I had the privilege to work for the Telephone Company of Chile in the 80's & 90's and I was part for a couple of years of the OGT team. That was a beautiful experience. We had on those days groups of technicians working in the field, attending customers calls with damaged phones and lines as well as other services. It was the most crazy, insane and rewarding job I've ever had.
Thank you for keeping this technology alive and sharing it with the world! I love how you went a little more into the details of the keys and switches of the OGT, you did an awesome job of explaining and demonstrating it. Thanks :D
I wanted to write a big thank you somewhere and this seemed as good a place as any!!! I love these videos. I LOVE the enthusiasm!! And I LOVE that you don't edit out every error because I often learn from the wrong turns left in the videos. I appreciate that. In the early/mid 1990s I had a friend who at the time was a central office tech. He showed me inside a couple central offices and I was fascinated. I believe my own office at that time was 1AESS but it was a long time ago. I later got to see it again just before it cut over to a 5ESS. My friend used to call high volumes "Bitch'n Switch'n". He also liked to joke that the dial tone was supplied by a dial tone tank and that if you ever didn't have dial tone, they probably just didn't get the tank refilled in time. Keep up the good work on this stuff. I'm thinking of coming out to visit when covid19 slows down. THANK YOU AGAIN!!!
So, I got off work at one of the remaining wireline phone companies, and what do I do? Watch a video about a phone test desk. I love all of these videos so much.
Great video. Back in the 70s in Canada you were not allowed to plug in your own phone. The phone company controlled how many phones were on your line and you paid monthly rent for each phone. I imagine it worked the same in the US. People who were caught hard wiring extension phones could be fined. There were no modular jacks. Everything was hard wired. When I went on a tour of our local phone exchange the people sitting at a desk similar to the one in your video, would spend time checking the resistance of people’s lines to see if they had more than one phone connected when there should only be one phone. If the resistance was lower than expected, they would know that there’s possibly an extension hooked up. The bell was always connected even when the phone was on hook. This is why the resistance would be different. Some people who wanted a free extension phone would disconnect the bell of the second phone to bring the resistance back to normal. That meter you had in the video looks like the one they were using in the office to verify the number of phones connected. I saw this in the mid 1970s but my interest in this technology was very high so I remember it. I find this very interesting. Thanks for the video.
That's strange. I live in Canada and that wasn't the case where I lived in Peterborough Ontario. In 1975 we had modular jacks and put a second phone in the basement and no one cared if we had an extension phone.
In the US, up through the 60’s we had 4 pin plugs that allowed us to connect to any phone Jack in the house. Phones were rented from the telco and you paid according to the number of phones you rented. Used phones were available through a kind of black market. Mostly Stromberg Carlson phones, and occasionally a western electric phone might be for sale. My Dad bought several phones and I disconnected the ringer so that the telco couldn’t detect the increased ringing current. Never got caught.
@@billmoran3812 I had an aunt who had one of those 4 prong square plugs. I forgot about those. She paid a monthly rental fee here in Canada for that luxury which is why it was rare to see it. In 1976 I got into big trouble because I had the phone line plugged into an amplifier. Apparently a surge of electricity went through the line and blew a fuse at the exchange that night so the repair guy was on our doorstep in the morning the next day. I was at school and he asked my mother if anything was connected to the phone line. She said no and she wouldn’t know. At 12 I knew not to tell her what I did. He asked if he could inspect the line in our house and mom let him in. He found speaker wire hooked into the terminal box in the basement and used some device to trace the line under the carpets and up 2 storeys into my bedroom. Got the wooden spoon pretty good when I came home from school for lunch. He told mom that they could be fined $500 and even jail time for touching the phone network. He gave mom a rotary desk phone (Northern Electric) and told her to give it to me to experiment with so I would stay off of the real phone line. I thought he must have been the nicest man. Mom wouldn’t let me have the phone. She was afraid I’d hook it up to the line.
