that you didn't understand the principle. ;-)
My grandmother’s line was on a step by step exchange, but my home phone in a different city was on a crossbar exchange. I used to notice when dialling home from my grandmother’s phone line I would hear the loud clicks of the equipment for the first 3 digits. After that, there were no background sounds for the final 4 digits being dialled, but as soon as I’d finish dialling the very last digits it would ring. There was never any delay. It was super fast with no audible clicks. When calling from my house to my grandmother’s house it was a very different sound because now I’m on a crossbar system calling into a step system. There were no noises at all on the crossbar when dialling until you reached the very last digit. You’d hear a double click. and a pause and then another double click that was a lower volume and then it would ring. If I called my friend who was on the same crossbar exchange I would hear the same double clicks , but then it would start ringing. No second set of clicks. I could be wrong but when calling my grandmother I always thought the crossbar system was sending the step system the last 4 digits and those had to be pulse dialled on the step side, which is why it would go quiet for 4 or 5 seconds before the second double clicks could be heard and the line would start ringing. I’ve always been intrigued with the sounds of the mechanical exchanges. I used them for so many decades that I was highly familiar with the audio routines they would go through, but this is the first time I ever saw what was going on to make those sounds. Thank you for showing us this Sarah. I loved this video. It was so educating. Thank you for the time you spent putting this excellent video together. It’s nice to know that the old mechanical stuff is still around. The phones make no sounds now with computers placing the calls these days and giving us artificial ring and busy tones generated by sound files. The old systems were more interesting and mysterious.
It sounds like your home was on a #5 crossbar. I lived in several places and moved from #1 crossbar, to ESS, to #5 crossbar. #1 was the most interesting sounding of the ones I lived with.
The last live Panel I heard was in 1980-81. While rare at that time, it was my favorite.
Davis P I drove my poor parents nuts hooking things up to the phone line when I was young. I discovered that you can listen in on the line without getting a dial tone if you unhooked one of the wires on the rotary dial. There were 2 white wires and one red and one green. If I unhooked the green one, I could pick up the receiver and hear into the line similar to what we were hearing in the video. Sometimes I could hear my neighbour talking in the far distance. Or I’d hear a busy tone or ring tone. It was very noisy. I decided to write a composition for school called, “How the Phone Works” and called Bell Canada asking them if I could have a tour for a school project. They were nice enough to let me go for a tour. NOISY. Inside it was like a million typewriters going. I asked the guy what the exchange system was called and he said C2. Would that mean crossbar 2? I don’t know but I do remember him saying that. This was 1975 by the way. I was there all afternoon. He even showed me how they could tell if the customer had more than one phone on the line by looking at the resistance on an analogue meter on a panel board that looks similar to the one Sarah sometimes shows. Back then phones were hard wired. No such thing as modular jacks in Canada until the 80s. They would fine people $500 for hooking an extra phone up to the line. The key is the bell. The bell is always connected even when on hook and it shows a lower resistance with each phone wired into the line. I was surprised he gave me all of these details. He was excellent. I wanted to work there but never did. Very hard to get into the phone company back then as they hired mostly family.
@@ds99 Actually an additional ringer generated a higher capacitor kick.. Because the ringer is in series with a capacitor. The capacitor was required to block the D.C. voltage. Enjoy.
The central office battery supply is calling for MAMA. Formants forming.
Or did it go sentient - DAM DAM DAM! No seriously, your deep understanding of every aspect of this system is amazing! Thanx for the explanation. It´s a treasure. I don´t know where else you could find this information in this quality! You´re awesome!
Amazing ! I didn’t understand everything , but I see and hear database queries and state machines and logic , feedback loops ... all done with mechanical elements !
Fascinating. Great work with this video.
When I was younger, I "experimented" a bit on Australian electromechanical gear and they must have used completely isolated talk and signalling paths here. While I remember we could hear a little of the signalling (especially on long distance calls to isolated places), it was nowhere near this much.
