In my email notifications from You Tube you had made the following post, which for some reason isn't showing up here: "I'm a data telecomm guy but I find this electro-mechanical stuff fascinating. One step I believe you may have missed describing is how the end of a dial pulse train is detected - I believe it's called the inter digit interval - thus triggering rotation of the switch. Can you illuminate?" I can answer this question for you. The C relay controls this feature, which is described in the video starting at 40:34 and ending at 42:00. The slow release C relay monitors for the end of the dial pulse train. When the A relay has re-operated and remains operated after the end of the last pulse, the C relay releases. The acceptable release time range is from 111 to 140 milliseconds. This closes the energize path for the rotary magnet. Operation of the rotary armature rotates the shaft and wipers to the first terminal of the bank on the selected level. C remains released unless this selector processes another digit in a digit absorbing application. Thanks for watching.
I second Will's posting. Hicken65 explains the core mechanisms of this complex unit rather than trying to gloss over the whole thing, and gives us a clear, coherent and detailed account. This video has increased my understanding greatly.
Thank you so much for explaining the entire mechanism thoroughlly ^^ im an automation engineer and i would have loved too work on these mechanisms! I love how satisfying their mechanism is and how simple the materials in it are. Im amazed about how neatly designed metal and isolators can acomplish a fully automatic connection selection! Great video!
I think that probably most CO technicians of the electromechanical era thoroughly enjoyed working on this equipment. I know I did. I'm glad you enjoyed the video and thanks for watching.
These equipments are so familiar ,I have 38 years of experience in maintaning their proper operation , maintenence , adjustment and good service to more than 25 thousand subcribers in aulto automatic exchange.Itill cherish those days.
Well, it's always great to hear from a fellow switchman. It seems that most of us who worked on this equipment have fond memories . Thanks for watching.
Wow, Thanks for making this video! I managed to get my hands on an ED-31933 Selector a little while ago. Thanks to this video, your comments on the video, and a few documents found in the TCI library, I've managed to make it seize, step, hunt, and release when hooked up to a rotary phone! I'm still trying to figure out how I should go about simulating a down-stream connector so that it can connect to another phone and release on hang up, but this video has given me a great head start.
Well, I'm glad I could be of some help to you. I encourage you to keep looking for a connector switch to hook into your system, along with a ringing generator and perhaps a line finder. In case you're not aware, I have videos on the line finder and connector on my channel. Just search "hicken65" on UA-cam. Thanks for watching.
Superb video. The visual detail and clarity of description was excellent. I wondered about the leads that attached to the moving wipers - what are they made of that allowed them to reliably endure all that movement? Also, the sparking in one of the contacts of the A-relay during pulse transmission must have made for a short contact life. Many thanks for posting, most informative.
Thank you for taking the time to reply. I have always had an interest in electro-mechanical devices since I started out servicing teleprinters early in my career. Looking forward to part 2. Best wishes.
this video is cool!! quick question though, in a large telco office when they housed heaps of the line finders, how did they set the system up so a free line finder could be found if some other ones were in use at the time the handset was lifted? i ask because i imagine having the subscriber connected to one line finder in an office that was serving thousands of lines would be troublesome since if they were only connected to one line finder then that line finder could quite often be busy. would you also happen to know how a line finder searched for a free first selector from a large group of first selectors? thats the part i cant seem to figure out also, thanks!
There were 100 lines assigned to twenty line finder switches. A rotary switch would select the next idle line finder so when a customer picked up, their line was found. If you notice the banks of contacts were 10 high with 10 contacts per bank. A large office would have row after row, usually 11 feet high bays of line finders. Hope this answers your question.
Let me update Glenn's reply. A line finder group would have 200 lines circuits. If you can find a photo of a mounted Line finder you would see three sets of contact banks(see time 26:45). One more than a selector or connector bank. Any Line finder could provide dial tone to any of the 200 lines in the group. if any 20 lines in the group made and were in a call at the same time, none of the other 180 lines could get dial tone to made a call until one or mare of the calls were released. This gave a concentration of 10 to 1. The 180 Lines could still receive calls just not make them. This was for a 1SXS office. I worked for three months in a Customer Centrex were there were 32 line finders in a line finder group. My work in SXS was from 1970 to 1977 I still have dreams about the equipment.