Great video. I worked No5 cross bar for years and spent a many many howers testing trunks from the OGT. The one thing we always did was make the trunk busy before testing so we don't stick senders.
Thanks for posting, Sarah! I love the Panel Switching System and seeing how it all worked is fascinating. It's really a testament to the ingenuity of the designers. Looking forward to the next one!
Sara, I want to know how you learned so much about early telephony. Your videos are legendary. One thousand years from now, historians will think you actually used this equipment when it was in production!
In the early 70s I was an admittedly poorly motivated panel switchman, but I was great working the OGT. 80% of the time I was on hold, waiting for other poorly motivated frame personnel to give me a short or open on a trunk in some distant wiring frame. Normal people hated it, but I loved being in my own head, as far from the phone company as I could get.
Thanks so much for making these videos. My mom used to work for one of the Bells in Vermont before dial was implemented. I have heard so many stories as a child of those days, and I even have office phone books for the town in which we both grew up. It's very cool to see equipment that quite literally took her job away so she could become my mom :)
I think it’s fun to imagine all the people that have sat in that exact position using that exact equipment, and the fact that was someone’s “real job” and all the training they must have gone through. It’s kind of amazing this equipment still exists and it’s available for us to explore and go back. Very cool.
Dayam! I feel like I signed up for an hour education tour at a museum but I arrived 45mins late. I didn't learn anything! Without a basic intro to offices and trunks and where things are located in reality vs simulated.
Much less involved, but I worked in AM radio in the early 80s. The basic look of this equipment reminds me of the old RCA boards. Toggle / throw switches, especially. And as solid as a WWII tank.
You look amazingly cute and I love that you're describing this equipment for us on UA-cam -- infinitely better than listening to vintage audio tapes. Can you do a really really in depth Crossbar 5 video?
There's lots of stuff I couldn't understand due to my ignorance..... but still.... the video was very interesting. Keep it up. May be you could make some videos about the basics of how a phone worked and gradually increasing the difficulty and talk about how all those commutators work. From A to Z. You could make a series out of it :) Anyway... I subscribed ...
I retired from the telephone company 22 years ago. I worked in carrier and we also tested trunks in xbar 1. I worked on d1 and d3 and d4 channel banks. T1 .t2,t3’s. E1 and e2’s and e2-3’s( these were tube repeaters) e6’s. Mft’s. 206 repeaters,232 and 236’s and associated dsx1’s.How about n carrier, I only worked on repeater bays, they were fun. Musack circuits, alarm circuits. Dll’s, wow so much fun. Fault locate t1’s to manholes. Subscriber line carrier. Slc7. I remember.
Thank you for showing how the permanent signal works. May you do a video the howler showingwhat switch it is and how it sounds, please? Thank you. I have been watching Evan Doorbell but couldn't find that certain off hook tone that was a constant medium pitch single tone.
The panel office I worked in disused the tie line and misc keys add installed a call director instead. I would have preferred the original setup because you could monitor a trunk you were working on while talking to a frame tech.
Thanks so much for posting this video! I've loved everything you've posted so far, but this one really illuminates this photo in a way I never could have imagined: en.wikipedia.org/wiki/File:Panel_Office_Typical_OGT-colourbalance-2.jpg
I notice there never seems to be any talk of a clock pulse. What happens if two relays try to grab the same trunk at the same time? And similar clashes. Also it seems some lines have fuses and others have current-limiting incandescent lamps. IS there some general rule as to which lines get fuses and which get current-limiters?