Many thanx for the video. I've always wondered how the Panel System worked. When I was a young tech here in New Zealand we had Western Electric Rotary Systems . 7A, 7A1 and 7A2. I can see how these two systems are related by the way of the Line finders, registers, sequence switches and group and final selectors.
"That's three clicks for incoming brush two: 0, 1, 2 Stop!"
Astrid, I absolutely love your dedication to this! You're just amazing!!! Thank-you, for people like you. Loved this video...even watched it a second and now a third time. Fascinating stuff. :) Love how you present this with so much passion and beauty.
I know this video is a while ago but I missed it first time round.
Truly brilliant in that I now comprehend the basics of the panel system and the novel concept of sequence switches which reflect state theory! The chart at the beginning of the video with the states listed was screen captured and printed; it made understanding later much simpler.
I finally twigged that the panel switches mapped onto Strowger vertical and rotary banks (pretty obvious really).
If only we had some panel switches in England …
Thanks ever so much.
Michael.
Amazing video. Brings a whole different level of detail to all those Evan Doorbell tapes. Thank you!
How these videos not have more views is beyond my comprehension.
The panel has to be my favorite switch, I think. They are mechanical marvels and I just love the sound of panel pulses. Thanks for explaining these as well as you do. 🙂
Such great detail and explanations of such a complex machine. I'm definitely looking forward to more!
I worked in a Panel office and can tell you it got quite noisy at times.
blimey, great excurse, thanks a lot. We never had such kind of exchanges, all we got were Strowgers and emd uniselectors (Siemens) until computers do their job. Thump up!!
WOW!!!😲 THAT'S SO INCREDIBLE! Even more incredible is that (I actually understood some of it. That "SENDER" "STEERING-RELAY" that runs through the contact of another relay... ("A" relay I think you said). THAT'S WHY YOU HEAR DIAL-TONE A FRACTION OF A SECOND AFTER THE DIAL STOPS! That's exactly what our phone line did in 1964 did! I was 5 years old, but I specifically remember that. Means we were connected to a "PANEL" switch.... I guess, ( If that's a characteristic of the "PANEL" ONLY? THANKS SARAH, YOU'RE INCREDIBLE!😅 JEFF
Awesome work, Sarah! I can’t wait for what comes next!
Sarah, You do such a beautiful job in these videos, I have very little electronics knowledge; however I really would love to learn about these old switches and you do such a great production. I am a former service rep for wireline Verizon. When I started working there the oldest of our switches online in the area code I worked would be a 3ESS.
Can't wait for the next part of this! This really brings some new understanding of the sounds heard in Evan's tapes!
This is an era of history I missed. Growing up in the Denver Metro, I was lucky to have been born after the 5ESS was installed in AURRCOMA. Never once have I heard ringing tones like this! Fascinating how such a huge machine sets up a straight through link between your phone to the other end! I would love to see a similar, but I imagine less in-depth because of so much of this being electronic circuits and not mechanical, detail of the sounds that 5ESS switches make.
Thank you for making this video! I just love the sounds along with seeing the mechanics work. Love to see a #1 Cross Bar next!
Good God, I am having flashbacks to the Evan Doorbell tapes. I love it! Can't wait to see more like this.
This is wonderful, Sarah - It's your best video so far!
Question: After reaching their selected groups, do not the district and incoming frame brushes travel up again in slow speed, to hunt for an idle trunk within the group? Perhaps for simplicity, you skipped over this detail to "selections beyond", but it would help in understanding the logic of Panel's "500 terminal" architecture. (or, perhaps your museum switch has but a single trunk in each group?)
You're right. I skipped over trunk hunting entirely, in an effort to simplify, and focus on just the important details!
Thank you so very much for this! You did an amazing job putting this video together. It had to take a massive amount of work to put together. Definitely worth it, I immediately had to share it with everyone I know. I was sitting here with my headphones and blushing in admiration like a little kid watching a fascinating science show. I am looking forward to the next episode. :D
Fantastic video, really enjoyed it. Keep em coming Sarah... THANKS
Very cool video. I've always loved the sound of the old telephone systems. It's really cool to see and hear them explained!
omg thank you so much for doing my request...... this is the best video to date here...... can't wait to see the crossbar
This is why I love panels and Step-By-Step switches. They provided lots of sounds for us to listen to. They're alive!