Good content but need a camera capable of useful slo-mo. Do you have a link to a site with annotated schematics to show the circuits through the various contacts?
There is a site that has the schematic drawing and a printed circuit description. Go to www.telephonecollectors.org Select TCI Library. Look at the “Browse The Library” list and scroll to “BC Switching Library”. On that list, scroll to and select “Western Electric”. On the Western Electric Categories page, scroll down to and select “SD-CD-30976-01 3 4 Wire Selector”. On the Selector page, the first item is the circuit description. Click on “view” on the extreme right hand side of that item and a PDF of the Circuit Description will appear. The third item on the Selector page is the schematic drawing. Again, click on “view” for that item and a PDF of the schematic drawing will appear.
The best explanation on youtube. Can you tell me what each of the 8(16) blades in the wooden block are for (wiring diagram) and are they the same on a selector, line finder and connector? Thanks
That's called a plug. It has 16 blades or prongs arranged in 8 pairs.It's called a plug because it plugs into 8 pairs of jack springs mounted on the switch frame. This is shown in the video.This allows the selector to be a plug and play device without having to undo any wires. So all external wiring coming into the selector is handled by this plug and jack spring arrangement. This includes dc power, ground, tones, preceding circuits, etc. The one exception is succeeding circuits which are connected through the wipers and bank terminals. The line finder also has a 16 prong plug, while the connector has a 24 prong plug.
@@Hicken65Thanks for the quick response. Would like to know what each and everyone does on your selector at 11:05, it looks like there is 10 blades used and 12 wires or so.
@@SuperYmymym You’re looking at the plug on my parts switch, which is not the same type of switch working on my demo unit, so its wiring has no significance in regards to how my demo unit functions. However, the physical prong arrangement is exactly the same. Here’s how the prongs are numbered, viewing from the rear side of the switch. From left to right the 16 prongs are numbered 16, 14, 12, 10, 8, 6, 4, 2, 1, 3, 5, 7, 9, 11, 13 and 15. On my demo unit, prongs 16, 8, 6, 4, 3, 7, and 13 are unused; prong 14 is for busy tone; prongs 12, 10 and 5 are for -48-volt battery supply; prong 2 is for the tip transmission wire from the preceding circuit; prong 1 is for the ring transmission wire from the preceding circuit; prong 9 is for the sleeve control wire from the preceding circuit; prongs 11 and 15 are for the ground supply (except on the 1st selector, where prong 15 is for the dial tone supply). From the prongs, the wires go to various places inside the selector, generally relay windings or relay contacts, none of which would be of any use to you without a copy of the wiring diagram. I hope this helps with whatever you’re looking for.
Thanks for putting the video together, great content and very detailed. I was able to get a similar selector to the one you have in the video. I would like to power it up and hook up a rotary phone to watch it run. Can you provide additional information of how you hooked up your demo unit (I assume using the 16 blades in the back?). I would like to know where you connected the power (48V DC?) and where the colored wires from the rotary phone would connect? Also, unfortunately my selector did not come with a Bank Assembly. Any idea where I could get one?
Here’s how the prongs (blades) are numbered, viewing from the rear side of the switch. From left to right the 16 prongs are numbered 16, 14, 12, 10, 8, 6, 4, 2, 1, 3, 5, 7, 9, 11, 13 and 15. On my demo unit, prongs 12, 10 and 5 are for -48-volt battery supply; prongs 11 and 15 are for the ground supply; prongs 1 and 2 are for the ring and tip transmission wires from the preceding circuit, which in your case would be the two wires from the rotary dial telephone set. As for getting a bank assembly, I would suggest you reach out to members of the Telephone Collectors International. They have a website and a listserve (forum) where you could ask if anyone had a bank you could purchase. Thanks for watching.
That’s just what I was looking for - thanks so much for the quick response! I remember back in the 1970s my parents getting a detailed itemized phone bill each month. How did the phone company track the number dialed and the duration of the call to send out the bill? Just curious if it was a separate system, or somehow integrated with this equipment?
