This represents an invaluable history archive. When all the old technicians and designers will have passed, and all rottening paperwork will have been trashed, these videos will be all that remains of our old telephone system's knowledge. Being a TH-camr myself, I can really appreciate the amount of work you put into these videos. Thank you!
I was a COT that worked on Panel Switching for three years. The knowledge shown in these videos far exceeds the knowledge and expertise that most COTs had at the offices I worked at. We were able to keep 1920s technology clicking along until the early seventies and cutover to ESS.
Your knowledge sir is amazing! Very interesting indeed though I wonder how ever they thought it all out and actually got it all to work in the first place, must have taken them months of head scratching and dead ends. Great video, thank you.
Thank you, and I'm glad you enjoyed it. In North America, it took nearly 30 years (from 1892 to 1920) of continual design changes before things began to settle down to an efficient, reliable and cost effective system. Improvements continued through the decades right up to the 1970's, just as decommissioning of these switches began.
Please consider doing a video that describes how the ANI-B system worked. I can only guess that it somehow used the sleeve lead and/or the other terminal on the top bank of all the connectors. I know that panel switches used a 5300Hz tone on the sleeve lead as part of identifying the calling line. I have no idea if this was the case on SXS switches. Obviously such connectors would connect to an AMAT-type outbound trunk with the relays in the CAMA system generating the MF tones to send the calling party's number forward to the Toll Tandem switch.
Yes, the connector sleeve leads at the distributing frame were cabled to the ANI Number Network and Bus System. I believe the identification tone was 5800Hz. An MF outpulser sent the calling number over the outgoing ANI trunk to the CAMA office. Unfortunately, I don't have documentation or equipment to do a video.
For customers with 10 or less lines, Rotary Hunting connectors were used. The customers would have from 2 to 10 consecutive numbers all associated with the same tens digit.The number listed in the directory would be the one with the lowest units digit. The connector would step the wipers to the dialed number and if it was busy, begin rotary hunting consecutively one terminal at a time. For example, if a customer had a listed station number of 1234 and had 5 numbers, the assigned numbers would be 1234, 1235, 1236, 1237 and 1238. A calling customer would dial 1234 and the connector would step the wipers to terminal 1234. If it was idle , the connection would be made. If it was busy, the wipers would step to 1235, test, and if busy step again to 1236. This would continue until an idle line was found. If all lines were busy, upon reaching the last line, rotary stepping would stop and busy tone would be returned to the caller. For customers with more than 10 lines, Level Hunting connectors were used. This was a much more complex operation, and the connector would receive and store the tens digit before even stepping the wipers at all. The actual level to be hunted on was selectable within each connector in the group and was varied across these connectors to reduce hunting time. That is, each connector could hunt in a different tens digit order to any other. Once a level had been selected, the connector would step the wipers vertically to that level, and then begin rotary hunting consecutively, one terminal at a time.
@@Hicken65 Your videos have been quite interesting. I used to work at a high school that I suspected had 5 inbound lines. The main number ended with 8576 and I knew 8579 and possibly 8570 were also valid. Would it be likely the hunt would go xx76 77 78 79 70? If that is correct you've answered something I've been wondering about over the last 25 years. :)
@@GaryCameron780 Yes, you are correct. The units digits of station numbers on connector bank terminals are all numbered 1, 2, 3, 4, 5, 6, 7, 8, 9 and 0 from left to right and rotary hunting would always be performed in that sequence. Of course, the starting and endpoints were variables that depended on the customer's listed number and number of lines in the hunt group.
My curiosity about a particular aspect of the design keeps coming back into my consciousness. I notice that in the schematic you show of how the phone sets are connected during a conversation, each set has its tip and ring wires routed through a relay to the talk battery and ground. And in each case, both wires go through the relay, as though some engineer who designed it thought there was a reason to balance the circuit. How would the system not function exactly the same way if only tip or only ring were routed through the relay and there were only one winding on the relay? That would seem like a lower-cost solution, but there must be some reason to balance the wires. What is the reasoning here?
This circuitry is a carry over from the talk circuitry used in common battery manual cord switchboards. It is known as the "Condenser-Impedance" circuit. Apparently, the inductive interaction of the two coils increases their impedance to alternating current and at the same time boosts the amplitude of the alternating current undulations, making the sound level at the receiver louder.