Excellent presentation! And love how you took special care of recovering the best possible audio via the interface..
Man this is kickass... grew up and started having an interest in the phone system in the 70’s.. thank you for doing this.
Amazing Sarah, it must have been a major task filming everything and then editing, making al the drawings, explaining all. Very insightful, higly appreciated! Thank you so much :-)
This is just what I needed today. Thanks!
Thank You so much, Sarah, for another truly fabulous video! The equipment you have in your museum, in each case, is likely the very last operational of it's kind! Switchman dad is still with me but his own memories are fading at this point. Panel was even before his time. He was 1xb n 5xb n TSPS. Nevertheless, Thank You so much for keeping this technology alive!
Listening to the machine like this is so intimate. It's akin to what Bob Moog said about having a spiritual connection to the inner workings of his creations. I know this might sound bizarre to people who don't understand, but it gives me goosebumps
I started my career in life safety telecom. 911 and alarm central stations. I worked on POTS lines and SONET rings, but I never learned anything from the CO side. This is fascinating. Thanks for making these videos!
Thanks for the great video and clear explanations. I have read generalities about this stuff, but it makes a lot more sense when I see you show the pieces in action. Keep up the good work.
OMG... I loved it, I got hooked up with the video from the beginning. I had the privilege to work for the Telephone Company of Chile back in the 80's & 90's in Crossbar Penta Conta Systems which for a long time was a mystery for me until I started learning the operation and intricated circuits, switches, relays, contacts, etc... so much stuff, incredible experience. I cannot wait to see your other videos. Also, my hands out to you on the level of knowledge of the system as complicated as it is. I also got to know the Siemens Step by Step System, another antique marvel. It blows my mind.
Oh my God this is an insanely informative and brilliant video!
This is really great. So much detail! I too would love to see a similar video about the crossbar system.
Very neat deep dive into what happens mechanically on these frames, and how it translates to the sounds you here. Some real neat history that would otherwise be lost
Thanks for adding actual captions for the Deaf
Wow even as an engineer it‘s hard to imagine this ever worked flawlessly… respect to the ingenious designers of this system which is probably unknown to most of the people who use it everyday and just taken as granted…
Thank you! This is so facinating. I once connected a speaker and small amp to my line before they installed my phone. It was a very cool experament. THANK YOU!!!!!
I always was curious to be inside Central Office, great job, thanks.
i love watching your videos because the coolest part (for me) is seeing how like all this cool ass, electromechanical stuff is like the bass for the way computer communication protocols and stuff were set up. Like it's just so cool. sad that this cool ass system with all these big huge electromechanical switches and complex little operations are now just like a computer though
Loved this! We didn’t have panel here in the UK so all of this was new to me, but you made it so easy to follow! Really love this style and am looking forward to more!
British Post Office nearly purchased panel switches for London. Then one of the British step by step manufacturers developed a 'director' using standard items which could convert the first three dialled digits to one to six routing digits (in-house call would use 1 digit and a tandem route 3 or more digits). It stored the last 4 digits on uniselectors which were sent on once the routing digits had been sent. BPO preferred to purchase British made equipment so it dropped negotiations with Western Electric and ran with step by step with directors for London and several other large UK cities.
Unbelievably complicated. Never imagined, thanks.
Absolutely amazing. Thanks for putting the effort into making this video.
That was amazing! A very professional video. It was technical enough to satisfy my curiosity about the details of panel. I already knew the basics but I never knew how the sequence switch worked. I would love to know more about the decoder and the sender and how exceptions like busy lines or trunks were handled. I remember reading that the first panels used a different design for the senders and I think they called it a translator instead of a decoder. Great work, Sarah. I can’t wait to see more videos and I want to visit the museum again when I can travel. -Will
Thanks for such an informative video Sarah!