@@MsBSBrown Prior to Direct Distance Dialing (DDD), customers dialed “0” to place a long distance call. The billing was accomplished by the long distance switchboard operators who made up call detail tickets which were then sent to the accounting department. With the advent of DDD in the 1950’s, billing was performed by electromechanical devices that collectively were known as Automatic Message Accounting (AMA) equipment. This equipment was installed at the toll switching centres. AMA equipment would identify the calling telephone number, and record that number, the called number, the start time of the call, the end time of the call, and other miscellaneous information by making coded perforations on a reel of paper tape. Each day, these AMA tapes would be sent to the telco's accounting department which had equipment to read the tapes and store the call details for the preparation of the monthly bills. SXS end offices were equipped with adjunct equipment called Automatic Number Identification (ANI) that forwarded the calling telephone number to the AMA equipment at the toll centre.
We have the selector hooked up to power as described - if the wiper arms are lifted, the release relay engages. However a phone attached to 1 and 2 is never able to seize it - in fact there is no voltage on these pins. The A relay never energizes. Any ideas? Are there any schematics of these things available?
The white sleeve located behind the shaft spring that runs up/down on the normal post has bumps on its sides which appear to operate some other contacts. What is the purpose of these? They look like they could detect particular vertical positions.
So the A relay's coil doesn't have such a high inductance that it would suppress the highest-frequency component of the dial tone (as one could find by subjecting the dial tone to Fourier analysis and looking for the highest-frequency component).
I don't think it mattered much. As long as the caller received some sort of a buzzing sound.There wasn't any one standard for the make up of dial tone in the early days. Different manufacturers of tone generators had different tones.
Well, I can't speak to all selector types, because I don't have the information. The particular selector type I am using in my demo unit, which is SD-30976, could be used in No.1, 350A, 355A, 356A, and 360A offices.
@@gpwgpw555 Well, the SD 30200 was certainly a commonly used selector. However, it does not have any digit absorbing functionality. Its use as a first selector was replaced by the SD 30976 in many offices when 7 digit dialing was introduced in the late 1940's. The digit absorbing feature of the SD 30976 permitted 7 digit dialing without having to build up the switch train. The replaced SD 30200 switches, were retained to handle growth on other selector ranks.
What is the purpose of that top finger or "head" part of the stationary dog? It doesn't seem to engage with anything. BTW it might amuse you to note that hurdy-gurdies (stringed musical instruments that use a wheel to vibrate the strings) are also equipped with dogs.
When vertical stepping has ended and rotary stepping begins, the vertical support for the shaft is transferred from the top leg of the double dog to the top leg of the stationary dog.This is necessary to provide for a smooth rotating motion of the wipers.The vibrations of the double dog during rotation (caused by the double dog's lower leg's ratcheting actions on the rotary ratchet) would otherwise interfere with this. The stationary dog maintains this support for the call duration. Then, on release of the switch, the stationary dog provides the vertical support during the anticlockwise rotation of the shaft to its horizontal rest position. At that point the stationary dog leg is back in the vertical ratchet channel and the shaft can drop down to its home position.
Well, a large office serving 50,000 lines in a downtown business district was rather loud. I never considered it to be noisy, however. To me, it was always music to my ears.
I'm a data telecomm guy, and this electro-mechanical switching is what we used to call FM - freaking magic! Great video.
In my email notifications from You Tube you had made the following post, which for some reason isn't showing up here: "I'm a data telecomm guy but I find this electro-mechanical stuff fascinating. One step I believe you may have missed describing is how the end of a dial pulse train is detected - I believe it's called the inter digit interval - thus triggering rotation of the switch. Can you illuminate?" I can answer this question for you. The C relay controls this feature, which is described in the video starting at 40:34 and ending at 42:00. The slow release C relay monitors for the end of the dial pulse train. When the A relay has re-operated and remains operated after the end of the last pulse, the C relay releases. The acceptable release time range is from 111 to 140 milliseconds. This closes the energize path for the rotary magnet. Operation of the rotary armature rotates the shaft and wipers to the first terminal of the bank on the selected level. C remains released unless this selector processes another digit in a digit absorbing application. Thanks for watching.