@@Hicken65 So, this all suggests that there was an issue installing early Touch-Tone stations on two party lines of this type. If I remember correctly, the early stations didn't have a diode bridge to sort out polarity for power to the touch key circuitry. That also brings up another subject regarding the added equipment to adapt SXS offices for Touch-Tone. Do you happen to have any of those items? Thank for the great videos!
@@bobf.7238 You're right about early WE touch tone dials. They did not have a polarity guard and if the tip and ring leads were reversed the dial would not function. The problem on a 2-party line was that if a subscriber reversed his tip and ring leads, his phone wouldn't ring if someone called him, but his phone would ring if someone called the other party, along with the other party's phone. A number of manufacturer's provided electronic devices to telcos to covert touch tone signals to dial pulses. These were wired in between the line finder and the first selector. The subscriber would pay for the convenience of touch tone push buttons, but the call would still be slow to complete since each digit would still be outpulsed at ten pulses per second into the selectors and connector. I do have one of these devices, but it is not wired into my demo unit.
It's too bad that a "calling party hold" condition always prompted a CO technician to fix the issue. I had been imagining it being used as an early form of DOS attack.
Step-by-step switching systems actually did have an option to be provided with a form of DOS equipment. It was called Line Load Control (LLC). In a disaster or other emergency situation in which the switching system could be overwhelmed with traffic, the telco could turn on the LLC, which could deny originating service to up to 90% of the telephone lines. Lines such as fire, ambulance, police, some government, etc. were assigned as essential lines and not blocked from originating calls. Of course, if someone had an emergency, they would not be able to call for help. For that they would have to go out and find a payphone. Payphone lines were included in the essential category.
Lloydminster, Saskatchewan early 1980s. My cousin's place. I remember him deliberately not hanging up for the pure amusement of annoying the called party. Ah good times.
This represents an invaluable history archive. When all the old technicians and designers will have passed, and all rottening paperwork will have been trashed, these videos will be all that remains of our old telephone system's knowledge. Being a TH-camr myself, I can really appreciate the amount of work you put into these videos. Thank you!
Thanks for your comment. It was a lot of work, but it was very satisfying work that I enjoyed doing.
I was an apparatus man for Ohio bell. What a memory. I changed thousands of wipers.
I changed a few myself. Always good to hear from a fellow CO tech. Thanks for watching.
I was a COT that worked on Panel Switching for three years. The knowledge shown in these videos far exceeds the knowledge and expertise that most COTs had at the offices I worked at. We were able to keep 1920s technology clicking along until the early seventies and cutover to ESS.
I never got to work on Panel, but it looks interesting from the videos I've seen. Thanks for watching.
Your knowledge sir is amazing! Very interesting indeed though I wonder how ever they thought it all out and actually got it all to work in the first place, must have taken them months of head scratching and dead ends. Great video, thank you.
Thank you, and I'm glad you enjoyed it. In North America, it took nearly 30 years (from 1892 to 1920) of continual design changes before things began to settle down to an efficient, reliable and cost effective system. Improvements continued through the decades right up to the 1970's, just as decommissioning of these switches began.
Well done!
wish we had at SMECC a demo unit like that SxS demo setup you have! This is a wonderful tutorial! KUDOS!
Glad you enjoyed it. Thanks for watching.
Please consider doing a video that describes how the ANI-B system worked. I can only guess that it somehow used the sleeve lead and/or the other terminal on the top bank of all the connectors. I know that panel switches used a 5300Hz tone on the sleeve lead as part of identifying the calling line. I have no idea if this was the case on SXS switches. Obviously such connectors would connect to an AMAT-type outbound trunk with the relays in the CAMA system generating the MF tones to send the calling party's number forward to the Toll Tandem switch.
Yes, the connector sleeve leads at the distributing frame were cabled to the ANI Number Network and Bus System. I believe the identification tone was 5800Hz. An MF outpulser sent the calling number over the outgoing ANI trunk to the CAMA office. Unfortunately, I don't have documentation or equipment to do a video.
Thanks for the response. You have a great deal of knowledge and I want to thank you for posting everything you know.
Do you have a video about how ANI finds the calling party?
When this equipment was in service, numbers part of a hunt group had to be consecutive. Correct?