It's certainly helped me put together things that have been floating around in my head from your previous videos and I understand the sequence of a call on the panel system at last. The only problem now is that I have oh so many questions about the panel sender! It would be great if you were able to do anything around that module but otherwise the crossbar process would be very nice to hear as a comparison. Thanks again for a great video :)
Very cool! I actually visited the museum one with a very similar recording setup, on the 5XB using the modular jacks by the OGT desk. I also noticed the hissing noise on the battery supply, and it seemed to change when the call simulator was started. I also think the capacitors in my 2500 set have changed value over time, because the tones are just noticeably different and OR wouldn't cooperate. Works fine on a modern line, though.
Brilliant presentation! 1972 I had a choice of 3 apprenticeship here in Australia. PMG (Post Master General) telecom, Police radio division or radio and Television I chose the later. Your brilliant presentation albeit using later technology that might have been used in the 1970’s gives me a great insight as to what I might had experienced if I had chosen the PMG apprenticeship.
Fantastic Video Sarah! I am only 150 Miles away but Tyler and I cant come and visit you and Astrid because the boarder is still closed. Thank you again for this video. I have so many panel switch questions. I could pick your brain all day...
Another great video, I have never seen a Panel office before these videos as we were first serviced by a Step By Step and now a 5ESS. I would love to see some #1XB next then maybe some more Panel.
Thank you for this wonderful video! My partner and I hope to be able to visit you once this plague is over!
Great videos. Thank you for making them.
I grew up at the point where mechanical equipment was being phased out in my area. Calling to rural office near me, the ring back sounded like this. Seeing it all works, and it all being explained, now I wish I could pick up the phone and listen for these sounds.
But I have a touch tone cordless on a VoIP line. :-(
Good video, good content. Thanks!
Amazing video! My suggestion would be for another switches “ideal call”, then once those are covered, come back and do corner and edge cases!
thank you
relays are cool i remember the sounds now that you mention it
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Absolutely brilliant! I used to hang out and make a pain in the neck out of myself at the local, independent central office when I was a 10-12 year kid (around 1970). On one visit, I was given a tour of the switch room. I've been looking for information on that switch for a very long time now. This is only thing I've seen that's close to what I remember being fascinated by that day. I may be misremembering, but I thought the switch I watched had some type of actuators moving horizontally as well as vertically. Either way, this is fantastic! Thank you so much for bringing this technology to life (keeping it alive and operating!) and explaining it so clearly! (I've been a phone nut my entire life... even got into the private payphone business the year it became legal.)
I remember when COCOTs started showing up, thinking how odd they were and trying to see if they could be gamed for free calls. ;)
@@poofygoof Coin return stuffing was the biggest annoyance. I had anti-stuffing devices, string cutters, etc. so stuffing wasn't profitable for the culprit, but it still sometimes disabled the payphone. Occasionally I had callers scam the operators, resulting in chargebacks to the line. The key to avoiding losses in these cases was to pay the extra for a legit payphone line - which was double the price of regular business lines. With a payphone specific line, chargebacks were always removed without question.
So very interesting , amazing that they figured this out , but still very confusing
very good introduction
I worked on 1/1A ESS switches between 1972-81 that had replaced panel offices. I remember when i worked on inter office trunks from my ess to a panel office instead of a wink back I would get what we called “a ride” from the panel . a series of spurts. The passing of the digits from our machine to the panel used “ revertive pulses “ instead of modern multi frequency tones.
Ha, that just happened to me yesterday when I was testing at a distributing frame. I love how you called it "a ride".
Great video. Thank you for taking the time to make it.
I have a few questions:
1. Are the trunks on the district selector multipled? That is, for each row of 30 (or even 60) TRS contacts, are they connected in parallel? Or are they connected in some other configuration?
2. Is each trunk on the district permanently wired to one specific rod on one specific incoming selector? I say "one specific" because I would assume in a fully equipped panel office there would be several incoming selectors. If I understand correctly there is only one in the museum.