There are no clock pulses in these machines. Everything just runs at its maximum speed, limited only by their physical properties (magnetism, moving mass, motor speed). When a selector lands on a set of terminals, it grounds it almost immediately, marking it as "busy" to other hunting selectors. There is an inherent 5-10 millisecond window called the "unguarded interval" where a selector will be on a terminal but it will not be grounded. During this window, another selector could land on the same terminal and attempt to seize it. This was not really a well-understood problem during the 1910s when they were designing this machine, and it proved to not really be an issue for most of its life. However in the 1960s and 1970s as the parts began to age, and fall out of adjustment, the 5-10 ms window became 3 separate intervals, some as long as 50-100 ms. This was a big problem, and required a set of adjustments to be made on the affected selectors. They came up with a test device that could be attached to each selector and identify the ones most seriously affected. Until the issues were corrected, there were many double-connections. In later common-control machines like the No. 1 and No.5 Crossbars, contention was not only anticipated...it was expected. These machines were designed from the outset with the idea that many pieces of equipment would all be trying to access things at the same time. When a marker (analogous to a CPU) seized a frame, it had to bid for that frame against other markers. When it was awarded access to a switching frame, it had complete control over that frame until it was done. A single operation usually took less than a second, so many markers could access many frames, as long as everything was protected by timers...which it was. The resistance lamps are used in circuits where there is a large variation in the amount of current that could pass through, but as the current becomes higher, we want to limit it gracefully, until we reach a theoretical maximum and then just hard-limit it. A good example of this is line circuits, which extend out of the building to subscribers' telephones. We provide battery to those phones, and depending on the external loop resistance of their line, there might be a very high, or very low current flow. If the subscriber is close, there will be high current, which we will have to limit. If they are far, there will be lower current, which we do not have to limit quite as much. If their line is shorted out just a few meters from here, there will be *very* high current and we need to hard-limit that.
Hey Sarah, I was wondering, can you explain how the Panel switch actually manages to stop at the correct trunk when it is revertive pulsing? I have always imagined that by the time it sent the revertive pulse, and the far end office told it to stop moving, that it would have already gone past the trunk. Does it have a sort of offset track that causes it to send the RP before it actually makes contact with the trunk?
Good question. I should maybe do a video about this, but I'll try to briefly explain here. Panel offices actually had a physical distance limit between them, partially due to this very problem. The way they got around that was to send the pulses back to the sender *slightly* earlier than the actual moment when the brush was contacting the proper terminal. This allowed for the round-trip time, plus the operate time for the relevant relays. Then, when the power was cut to stop the up-drive, there was a special commutator known as the "C" commutator that kept the circuit closed through itself *just long enough* to make sure that a ratchet at the bottom of the clutch assembly fully locked into its pawl to hold the selector in position. If the alignment of the brushes and commutators was incorrect, it resulted in a wrong connection, so it was very important that they were kept within specified limits. See this page from a switchman's notebook we have: revertive-pulse.tumblr.com/post/151866538129/the-owner-of-this-notebook-is-very-good-at-writing
Sarah great video. Now I am curious as to how "permanent signal" works in the world of digital 'switches". I know what happens in southern California when a phone is off hook, we get the fast loud busy signal through a receiver. If there is a shorted circuit, does the computer generate a ticket for the possible need of repair, or is there still a real person which intercepts and double checks. Imagine if Cell phones could be "taken of the hook" haha
DandyDon Sarah here. It's almost certain that a computer generates a report that gets looked at by a manager somewhere. With newer switches like the 5ESS, capacity isn't as much of a problem. With the decline of wireline service, most of them are running way under what they can actually support.
Does the load shedding function have any way to respect emergency calls from low priority subscribers? I'm not sure how it could since you'd need the very senders your trying to shed load on to dial the emergency services. Does this pre-date 911?
Nope! After an earthquake or whatever, you change who is allowed to use the phone every 20 minutes. First group A, then B, then C. Then back to A, and so on, until the volume dies down enough that you can have more than one group on at a time. The thinking was that if you had a hard capacity limit, there was no way to tell which calls were genuine emergencies, and which calls were just people calling their friends. This *does* pre-date 911. The police had a phone number, but it was a regular telephone number just like everyone else. In 1923 they didn't have it all figured out yet :)
@@ConnectionsMuseum Normally Class A (Police, fire, doctors, hospitals, etc) would always have service. Classes B and C would be alternated unless load was very high in which they would both be suspended. Remember also, Line load only affects origination of calls. So if you were on class C and were cut off, your could still receive calls from any other class, but not receive a dial tone.