This is without a doubt the best explanation anywhere online of how these switches operate and are assembled. Thank you for posting.
Thank you for your kind remarks.
I second Will's posting. Hicken65 explains the core mechanisms of this complex unit rather than trying to gloss over the whole thing, and gives us a clear, coherent and detailed account. This video has increased my understanding greatly.
Thank you so much for explaining the entire mechanism thoroughlly ^^ im an automation engineer and i would have loved too work on these mechanisms! I love how satisfying their mechanism is and how simple the materials in it are. Im amazed about how neatly designed metal and isolators can acomplish a fully automatic connection selection! Great video!
I think that probably most CO technicians of the electromechanical era thoroughly enjoyed working on this equipment. I know I did. I'm glad you enjoyed the video and thanks for watching.
These equipments are so familiar ,I have 38 years of experience in maintaning their proper operation , maintenence , adjustment and good service to more than 25 thousand subcribers in aulto automatic exchange.Itill cherish those days.
Well, it's always great to hear from a fellow switchman. It seems that most of us who worked on this equipment have fond memories . Thanks for watching.
I think weekly starting pay for a COT in 1968 was $87.
Very descriptive, clear, and interesting video! Many thanks for the posting it
Glad you enjoyed it. Thanks for watching.
I double-dog dare anyone to dislike this video. Very interesting, informative, and entertaining. Much thanks to Hicken65.
Well thanks. I think my work here is done.
Wow, Thanks for making this video! I managed to get my hands on an ED-31933 Selector a little while ago. Thanks to this video, your comments on the video, and a few documents found in the TCI library, I've managed to make it seize, step, hunt, and release when hooked up to a rotary phone! I'm still trying to figure out how I should go about simulating a down-stream connector so that it can connect to another phone and release on hang up, but this video has given me a great head start.
Well, I'm glad I could be of some help to you. I encourage you to keep looking for a connector switch to hook into your system, along with a ringing generator and perhaps a line finder. In case you're not aware, I have videos on the line finder and connector on my channel. Just search "hicken65" on UA-cam. Thanks for watching.
Superb video. The visual detail and clarity of description was excellent. I wondered about the leads that attached to the moving wipers - what are they made of that allowed them to reliably endure all that movement? Also, the sparking in one of the contacts of the A-relay during pulse transmission must have made for a short contact life. Many thanks for posting, most informative.
Thank you for taking the time to reply. I have always had an interest in electro-mechanical devices since I started out servicing teleprinters early in my career. Looking forward to part 2. Best wishes.
this video is cool!!
quick question though, in a large telco office when they housed heaps of the line finders, how did they set the system up so a free line finder could be found if some other ones were in use at the time the handset was lifted? i ask because i imagine having the subscriber connected to one line finder in an office that was serving thousands of lines would be troublesome since if they were only connected to one line finder then that line finder could quite often be busy.
would you also happen to know how a line finder searched for a free first selector from a large group of first selectors? thats the part i cant seem to figure out also, thanks!
There were 100 lines assigned to twenty line finder switches. A rotary switch would select the next idle line finder so when a customer picked up, their line was found. If you notice the banks of contacts were 10 high with 10 contacts per bank. A large office would have row after row, usually 11 feet high bays of line finders. Hope this answers your question.
Let me update Glenn's reply. A line finder group would have 200 lines circuits. If you can find a photo of a mounted Line finder you would see three sets of contact banks(see time 26:45). One more than a selector or connector bank. Any Line finder could provide dial tone to any of the 200 lines in the group. if any 20 lines in the group made and were in a call at the same time, none of the other 180 lines could get dial tone to made a call until one or mare of the calls were released. This gave a concentration of 10 to 1. The 180 Lines could still receive calls just not make them. This was for a 1SXS office. I worked for three months in a Customer Centrex were there were 32 line finders in a line finder group. My work in SXS was from 1970 to 1977 I still have dreams about the equipment.
Thnku sir...thi is very helpful 😁
You're welcome and thanks for watching.
