The Rotary Dial In The Step by Step telephone Switching System

[@shaggydogg3786]

The whole story of the bell system seems to me that the engineers were just one step ahead of demand. It is a truly fantastic story to say the least and your videos are the best. We have a microwave AT&T tower near our farm in southern Illinois that has been there since before I was born. ( I’m 60 btw) and I think it has been long decommissioned. It would be interesting if you could do a video on the various trunk lines and long distance systems. Thanks again for another great video.

[@Hicken65]

You should check the AT&T archives on You Tube for transmission videos. One that comes to mind is titled "The Far Sound". I'm glad you have enjoyed my videos. Thanks for watching.

[@kensmen7701]

Thank you for posting this. I’ve been struggling with a WE #6C not dialing out. Your speaking skills are outstanding. Along with the slow-mo ...You taught, what was a mystery to me for years ...very understandable.

[@Hicken65]

Well, I'm glad my video was helpful to you and thanks for watching.

[@viktordubowskii695]

The governor plays an important role, because if the speed of the pules isn't timed right you get a number that's wrong, not what you dialed. I ran into that problem calling people I didn't intend on calling. Loved your video. It helped.

[@Hicken65]

You're right about the importance of the governor. Glad you enjoyed the video and again, thanks for watching.

[@flippert0]

An absolute eye opener, thanks for putting this together!

[@Hicken65]

You're welcome and thanks for watching.

[@nehatutorials3723]

Sir, I am so thankful to you for this explanation. Thank you so much.

[@Hicken65]

You are most welcome. Thanks for watching.

[@nehatutorials3723]

@@Hicken65 u r a great tr. Thank you so much for replying 😊

[@viktordubowskii695]

Thank you for the upload, this helped me fix my rotary phone, I had a problem with the bell not ringing, because there was corrosion on the contacts for the bell to receive current.

[@Hicken65]

You're welcome and thanks for watching.

[@bobf.7238]

When I was a teenager, I spent a summer in Petersburg, VA where the Bell System was market testing Touch-Tone. When I moved back to Los Angeles, around 1965, I was impatient with how long it took to place a call with a rotary dial. It turns out that Pacific Telephone (PT&T) had just upgraded our C.O. to cross bar. Guess What, you can remove the governor springs and the dial will whip back very quickly. The cross bar originating register never missed a beat. Ahhh, Teenage mischief.

[@Hicken65]

I love telephony anecdotes like yours. I know that the Number 5 Crossbar Dial Pulse Originating Register was designed to handle at least 20 pulses per second. Thanks for watching.

[@markrgreenlane]

On the A relay, why does it have two windings instead of just one like a normal relay, also how does the selector know that the dialled number has completed to then start the hunt for the idle trunk?

[@Hicken65]

The outside plant cable pairs are subject to a great deal of signal loss due to the amount of capacitance built up along their length. They are also subject to noise interference from external sources, leakage, poor insulation, etc.. Keeping the two wires balanced by inductance coils along their length and at their termination points at the central office minimizes the noise interference and signal losses. As a result, the dial pulses are stronger and cleaner than if an imbalanced line with a single coil winding on one side and direct ground on the other side was utilized. The C relay on the selector monitors the incoming pulses. It is a slow release relay and remains operated while the loop is opening and closing as the pulses are being sent. When all the pulses of a particular digit have been sent, the loop closes and remains closed until the next set of pulses begin to be sent. This interdigital interval allows sufficient time for the C relay to release, which initiates the start of rotary trunk hunting.

[@michaelcostello6991]

What makes the wiper rotate to find a free trunk line ? How does it know its a free line. Thanks for great video. Really interesting.

[@Hicken65]

Everything you want to know is answered in my long video "The Selector In The Step-By-Step Telephone Switching System Part 1". Just search my channel name "hicken65" in You Tube. Thanks for watching.

[@gelpaks]

Can a Northern electric 6a dial be wired into a 302 western electric rotary phone?

[@Hicken65]

Yes. In the days that these sets and dials were being manufactured, Northern Electric manufactured them under a licensing arrangement with Western Electric. As such, the NE and WE 302 sets and 6A dials are identical.