In movies when there would be a disaster and they'd pick up the phone and get no dial tone, I always just assumed their line was cut. But they could have also been out of senders or line finders. I never thought it would be a capacity problem because I thought dial tone was just connected to everyone's phone all the time when they weren't making a call.
Do the trunks use DX signaling? Two or 4 wire? Or revertive pulse? Maybe DX signaling wasn’t invented when first panel office came on line. Are any subscriber lines ground start capable?
Trunks are 2-wire loop start. No 4-wire, as panel was not capable of toll operation. That would have been handled by operators. I don't know that any lines were ground start. I see no evidence for that in the schematics, but I haven't looked at all of them. Regular subscriber lines were definitely loop start.
@@ConnectionsMuseum when I was in NYC in 1974, local office 212-WAlker 5 nnnx was panel and we had direct distance dialing. Inter LATA calls must have been handled by #4 office post WWII. Our Sprint (formerly SP Communications) trunks to NY Telephone were mostly 2 or 4 wire DX / e&m. BTW does any of your machines have a 1004 test line and 600 ohm termination? None of these test lines work anymore in the real PSTN
@@sethtaylor5938 Yes, we have 1004 Hz at 232-0003, 832-0003 for the 5XB and 1XB. There's also a sup test line. I have not wired up the silent termination lines yet. The panel has a flashing busy test line at 722-0099.
@@ConnectionsMuseum BTW where I retired from in NJ 973-540-9971 will get 1004 @ -10 dBm and 540-9966 is 5 seconds of 1004 then 600 ohm quiet term. Also in old legacy VZ ex NJ Bell if u dial 958 (ANAC) on subscribers line in area codes 201, 973, 732 and 908 the switch echoes back the seven digit phone number in a voice message. Kinda unique to old Bell System. Some offices also used 959 especially in Canada. We used that as a trouble shooting tool sometimes at the Main Frame. Telco outside plant used it a lot.
I kinda envy you because you are working on the equipment I first used growing up, and you're around my age. I love this kind of physical electromechanical technology, because the circuits made are actually moving. Unfortunately, I love the internet and the newer technology much more. And as we both know, there was too much noise on the lines I. The HF range to allow this technology to work with each other properly. I was about 6 when they phased out the old crossbar and panel systems in Orlando Florida. My favorite switch was the crossbar 5. I still don't fully understand panel. But I bet I'd love it if I fully understood it. It's like a simplified reverse of the crossbar technology I think (in terms of logic)(maybe parallel to the logic of crossbar).
Imagine if we made computers with similar moving Technologies. Meaning imagine if we made Dion off computer functions happened Electro mechanically. It would be a huge circuit but it would work much the same but very much very much slower.
![[Panel] How does the line finder work?](http://i.ytimg.com/vi/0Qvsh6BC2lQ/mqdefault.jpg)
![[Panel] How does the line finder work?](/img/tr.png)
I had the privilege to work for the Telephone Company of Chile in the 80's & 90's and I was part for a couple of years of the OGT team. That was a beautiful experience. We had on those days groups of technicians working in the field, attending customers calls with damaged phones and lines as well as other services. It was the most crazy, insane and rewarding job I've ever had.
Thank you for keeping this technology alive and sharing it with the world! I love how you went a little more into the details of the keys and switches of the OGT, you did an awesome job of explaining and demonstrating it. Thanks :D
I wanted to write a big thank you somewhere and this seemed as good a place as any!!! I love these videos. I LOVE the enthusiasm!! And I LOVE that you don't edit out every error because I often learn from the wrong turns left in the videos. I appreciate that.
In the early/mid 1990s I had a friend who at the time was a central office tech. He showed me inside a couple central offices and I was fascinated. I believe my own office at that time was 1AESS but it was a long time ago. I later got to see it again just before it cut over to a 5ESS.