Good content but need a camera capable of useful slo-mo. Do you have a link to a site with annotated schematics to show the circuits through the various contacts?
There is a site that has the schematic drawing and a printed circuit description.
Go to www.telephonecollectors.org
Select TCI Library. Look at the “Browse The Library” list and scroll to “BC Switching Library”. On that list, scroll to and select “Western Electric”. On the Western Electric Categories page, scroll down to and select “SD-CD-30976-01 3 4 Wire Selector”. On the Selector page, the first item is the circuit description. Click on “view” on the extreme right hand side of that item and a PDF of the Circuit Description will appear. The third item on the Selector page is the schematic drawing. Again, click on “view” for that item and a PDF of the schematic drawing will appear.
The best explanation on youtube. Can you tell me what each of the 8(16) blades in the wooden block are for (wiring diagram) and are they the same on a selector, line finder and connector? Thanks
That's called a plug. It has 16 blades or prongs arranged in 8 pairs.It's called a plug because it plugs into 8 pairs of jack springs mounted on the switch frame. This is shown in the video.This allows the selector to be a plug and play device without having to undo any wires. So all external wiring coming into the selector is handled by this plug and jack spring arrangement. This includes dc power, ground, tones, preceding circuits, etc. The one exception is succeeding circuits which are connected through the wipers and bank terminals. The line finder also has a 16 prong plug, while the connector has a 24 prong plug.
@@Hicken65Thanks for the quick response. Would like to know what each and everyone does on your selector at 11:05, it looks like there is 10 blades used and 12 wires or so.
@@SuperYmymym You’re looking at the plug on my parts switch, which is not the same type of switch working on my demo unit, so its wiring has no significance in regards to how my demo unit functions. However, the physical prong arrangement is exactly the same. Here’s how the prongs are numbered, viewing from the rear side of the switch. From left to right the 16 prongs are numbered 16, 14, 12, 10, 8, 6, 4, 2, 1, 3, 5, 7, 9, 11, 13 and 15. On my demo unit, prongs 16, 8, 6, 4, 3, 7, and 13 are unused; prong 14 is for busy tone; prongs 12, 10 and 5 are for -48-volt battery supply; prong 2 is for the tip transmission wire from the preceding circuit; prong 1 is for the ring transmission wire from the preceding circuit; prong 9 is for the sleeve control wire from the preceding circuit; prongs 11 and 15 are for the ground supply (except on the 1st selector, where prong 15 is for the dial tone supply). From the prongs, the wires go to various places inside the selector, generally relay windings or relay contacts, none of which would be of any use to you without a copy of the wiring diagram. I hope this helps with whatever you’re looking for.
@@Hicken65 Perfect, thanks
Thanks for putting the video together, great content and very detailed. I was able to get a similar selector to the one you have in the video. I would like to power it up and hook up a rotary phone to watch it run. Can you provide additional information of how you hooked up your demo unit (I assume using the 16 blades in the back?). I would like to know where you connected the power (48V DC?) and where the colored wires from the rotary phone would connect?
Also, unfortunately my selector did not come with a Bank Assembly. Any idea where I could get one?
Here’s how the prongs (blades) are numbered, viewing from the rear side of the switch. From left to right the 16 prongs are numbered 16, 14, 12, 10, 8, 6, 4, 2, 1, 3, 5, 7, 9, 11, 13 and 15. On my demo unit, prongs 12, 10 and 5 are for -48-volt battery supply; prongs 11 and 15 are for the ground supply; prongs 1 and 2 are for the ring and tip transmission wires from the preceding circuit, which in your case would be the two wires from the rotary dial telephone set. As for getting a bank assembly, I would suggest you reach out to members of the Telephone Collectors International. They have a website and a listserve (forum) where you could ask if anyone had a bank you could purchase. Thanks for watching.
That’s just what I was looking for - thanks so much for the quick response!
I remember back in the 1970s my parents getting a detailed itemized phone bill each month. How did the phone company track the number dialed and the duration of the call to send out the bill? Just curious if it was a separate system, or somehow integrated with this equipment?
