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.

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.

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.

Glad you enjoyed it. Thanks for watching.

Well thanks. I think my work here is done.

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.

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 KZfaq. Thanks for watching.

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.

Always good to hear from a former SXS switchman. Thanks for watching.

You're welcome and thanks for watching.

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.

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

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.

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.

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 KZfaq!

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?

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.

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.

Yes, this is a SXS Combined Intertoll and Toll Transmission Selector. No drawings are available that I am aware of.

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.

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.