My friend used to call high volumes "Bitch'n Switch'n". He also liked to joke that the dial tone was supplied by a dial tone tank and that if you ever didn't have dial tone, they probably just didn't get the tank refilled in time.
Keep up the good work on this stuff. I'm thinking of coming out to visit when covid19 slows down. THANK YOU AGAIN!!!
So, I got off work at one of the remaining wireline phone companies, and what do I do? Watch a video about a phone test desk. I love all of these videos so much.
Great video. Back in the 70s in Canada you were not allowed to plug in your own phone. The phone company controlled how many phones were on your line and you paid monthly rent for each phone. I imagine it worked the same in the US. People who were caught hard wiring extension phones could be fined. There were no modular jacks. Everything was hard wired. When I went on a tour of our local phone exchange the people sitting at a desk similar to the one in your video, would spend time checking the resistance of people’s lines to see if they had more than one phone connected when there should only be one phone. If the resistance was lower than expected, they would know that there’s possibly an extension hooked up. The bell was always connected even when the phone was on hook. This is why the resistance would be different. Some people who wanted a free extension phone would disconnect the bell of the second phone to bring the resistance back to normal. That meter you had in the video looks like the one they were using in the office to verify the number of phones connected. I saw this in the mid 1970s but my interest in this technology was very high so I remember it. I find this very interesting. Thanks for the video.
That's strange. I live in Canada and that wasn't the case where I lived in Peterborough Ontario. In 1975 we had modular jacks and put a second phone in the basement and no one cared if we had an extension phone.
In the US, up through the 60’s we had 4 pin plugs that allowed us to connect to any phone Jack in the house. Phones were rented from the telco and you paid according to the number of phones you rented.
Used phones were available through a kind of black market. Mostly Stromberg Carlson phones, and occasionally a western electric phone might be for sale. My Dad bought several phones and I disconnected the ringer so that the telco couldn’t detect the increased ringing current. Never got caught.
@@billmoran3812 I had an aunt who had one of those 4 prong square plugs. I forgot about those. She paid a monthly rental fee here in Canada for that luxury which is why it was rare to see it. In 1976 I got into big trouble because I had the phone line plugged into an amplifier. Apparently a surge of electricity went through the line and blew a fuse at the exchange that night so the repair guy was on our doorstep in the morning the next day. I was at school and he asked my mother if anything was connected to the phone line. She said no and she wouldn’t know. At 12 I knew not to tell her what I did. He asked if he could inspect the line in our house and mom let him in. He found speaker wire hooked into the terminal box in the basement and used some device to trace the line under the carpets and up 2 storeys into my bedroom. Got the wooden spoon pretty good when I came home from school for lunch. He told mom that they could be fined $500 and even jail time for touching the phone network. He gave mom a rotary desk phone (Northern Electric) and told her to give it to me to experiment with so I would stay off of the real phone line. I thought he must have been the nicest man. Mom wouldn’t let me have the phone. She was afraid I’d hook it up to the line.
Great video. I worked No5 cross bar for years and spent a many many howers testing trunks from the OGT. The one thing we always did was make the trunk busy before testing so we don't stick senders.
Thanks for posting, Sarah! I love the Panel Switching System and seeing how it all worked is fascinating. It's really a testament to the ingenuity of the designers.
Looking forward to the next one!
Sara, I want to know how you learned so much about early telephony. Your videos are legendary. One thousand years from now, historians will think you actually used this equipment when it was in production!
In the early 70s I was an admittedly poorly motivated panel switchman, but I was great working the OGT. 80% of the time I was on hold, waiting for other poorly motivated frame personnel to give me a short or open on a trunk in some distant wiring frame. Normal people hated it, but I loved being in my own head, as far from the phone company as I could get.
Fantastic video! It really blows my mind that machines like this existed in 1923.