[@gelpaks]

@@Hicken65 well....when I wire it in, everything works correctly except the receiver. I can't hear dial tone unless I pull down on the dial just a bit like I'm starting to dial. I can dial out n connect to another caller but I can't hear them unless I keep the dial pulled down. When I let go, I can't hear them but they can still hear me. The problem is not about the type of dial I'm installing?

[@Hicken65]

@@gelpaks The problem is not the type of dial. However, the dial itself could be faulty. Most likely though, there is a wiring error. Inside the dial, there is a receiver shunt that opens when the dial is off-normal and a transmitter shunt that closes when the dial is off-normal. It seems as though the wiring between the transmitter and receiver in the handset and the dial connections are reversed somewhere. Here is a link to the wiring diagram. Ensure that every wire in your handset, dial, induction coil and capacitor are exactly as shown in the diagram. etler.com/docs/bsp-archive/502/502-400-401CA_IC.pdf

[@gelpaks]

@@Hicken65 Thank you for the wiring schematic! I'm much more a picture type person but I'll do my best to figure out the schematic in relation to the phone wiring. Here's my confusion though, and why this seems like such an odd issue, the transmitter in the handset works fine and the person I call can hear me regardless of the position of the dial. It's just the receiver that's the issue. If the wiring is reversed, wldnt it be in the dial and where the white (receiver) wire connects? This phone also works just as it should with the blank wired in. Also the dial has 6 screws to attach the wires to and not 5. There is a BK and a BL connection, when other 6a dials (specifically western electric brand) have only 5. Does that make a difference?

[@Hicken65]

@@gelpaks So a No. 6 dial with 6 terminals, which includes a BL terminal is not really a No. 6A dial. It could be any one of the following types: 6J, 6K, 6L or 6S. This dial is not meant to work in a type 302 telephone set because the contacts between terminals BB and W are open when the dial is normal and closed when the dial is off-normal, which is the direct opposite of their operation in a 6A dial. You might be able to make it work by connecting a shorting wire between dial terminals W and BB. The receiver will be quite noisy during dialing. Good luck with this. Let me know if it works.

[@michaelbenardo5695]

How did you get a dial with only 5, rather than 6, contacts to work with a 302?

[@Hicken65]

An astute observation, indeed! I used the #2 dial throughout the video because of its wonderful clickety-clack sound that is lacking in later dials. However, when you see the split screen of the #2 dial on a type 302 housing causing the selector switch to vertically step upwards, well, it didn't really happen that way. I just videoed the #2 dial rotating in an empty type 302 shell. The actual switch stepping was caused by the # 6 dial shown on the type 302 set with the BEechwood 4-5789 telephone number. Thanks for watching.

[@Donald-df9fc]

GTE made the best rotary phone dials. They were made at Automatic Electric.

[@andyblackpool]

Hi again. Can you confirm where the fast pulses originate during in the intra digital interval that move the wipers horizontally through the contacts when searching for access trunks to the next range of selector? Am I correct in thinking a solenoid pulling in and moving the wiper one step horizontally and if the wiper hits a contact that's earthed (grounded) it pulls a relay that closes a contact again to the solenoid to move it one more step along until it finds one that's not earthed which it then latches onto it, is this right; a bit like the make/break contacts on the clanger of a standard door bell? ...think I may have worked out the answer to my own question here (or seen it subconsciously already in one of your other videos) but would appreciate conformation how this actually happens if you could oblige please? Cheers and thanks very much. Andy

[@Hicken65]

Yes, you're absolutely correct! The process is detailed in my video "The Selector InThe Step-By-Step Telephone Switching System Part 1". It's a long video, so if you just want to see the rotary hunting section, cut in at the 41 minute mark.

[@andyblackpool]

Thanks, I watched this video the other day but I fear my sponge brain isn't as absorbent as it was a couple of decades ago though I'm pleased to say all is (mostly) on board now; have just re watched this fascinating video and feel much more confident about my understanding now. I visited a telephone exchange (as we call them) on a school trip as a 10 year old - mid 60's - and always having an interest in everything electrical and mechanical was instantly hooked with the sounds and the movements. Thank goodness for KZbin and people like yourself getting this stuff all on record for people like me. Once more thank you for this.

[@Hicken65]

It is for people like you that I make these videos. Thanks for watching.