3. What happens if you try to dial a 722 number that would have existed and been dialable in the original Parkway installation but which no longer exists in the museum configuration, presumably because the final selector that would have handled it no longer exists?
Has those numbers been busied out? (on the incoming selector I would assume)
4. Somewhat of a follow-up to the last question: if the incoming selector selected a trunk to a final selector which doesn't exist, what would happen? Would the sender time out because it was not getting RP back as expected and give you a reorder?
5. What happens if you try to dial a code that would normally have been routed over an interoffice trunk in the original Parkway installation? Do the decoders return the same information now as they did back then or have they been modified to handle non-722 codes differently?
6. Where exactly is the toneplant located, and how many leads are needed to connect it to the panel? Can you show where it's located, follow the cable(s) (if at all possible) and show where exactly it connects to the panel office? I know that's a bit of an odd request, but if you're looking for any video ideas, that is one detail I'm curious to see. :)
Thanks.
1. Each horizontal set of terminals (T,R,S) on the district frame runs all the way across, so that any vertical rod can access any trunk at any time. The rows are actually multipled between several district frames so that all trunks will be available to all rods on all frames.
2. Yes each trunk is wired to one incoming selector, permanently. And yes, in a fully equipped panel office there would be a great number of each, district, office, incoming, and final selectors. We only have one frame of each type.
3/4. If I dial a 722 number for which no final selector exists, the incoming selector will go up to the terminal where it would be, but it would find nothing there. The sender controlling the selector will "stick" and it will have to be "primed" (reset) manually. In normal operation, there would never be vacant terminals. They would instead be directed to a no-such-number announcement or an operator. This could be done here, but it would require wiring every single unused terminal to the machine, and would be somewhat laborious work. Instead, I multiple the series to other thousands blocks--so 5xxx and 4xxx go to the same exact place. Eventually, I will do it with some other thousands blocks as well.
5. In the panel office in particular, I have left the decoder as it was when the machine was taken out of service. (The 1XB, on the other hand, has had its marker wiring cut, so that none of the original routes remain.) There are several non-722 codes that can be dialed in the museum that will work. The ones that do not will just stick the sender, as mentioned above. In normal operation, vacant codes would have been routed to special vacant code trunks with announcements, but I do not wish to destroy the original decoder wiring in order to do that. I feel that it is historically significant.
6. Sure, I can show that. Our tone plant is very small, and not what would have been used in this office originally. We are possibly acquiring the correct tone plant for the panel, but as of now, we have nowhere to put it!
Connections Museum That would be so cool to be able to see the ringing machine that did “City Ring.” The current tones sound like one of the frequency multiplier electronic ones.
This is excellent. I worked SxS no.1 and SxS cama with intertoll class 4 and class 5 local for southwestern bell in the 70's. But this panel switch is really interesting to me. I used to read on options on cama senders for dial pulse, Mf, but revertive and PCI was foreign to me. How can I find out more. Working in the bell system was truly good times. I loved it. Thank you so much for showing this.
Panel switching has been as mysterious as it has been interesting. Now that I've learned this much, I want to know more. Can you stick with detailing the panel switch on the next video?
So awesome! Thanks!
Fantastic video! Can’t wait for more. Any chance for a sample pack or access to the raw files?
I have a bazillion takes, but they're all pretty much the same. Here are a couple that are interesting, including the actual final take used in the video. files.connections.museum/s/yJNXn6NL3KDDsdT
Awesome !!! Thanks so much! I live in Seattle and really need to visit post COVID.
You won't regret it, I promise.
I love this series! I want to know all of it, lol. Keep going, but also go back to #1. Also, how does that ringing circuit work? Is it just pulses of a given voltage across a certain time period? Thanks so much for this, it's absolutely fascinating.
Excellent!!!!!!!!!
Awesome! Thanks!
Thanks for the video I always wondered how it worked in the USA. I'm from the UK we have Strowger.
Thanks Sarah for a great video. I would love to know how a call Trace and the operator interrupt worked in those days.