Thanks so much for making these videos. My mom used to work for one of the Bells in Vermont before dial was implemented. I have heard so many stories as a child of those days, and I even have office phone books for the town in which we both grew up. It's very cool to see equipment that quite literally took her job away so she could become my mom :)
I think it’s fun to imagine all the people that have sat in that exact position using that exact equipment, and the fact that was someone’s “real job” and all the training they must have gone through. It’s kind of amazing this equipment still exists and it’s available for us to explore and go back. Very cool.
Fabulous video. I knew nothing about cross bar exchanges, but now I do.
Sarah, I love your enthusiasm. Thanks for making these videos.
Dayam! I feel like I signed up for an hour education tour at a museum but I arrived 45mins late. I didn't learn anything! Without a basic intro to offices and trunks and where things are located in reality vs simulated.
Much less involved, but I worked in AM radio in the early 80s. The basic look of this equipment reminds me of the old RCA boards. Toggle / throw switches, especially. And as solid as a WWII tank.
Great video! Thank you for making these videos, phone switching is fascinating! :)
Excellent presentation
Thank you so much for the video and do please keep them coming!
Watching you flick those switches reminds me of testing on the old 3C test desk before MLT came out. Long long ago.
You look amazingly cute and I love that you're describing this equipment for us on UA-cam -- infinitely better than listening to vintage audio tapes. Can you do a really really in depth Crossbar 5 video?
There's lots of stuff I couldn't understand due to my ignorance..... but still.... the video was very interesting.
Keep it up.
May be you could make some videos about the basics of how a phone worked and gradually increasing the difficulty and talk about how all those commutators work. From A to Z.
You could make a series out of it :)
Anyway... I subscribed ...
Another very interesting and cool video, thanks for your always educative, informative and entertaining video! :-)
Awesome! Keep it up!
I retired from the telephone company 22 years ago. I worked in carrier and we also tested trunks in xbar 1. I worked on d1 and d3 and d4 channel banks. T1 .t2,t3’s. E1 and e2’s and e2-3’s( these were tube repeaters) e6’s. Mft’s. 206 repeaters,232 and 236’s and associated dsx1’s.How about n carrier, I only worked on repeater bays, they were fun. Musack circuits, alarm circuits. Dll’s, wow so much fun. Fault locate t1’s to manholes. Subscriber line carrier. Slc7. I remember.
Awesome demo. Very interesting.
Your badge says 'Panel Witch" lol
Love your videos
Thank you for showing how the permanent signal works. May you do a video the howler showingwhat switch it is and how it sounds, please? Thank you. I have been watching Evan Doorbell but couldn't find that certain off hook tone that was a constant medium pitch single tone.
Lapel microphones! You can still record good audio in bad audio environments.
IKR you'd think them being in a communication museum they's know this stuff..
@@Elfnetdesigns Telecommunications is very different compared to professional audo-video recording or producing...
Thanks for the great explanation, Sarah! I'm looking forward to more videos like this.
Indeed! That was very interesting, keep them coming! :)
Thanks! I'll do more videos like this in the future.
The panel office I worked in disused the tie line and misc keys add installed a call director instead. I would have preferred the original setup because you could monitor a trunk you were working on while talking to a frame tech.
As good a video as ever - thank you.
Love the videos! im subscribed I can't wait for more.
Thanks so much for posting this video! I've loved everything you've posted so far, but this one really illuminates this photo in a way I never could have imagined: en.wikipedia.org/wiki/File:Panel_Office_Typical_OGT-colourbalance-2.jpg
That's a cool photo! I'd seen it before, but not this hi res version.
I spent many hours at one of these testing trunks and shooting trunk troubles...
Wait...Sarah? There's a Sarah AND an Astrid? Are they identical twins or am I goig nuts??!!
I notice there never seems to be any talk of a clock pulse. What happens if two relays try to grab the same trunk at the same time? And similar clashes.