[@Hicken65]

I'm always fascinated by inventions that gave us the earliest practical applications of electricity. I can only imagine the delight Strowger must have felt when his brilliant team finally built the reliable switch that he had envisioned in 1889, and then made it suitable for public use with the rotary dial. It's difficult to find good documentation on the early telephony inventions. Thanks for your comments and thanks for watching.

[@paulromsky9527]

I won a bet in the US Air Force in the 1980's that I could call someone on base and not touch the dial. I have good timing so I just clicked the hang up button rapidly to mimic the rotary speed and pulses for each digit with a short delay after each digit. This works on most touch tone lines as well. I won another bet that I could call someone without me touching the phone. All I asked it that someone pick up the handset off the hook and place it on the table in front of the phone. Then using my Yamaha DX7 synthesizer (that had pre programmed) I sounded each dual tone for each digit in the number and the call went through. Technically if two people can whistle the two tones for each digit perfectly they can dial a number that way. Also, in the 1980's film "War Games", Mathew Broderick simply removes the lower part of a pay phone hand set by tapping it on a hard surface and then simply unscrewing it. No, it's not that simple and special tools are required to remove those handset covers on payphones. Then he proceeds to get a trunk line for free by using an old pull off top from a tin can. He simply shorts out the two contacts from the removed microphone a few times until he mimics the signal for a trunk line and dial tone. No, the filter network does not allow shorting/opening of the 600 Ohm phone line signal, nor can a noisy signal from the microphone section generate the required tones, and especially not after the phone hacker "Captain Crunch" used a toy whistle from a cereal box to generate the two simultaneous tones required (at the time) to get a trunk line - the phone companies made that more complicated years before the movie when they found about the simple hack. Can you elaborate on this?

[@Hicken65]

Flashing the switch hook opens and closes the loop through the telephone set in the same way as the rotary dial. The rotary dial does it in a consistently timed fashion and with a particular percent break/make of around 60/40 percent. Flashing the switch hook requires good timing in order to reach the correct number, but is readily accomplished with practice. Any device that can generate the same tones as the touch tone telephone can be used to place a call if the device is close enough to the transmitter. In the "War Games" movie, the pay phone used is a Bell System 3-slot rotary dial payphone arranged for prepay service. This means it would be configured for ground start to get dial tone. The phone is connected by two wires (tip & ring) to the central office (CO). The ring wire is connected to one side of a line relay winding at the CO. The other side is of the winding is connected to negative 48-volt battery. So a ground on the ring wire at the payphone will operate the line relay. An operated line relay initiates a series of events at the CO to supply dial tone to the line. The payphone housing is always grounded to protect users from foreign voltages. Both the receiver and transmitter contacts in the handset are connected through the payphone’s internal wiring to the ring wire. So touching the grounded housing with one end of the pull-tab and the other end to the exposed transmitter contact would apply ground to the ring wire, and dial tone would be heard in the receiver. Ground is normally supplied through a pair of contacts that are closed when the pay phone hopper trigger is deflected by depositing a coin. The deflected hopper trigger also removes a short circuit across the dial contacts. Since no coin was deposited, the short across the dial remains and dialing would be ineffective. So, in this case, Broderick would get dial tone but he wouldn’t be able to dial out using the rotary dial. He could have attempted switch hook flashing. He wasn't trying to hack into the long distance trunk network. He just wanted local dial tone, after which he rotary dialed the number for long distance information (1+ area code+555-1212). Serious phone phreaking began in the 1960's and continued well into the 1980's. This involved building devices that emulated all the analog signals used in the long distance network. The evolution away from an analog multifrequency in-band signalling took a very long time to complete, before blue boxes became obsolete. If you are interested in this subject matter, I can recommend an excellent book titled "Exploding The Phone" by Phil Lapsley.

[@paulromsky9527]

@@Hicken65I am a musician with some Morse code experiance, so tapping out 60/40 % Duty cycle sequences at about 10Hz was easy for me with virtually no practice - I just mimicked the tempo from the listening to the rotary dial clicking. You obviously must have been amused by that telephone scene in the film when you first saw it. Wow, ok, so he could have gotten a dial tone with that phone after all. One would think the network/filter circuitry in the phone would prevent hand set shorting from controlling the tip/ring opening/closing the loop. But pay phone hand sets are very, very, difficult to break, how did he open the cover so easily? I could never find a way to open a pay phone handset - even with oversized channel lock pliers.