Freakin AMAZING!
just saw a video from the pethericks--ready for pipes-reminded me of the panel switch-lots of rods-lol
Thanks Sarah
Wow, HAvermeyer 4, 6, 9, NEtown 9, still have my PICS.
So many questions, so little space:
1) Coupled to the CO battery on-hook as you did (and heard audible noise), could you capacitively couple and talk to someone? What about post dial tone or during busy?
2) What if you dialed 2 or 6 digits and stopped, would the equipment be tied up (i.e. sender & decoder)? If not, which part monitors for this condition?
3) What if no line finders are available when going off-hook, what do you hear (i.e. during emergencies)? Expect silence but maybe the line relay covers for this?
4) What prevents you from dialing faster than the panel can search for the next available panel? Example: 722-1111
5) Does this office support billing info, or does it pass toll calls to an office (or operator)?
6) Was there ever DTMF capability?
Was planning a trip across country for a tour, then COVID-19...
Thanks!
1) I've never tried talking over unfiltered CO battery, but you could probably talk over it, yes! The only problem you'd have is that you'd have to overcome all of the inductance from all of the relay coils that are sitting on that raw battery. Basically, some of your voice current would disappear into relay windings and get turned into tiny magnetic energy, so it wouldn't end up traveling that far. (The relay coils that normally sit in a talk path are designed to be transparent to the AC current of your voice also, but they direct that current in a particular direction--to the person you have called). On the other hand, talking over busy tone is something that *can* happen on some switches. Evan Doorbell has plenty of recordings of that!
2) If you dialed and then stopped the sender would be sitting there waiting for you. There is a timeout condition (about 30 seconds) where you would be transferred to a holding trunk and the sender would let go and go handle someone else. It's called "permanent signal" in the telephone world.
3) If no line finders (or senders) are available, you would hear nothing. (You would likely run out of senders before you ran out of line finders) That's exactly what dial tone means--that there is equipment available and ready for you to begin dialing. In the panel switchroom, there would be quite a racket though, as the equipment would be frantically searching for a sender and not finding one.
4) Nothing prevents you from dialing faster than the panel switch can search. That's actually expected. The sender merely stores/buffers your digits, and completes the call as it is able to. I dialed slowly in this video in order to make the steps more understandable.
5) This office supports local billing (message registers) for calls dialed within the city. Long distance would have gone through an operator or (eventually, by the 1960s) through a separate long distance tandem switch for billing and completion.
6) There was DTMF capability in some panel offices in the 1970s, but never in Seattle. In some cities, support was added via 3rd party devices like this: telephonecollectors.info/index.php/browse/bc-switching-library/teltone/3787-teltone-m-164-convert-a-pak-models-70-71-72-and-73
Wow! You have a 5ESS. Know that like the back of my hand. If you ever have questions, feel free to reach out.
Excellent!!! Stay safe time machine :-)
I’ve been watching forever but this is my first comment. I am distressed that never once have you spoofed us with, “Hi I’m calling about your car’s warranty.”
Having been inside several types of operating offices (5XB, SxS, 1ESS, 2ESS), it is nice to see how a panel office works. My question: Can you dial "too fast" for the switch to react. The tours were arranged because we had DID trunks for the equipment we worked on. If you didn't have battery going back to the CO, you could drop trunk availability, or (5XB) stick senders, which they really didn't like. The SxS stuff was a bit easier to "see" the call. In the early 70's they had a SxS PBX where I worked. Fun to get the keys and look inside, or just visit with anyone who was working on the switch itself. You don't see much of things nowadays with the DMS100 or 5ESS.
Wow, that was brilliant, thanks so much. That was really detailed and interesting, even if you did leave a load out for pacing reasons.
Even filtered like that, the *thunks* of the dialling pulses were a bit much with headphones, but maybe I need to go listen to some more loud music :D
Questions I have:
* How does this system differ from the equivalent UK system, if at all (though I doubt you know much about that - I'm a UK geek and I've a mild interest in telephony, is all).
* How does the selector memory system work? I could see a knot of wires and some closed cabinets - is it a relay-addressed wire-wrapped plugboard, or is there more to it?