For customers with 10 or less lines, Rotary Hunting connectors were used. The customers would have from 2 to 10 consecutive numbers all associated with the same tens digit.The number listed in the directory would be the one with the lowest units digit. The connector would step the wipers to the dialed number and if it was busy, begin rotary hunting consecutively one terminal at a time. For example, if a customer had a listed station number of 1234 and had 5 numbers, the assigned numbers would be 1234, 1235, 1236, 1237 and 1238. A calling customer would dial 1234 and the connector would step the wipers to terminal 1234. If it was idle , the connection would be made. If it was busy, the wipers would step to 1235, test, and if busy step again to 1236. This would continue until an idle line was found. If all lines were busy, upon reaching the last line, rotary stepping would stop and busy tone would be returned to the caller.
For customers with more than 10 lines, Level Hunting connectors were used. This was a much more complex operation, and the connector would receive and store the tens digit before even stepping the wipers at all. The actual level to be hunted on was selectable within each connector in the group and was varied across these connectors to reduce hunting time. That is, each connector could hunt in a different tens digit order to any other. Once a level had been selected, the connector would step the wipers vertically to that level, and then begin rotary hunting consecutively, one terminal at a time.
@@Hicken65 Your videos have been quite interesting.
I used to work at a high school that I suspected had 5 inbound lines. The main number ended with 8576 and I knew 8579 and possibly 8570 were also valid. Would it be likely the hunt would go xx76 77 78 79 70?
If that is correct you've answered something I've been wondering about over the last 25 years. :)
@@GaryCameron780 Yes, you are correct. The units digits of station numbers on connector bank terminals are all numbered 1, 2, 3, 4, 5, 6, 7, 8, 9 and 0 from left to right and rotary hunting would always be performed in that sequence. Of course, the starting and endpoints were variables that depended on the customer's listed number and number of lines in the hunt group.
My curiosity about a particular aspect of the design keeps coming back into my consciousness. I notice that in the schematic you show of how the phone sets are connected during a conversation, each set has its tip and ring wires routed through a relay to the talk battery and ground. And in each case, both wires go through the relay, as though some engineer who designed it thought there was a reason to balance the circuit. How would the system not function exactly the same way if only tip or only ring were routed through the relay and there were only one winding on the relay? That would seem like a lower-cost solution, but there must be some reason to balance the wires. What is the reasoning here?
This circuitry is a carry over from the talk circuitry used in common battery manual cord switchboards. It is known as the "Condenser-Impedance" circuit. Apparently, the inductive interaction of the two coils increases their impedance to alternating current and at the same time boosts the amplitude of the alternating current undulations, making the sound level at the receiver louder.
So a useful feature of traditional telephone sets is that for talking, they don't care about the polarity of the applied voltage.
That's correct. The tip and ring leads can be reversed on a single party rotary dial telephone and it will still work.
@@Hicken65 So, this all suggests that there was an issue installing early Touch-Tone stations on two party lines of this type. If I remember correctly, the early stations didn't have a diode bridge to sort out polarity for power to the touch key circuitry.
That also brings up another subject regarding the added equipment to adapt SXS offices for Touch-Tone. Do you happen to have any of those items?
Thank for the great videos!
@@bobf.7238 You're right about early WE touch tone dials. They did not have a polarity guard and if the tip and ring leads were reversed the dial would not function. The problem on a 2-party line was that if a subscriber reversed his tip and ring leads, his phone wouldn't ring if someone called him, but his phone would ring if someone called the other party, along with the other party's phone.
A number of manufacturer's provided electronic devices to telcos to covert touch tone signals to dial pulses. These were wired in between the line finder and the first selector. The subscriber would pay for the convenience of touch tone push buttons, but the call would still be slow to complete since each digit would still be outpulsed at ten pulses per second into the selectors and connector. I do have one of these devices, but it is not wired into my demo unit.
I use too circuit test linefinders, selectors, and connectors for GTE from the 1960s to the 1980s.
selectors, and
Always good to hear from a fellow CO tech. Thanks for watching.
It's too bad that a "calling party hold" condition always prompted a CO technician to fix the issue. I had been imagining it being used as an early form of DOS attack.
Step-by-step switching systems actually did have an option to be provided with a form of DOS equipment. It was called Line Load Control (LLC). In a disaster or other emergency situation in which the switching system could be overwhelmed with traffic, the telco could turn on the LLC, which could deny originating service to up to 90% of the telephone lines. Lines such as fire, ambulance, police, some government, etc. were assigned as essential lines and not blocked from originating calls. Of course, if someone had an emergency, they would not be able to call for help. For that they would have to go out and find a payphone. Payphone lines were included in the essential category.
Lloydminster, Saskatchewan early 1980s. My cousin's place. I remember him deliberately not hanging up for the pure amusement of annoying the called party. Ah good times.