[@paulromsky9527]

@@Hicken65 I will see if my library has that book. I heard that ALL telephones are actually bugging devices. Even if the phone is hung up, a very high gain amplifier can be connected between the tip and ring lines anywhere between the extension and CO. This allows the bugging of criminals (and even the public) without having to get in the building (or even get a wiretap warrant). In the Air Force, our shop was so classified that a special relay external to the phone (mounted on the wall next to the phone) totally isolated the tip and ring wires that led back the CO. When we picked up the handset, inside that box, a relay clicked, and a red light came on to let us know the phone was now connected to the line and to not have classified conversations in the background. The ringer was inside the box, and relayed only the high voltage to the phone's ringer when a call came in. I open it up once to reverse engineer it... it was a very clever device. This prevented our phone from becoming a bugging device as it is designed to be and prevent electronic signals from our equipment being coupled into the lines from the network/filters/earpiece in the phone. I was told that is why the ear piece is like a speaker coil and the voice piece is a carbon element that can be removed - but it is the earpiece that acts as the microphone in bugging mode. One time President Bush visited us on base. One of the phones made available to him was next to a secure crypto phone in our command post next door to our shop. I showed the president's technician the phone. He opened it up to make sure there were no bugging devices inside and then inserted a thin strip in the various contacts. He told me that was so it cannot be used as a bugging device. I told him about our box with the red light and he said it was similar to that. It was easier to temporarily modify the phones rather than schlep a bunch of "modified" phones with him around the world. This is one reason why telephones were leased (never sold) to people for so many years. It was the best way to insure virtually every room in the USA that had a phone was bugged. To this day, I disconnect my land line phone in my shop when I have private conversations there. Did you know this?

[@Hicken65]

The 3-slot pay phone didn't have any sophisticated electronics in it.You needed to put in a coin to get dial tone. The dropping of the coin physically operated a tiltable trigger which in turn closed a contact set that applied ground on the ring wire. So any method that would put ground on the ring wire would get you dial tone. The transmitter and receiver caps were glued onto the threads of the handset. Field repair technicians were instructed to replace the entire handset if there was a problem with the receiver or transmitter. It is highly unlikely banging the handset on a hard surface would have broken the glue seal. @@paulromsky9527

[@paulromsky9527]

@@Hicken65 They were glued on! That makes sense. Thanks.

[@viktordubowskii695]

In older cities, such as Philadelphia, there are still a large number of older people that still use there rotary phones.

[@Hicken65]

Apparently some telephone companies allow dial pulsing and others don't.

[@michaelbenardo5695]

I still use mine, and refuse to give it up.

[@wazza33racer]

Australian rotary dials never had letters............that was some silly American idea. We were dialling numbers, not names.

[@Hicken65]

This is simply not true. Large metropolitan areas in Australia had lettered dials up through the end of the 1950's. Each of the 10 numbers of the dial had one letter associated with it (which were A, B, F, J, L, M, U, W, X and Y). Subscribers would dial a 2-letter prefix followed by a 4-digit station number. I certainly wouldn't call Australians silly for doing this.

[@chrismc7205]

This harkens to the days when exchanges were named, and operated by humans. Americans got used to exchange names and continued for a long time.

[@Hicken65]

@@chrismc7205 The changes only began in 1960 because the numbering system had run out of usable 2-letter combinations that could form the start of a name. The change to All Number Calling (ANC) expanded the number capacity immensely without having to make any changes to switching equipment. The change was, however, not well received by the public and there was considerable pushback. But in the end , ANC prevailed.

[@wazza33racer]

@@Hicken65 I stand corrected..........however its strange that I have lived in a lot of old farmhouses, lived in country towns that were well and truly behind the times and never saw any old rotary phones with letters.

[@Hicken65]

@@wazza33racer I believe that in Australia, the letters were only used when a town needed more than one exchange. That is , when more than 10,000 numbers were required.

[@EJP]

Don’t dial with a pen buddy.

[@Hicken65]

Actually, it's a pencil with an eraser at the end to prevent scratching the number plate. There were a number of manufacturers that made dialing tools, which were quite popular with people doing a lot of dialing. The Bell System operators used pencils with a slip on tool (type KS8400) that had a round knob on its end and they also used mechanical pencils with the tool built in (KS8300). You can still see them on Ebay.