* In the sender, is there a bank of ?10? relays per dialled digit, or do banks get reused once the digits have been dispatched to the relevant frame? I guess that would only be possible if frame setup occurs during the dialling process rather than once the user has entered all the digits.
• Panel system were never installed outside of North America. The UK used Step by Step (aka Strowger) equipment, and eventually Crossbar. Those both work very differently than panel.
• Perhaps Sarah can explain the decoder (memory) system in another video sometime
• The sender uses just 5 relays to store each digit, using a two-out-of-five code
• The selector switch drive seems to be pretty reliable.
--Like has already been mentioned. The UK used mostly step, and then eventually a form of crossbar. The panel switch is quite different. (For a while, the panel's sister switch, known as the "7A Rotary" was installed in various parts of Europe. Developed initially by Western Electric in the US, and then moved to their plant in Brussels.
--The sender portion is definitely worth its own video. It's quite complex.
--There are recording relays for each of the 7 digits plus an extra set for the "stations" digits (for use with party lines). Each digit is recorded by some combination of 0,1,2,4,5 relays.
The sequence switch 90 degree drive is quite finicky. It is indeed metal-on-metal contact. The friction is provided by a pumice stone and a cup of water. Every so often you have to go around and grind them with the wet pumice stone which will cause a layer of rust to form on the discs. The rust is required for the switches to operate! If a museum visitor touches the discs and gets oils from their fingers on them, I have to clean them with alcohol and then re-rust them.
@@ConnectionsMuseum In today's terms I suppose the rust would be referred to as a "thin coat of oxide"?
@@ConnectionsMuseum Great, thanks.
- I sense a rabbit-hole forming, and now I have some search terms... :D
- I'd be interested in further videos, both on the sender system and the decoder memory. I seem to recall a previous sender-debugging video of yours, will have a look for it.
- Interesting, a variant binary code. I thought I saw 10 number relays in the A register in the video of the sender yesterday, but on careful re-examination today I see that what I took as a continuation of the A register (on the right of screen) was actually a bank of different relays (PS and a set of FOx relays), one of which (FO3) tripped when the A register finished loading (I think).
- How strange. In most cases I know of (mainly re-enactment swords, to be fair), getting skin oil on the metal /causes/ rust ... but of course metals and their uses and needs are different. Ah, visitors and their touching things...
@@makingconnections Thanks for the reply. As I said to ConnectionsMuseum just now, I sense a rabbithole forming, but now I have some search terms. I agree that the selector drive seems pretty reliable - I remember several videos about the selectors where it seemed like everything /but/ the drive was faulty - but based on this description I'm surprised about that :)
More panel!!! Screw that modern crossbar stuff...
No, the old crossbar was interesting also! It's the modern ESS that's boring, it just sits there all you hear is a fan running.
Question: how did the sender & decoder handle the district frame for long distance? I worked in a CATV digital headend in the mid 2000's. I was part of the digital video + VOD team, but our brother admins in the master NOC were in the VOIP team, and we shared knowledge about the different systems in convo all the time (read: Unix/Linux nerds drinking heavy at the end of the week, sharing war stories). Watching circuit switching here vs. packet switching telephony is a very interesting contrast. So many similarities and yet so differently executed!
Good question. The decoder doesn't handle long distance at all. The panel switch was designed before automated long distance switching was possible, so it only handles local calls. Before the 1950s, long distance calls were handled by operators. After the 1950s, the senders themselves were modified to recognize area codes (X0X or X1X), and send those calls to a separate long distance switch for processing.
Very cool. Ill bring my Blue Box with me when I visit and find a payphone somewhere in the building, and make long distance calls for free, thus beating the man
Good description. I am building a tiny PBX to route calls to other local rotary dial telephones ( not connected to outside lines). I notice the dial pulses I get on the oscilloscope are nice and clean, but at a real central office, I don't see how the equipment could determine the pulses from the noise.
Insane!
Interesting. I know Providence, RI had a panel switch until about the mid 70's.