Also it seems some lines have fuses and others have current-limiting incandescent lamps. IS there some general rule as to which lines get fuses and which get current-limiters?
There are no clock pulses in these machines. Everything just runs at its maximum speed, limited only by their physical properties (magnetism, moving mass, motor speed). When a selector lands on a set of terminals, it grounds it almost immediately, marking it as "busy" to other hunting selectors. There is an inherent 5-10 millisecond window called the "unguarded interval" where a selector will be on a terminal but it will not be grounded. During this window, another selector could land on the same terminal and attempt to seize it. This was not really a well-understood problem during the 1910s when they were designing this machine, and it proved to not really be an issue for most of its life. However in the 1960s and 1970s as the parts began to age, and fall out of adjustment, the 5-10 ms window became 3 separate intervals, some as long as 50-100 ms. This was a big problem, and required a set of adjustments to be made on the affected selectors. They came up with a test device that could be attached to each selector and identify the ones most seriously affected. Until the issues were corrected, there were many double-connections.
In later common-control machines like the No. 1 and No.5 Crossbars, contention was not only anticipated...it was expected. These machines were designed from the outset with the idea that many pieces of equipment would all be trying to access things at the same time. When a marker (analogous to a CPU) seized a frame, it had to bid for that frame against other markers. When it was awarded access to a switching frame, it had complete control over that frame until it was done. A single operation usually took less than a second, so many markers could access many frames, as long as everything was protected by timers...which it was.
The resistance lamps are used in circuits where there is a large variation in the amount of current that could pass through, but as the current becomes higher, we want to limit it gracefully, until we reach a theoretical maximum and then just hard-limit it. A good example of this is line circuits, which extend out of the building to subscribers' telephones. We provide battery to those phones, and depending on the external loop resistance of their line, there might be a very high, or very low current flow. If the subscriber is close, there will be high current, which we will have to limit. If they are far, there will be lower current, which we do not have to limit quite as much. If their line is shorted out just a few meters from here, there will be *very* high current and we need to hard-limit that.
Hey Sarah, I was wondering, can you explain how the Panel switch actually manages to stop at the correct trunk when it is revertive pulsing? I have always imagined that by the time it sent the revertive pulse, and the far end office told it to stop moving, that it would have already gone past the trunk. Does it have a sort of offset track that causes it to send the RP before it actually makes contact with the trunk?
Good question. I should maybe do a video about this, but I'll try to briefly explain here. Panel offices actually had a physical distance limit between them, partially due to this very problem. The way they got around that was to send the pulses back to the sender *slightly* earlier than the actual moment when the brush was contacting the proper terminal. This allowed for the round-trip time, plus the operate time for the relevant relays. Then, when the power was cut to stop the up-drive, there was a special commutator known as the "C" commutator that kept the circuit closed through itself *just long enough* to make sure that a ratchet at the bottom of the clutch assembly fully locked into its pawl to hold the selector in position. If the alignment of the brushes and commutators was incorrect, it resulted in a wrong connection, so it was very important that they were kept within specified limits. See this page from a switchman's notebook we have: revertive-pulse.tumblr.com/post/151866538129/the-owner-of-this-notebook-is-very-good-at-writing
Sarah great video. Now I am curious as to how "permanent signal" works in the world of digital 'switches". I know what happens in southern California when a phone is off hook, we get the fast loud busy signal through a receiver. If there is a shorted circuit, does the computer generate a ticket for the possible need of repair, or is there still a real person which intercepts and double checks.
Imagine if Cell phones could be "taken of the hook" haha
DandyDon Sarah here. It's almost certain that a computer generates a report that gets looked at by a manager somewhere. With newer switches like the 5ESS, capacity isn't as much of a problem. With the decline of wireline service, most of them are running way under what they can actually support.
Does the load shedding function have any way to respect emergency calls from low priority subscribers? I'm not sure how it could since you'd need the very senders your trying to shed load on to dial the emergency services. Does this pre-date 911?