@@MsBSBrown Prior to Direct Distance Dialing (DDD), customers dialed “0” to place a long distance call. The billing was accomplished by the long distance switchboard operators who made up call detail tickets which were then sent to the accounting department. With the advent of DDD in the 1950’s, billing was performed by electromechanical devices that collectively were known as Automatic Message Accounting (AMA) equipment. This equipment was installed at the toll switching centres. AMA equipment would identify the calling telephone number, and record that number, the called number, the start time of the call, the end time of the call, and other miscellaneous information by making coded perforations on a reel of paper tape. Each day, these AMA tapes would be sent to the telco's accounting department which had equipment to read the tapes and store the call details for the preparation of the monthly bills. SXS end offices were equipped with adjunct equipment called Automatic Number Identification (ANI) that forwarded the calling telephone number to the AMA equipment at the toll centre.
Very informative - thank you for the response and putting your videos on UA-cam!
We have the selector hooked up to power as described - if the wiper arms are lifted, the release relay engages. However a phone attached to 1 and 2 is never able to seize it - in fact there is no voltage on these pins. The A relay never energizes. Any ideas? Are there any schematics of these things available?
The white sleeve located behind the shaft spring that runs up/down on the normal post has bumps on its sides which appear to operate some other contacts. What is the purpose of these? They look like they could detect particular vertical positions.
Never mind, it is explained in part 2 of this video...
You need to watch part 2. Just search my channel name, Hicken65, on You Tube and look for The Selector In the Step-by-step Switching System Part 2.
So the A relay's coil doesn't have such a high inductance that it would suppress the highest-frequency component of the dial tone (as one could find by subjecting the dial tone to Fourier analysis and looking for the highest-frequency component).
I don't think it mattered much. As long as the caller received some sort of a buzzing sound.There wasn't any one standard for the make up of dial tone in the early days. Different manufacturers of tone generators had different tones.
My first job ever was adjusting these kind of switches on a Siemens no 17 type exchange.
Always good to hear from a former SXS switchman. Thanks for watching.
Hi, I have an ED-55062 selector available to me. Is this also a toll selector? Any chance of a circuit digram?
Yes, this is a SXS Combined Intertoll and Toll Transmission Selector. No drawings are available that I am aware of.
Were there any differences in the selectors that were used in a No. 1 SXS, vs a 355 Step CDO?
Well, I can't speak to all selector types, because I don't have the information. The particular selector type I am using in my demo unit, which is SD-30976, could be used in No.1, 350A, 355A, 356A, and 360A offices.
Thank you for the reply. That answered my curiosity. Keep up the great work!!
The SD-30200 was the Type we had in our offices. It looked and worked just like the SD30976. and it was basically wired the same way.
@@gpwgpw555 Well, the SD 30200 was certainly a commonly used selector. However, it does not have any digit absorbing functionality. Its use as a first selector was replaced by the SD 30976 in many offices when 7 digit dialing was introduced in the late 1940's. The digit absorbing feature of the SD 30976 permitted 7 digit dialing without having to build up the switch train. The replaced SD 30200 switches, were retained to handle growth on other selector ranks.
What is the purpose of that top finger or "head" part of the stationary dog? It doesn't seem to engage with anything.
BTW it might amuse you to note that hurdy-gurdies (stringed musical instruments that use a wheel to vibrate the strings) are also equipped with dogs.
When vertical stepping has ended and rotary stepping begins, the vertical support for the shaft is transferred from the top leg of the double dog to the top leg of the stationary dog.This is necessary to provide for a smooth rotating motion of the wipers.The vibrations of the double dog during rotation (caused by the double dog's lower leg's ratcheting actions on the rotary ratchet) would otherwise interfere with this. The stationary dog maintains this support for the call duration. Then, on release of the switch, the stationary dog provides the vertical support during the anticlockwise rotation of the shaft to its horizontal rest position. At that point the stationary dog leg is back in the vertical ratchet channel and the shaft can drop down to its home position.
In a large building full of this equipment it had to get rather noisy at times.
Well, a large office serving 50,000 lines in a downtown business district was rather loud. I never considered it to be noisy, however. To me, it was always music to my ears.