Nope! After an earthquake or whatever, you change who is allowed to use the phone every 20 minutes. First group A, then B, then C. Then back to A, and so on, until the volume dies down enough that you can have more than one group on at a time. The thinking was that if you had a hard capacity limit, there was no way to tell which calls were genuine emergencies, and which calls were just people calling their friends.
This *does* pre-date 911. The police had a phone number, but it was a regular telephone number just like everyone else. In 1923 they didn't have it all figured out yet :)
@@ConnectionsMuseum Normally Class A (Police, fire, doctors, hospitals, etc) would always have service. Classes B and C would be alternated unless load was very high in which they would both be suspended. Remember also, Line load only affects origination of calls. So if you were on class C and were cut off, your could still receive calls from any other class, but not receive a dial tone.
Right! I misspoke and implies that you’d cut off class A, but that’s not the case.
In movies when there would be a disaster and they'd pick up the phone and get no dial tone, I always just assumed their line was cut. But they could have also been out of senders or line finders. I never thought it would be a capacity problem because I thought dial tone was just connected to everyone's phone all the time when they weren't making a call.
Do the trunks use DX signaling? Two or 4 wire? Or revertive pulse? Maybe DX signaling wasn’t invented when first panel office came on line. Are any subscriber lines ground start capable?
Trunks are 2-wire loop start. No 4-wire, as panel was not capable of toll operation. That would have been handled by operators.
I don't know that any lines were ground start. I see no evidence for that in the schematics, but I haven't looked at all of them. Regular subscriber lines were definitely loop start.
@@ConnectionsMuseum when I was in NYC in 1974, local office 212-WAlker 5 nnnx was panel and we had direct distance dialing. Inter LATA calls must have been handled by #4 office post WWII. Our Sprint (formerly SP Communications) trunks to NY Telephone were mostly 2 or 4 wire DX / e&m. BTW does any of your machines have a 1004 test line and 600 ohm termination? None of these test lines work anymore in the real PSTN
@@sethtaylor5938 Yes, we have 1004 Hz at 232-0003, 832-0003 for the 5XB and 1XB. There's also a sup test line. I have not wired up the silent termination lines yet.
The panel has a flashing busy test line at 722-0099.
@@ConnectionsMuseum BTW where I retired from in NJ 973-540-9971 will get 1004 @ -10 dBm and 540-9966 is 5 seconds of 1004 then 600 ohm quiet term. Also in old legacy VZ ex NJ Bell if u dial 958 (ANAC) on subscribers line in area codes 201, 973, 732 and 908 the switch echoes back the seven digit phone number in a voice message. Kinda unique to old Bell System. Some offices also used 959 especially in Canada. We used that as a trouble shooting tool sometimes at the Main Frame. Telco outside plant used it a lot.
I kinda envy you because you are working on the equipment I first used growing up, and you're around my age. I love this kind of physical electromechanical technology, because the circuits made are actually moving. Unfortunately, I love the internet and the newer technology much more. And as we both know, there was too much noise on the lines I. The HF range to allow this technology to work with each other properly. I was about 6 when they phased out the old crossbar and panel systems in Orlando Florida. My favorite switch was the crossbar 5. I still don't fully understand panel. But I bet I'd love it if I fully understood it. It's like a simplified reverse of the crossbar technology I think (in terms of logic)(maybe parallel to the logic of crossbar).
so interesting about humanity
I got to sit with a test desk tech but it looked very different
Sarah, have any movie productions set in the past ever shot scenes in the museum? It'd be perfect for 'operator' scene.
You NEED modify those circuits for the sender (watch the video)!
Ha B Sender - Motors turned off. What, no motor stop alarm...
Who in the world would downvote this??
And thank you!
Imagine if we made computers with similar moving Technologies. Meaning imagine if we made Dion off computer functions happened Electro mechanically. It would be a huge circuit but it would work much the same but very much very much slower.
We did
Fix them dreads in the front girl! Please!