Building a Plain Old Telephone Service (POTS) Intercom

A discussion POTS phones and how to create an hotline/intercom using two of them.
Music used in this video (Vibe Tracks, Alternate) was downloaded from the KZbin Audio Library: kzbin.info_...
#retrophone

[@simonhanlon7518]

In the late 60's early 70's my Father figured out that you could chain all the local area codes together to phone anywhere in the country at a local call rate. That went really well until he told his friend at work how to do it.....which would have been fine had they not worked in top secret nuclear missile guidance system facility. His friend got a few numbers wrong and called East Germany....it didn't go down too well lol.

[@JohnsBasement]

🤣 I love it!!! 😂

[@bbqgiraffe3766]

Speedrunning a visit to a CIA blacksite

[@DL-kc8fc]

Relay switchboards were easily fooled. It was enough to turn zero on the round dial, and when the round dial was going backwards on the number 7, once again tighten the 0 to the end stop. If you did it quickly within the time limit, for example, 13 impulses were generated, i.e. more than would be possible by normal dialing, and you gained access to an intercity or interstate line. I used this method in an emergency and never told anyone. :)

[@secondhandsmoke10]

“Hallo :) ?” _”Shit…”_

[@MPW68]

😂🤣😂🤣 now that is wild

[@LandNfan]

In late ‘69 you could only get an answering machine from the phone company. So I built my own. Since ringing current is 90v @ 20 hz, you can rectify it to DC to pull in a relay, placing the device in an off-hook state. I used an old 4-track (remember those?) home recording deck for both the outgoing message and overall timing of the cycle. The tapes were the same as NAB broadcast cartridges, but they ran at 3 3/4 ips instead of 7 1/2. A 30 second broadcast cart ran for 60 seconds on my unit. I hand made a sense head from a small piece of hardwood with two bare wires wrapped around it. A foil strip in the tape would bridge the wires as it passed, tripping another relay to stop both the cartridge tape, the cassette recorder that captured incoming messages, and dropped the phone connection to go back on-hook. I think it used a total of four relays to manage all the “logic”. The most expensive part was a transformer for the power supply to operate all the relays. It had a lot of compromises, like the fixed cycle, having to listen to your outgoing message before each incoming, and not detecting if the calling party hung up and recording up to 30 seconds of dial tone. But it was a fun project and worked well despite its limitations.

[@JohnsBasement]

This is Awesome!!! Back in the day, I remember using the sleeve and ring of a 1/4" jack to trigger a foil-stop on a reel to reel deck. 😁

[@brickson98m]

That’s super cool. I grew up in the 2000’s, so everything was moving digital by then. But I still love old tech. So much more interesting and fun to mess around with.

[@Anonymous99997]

In the 70s, I built a simple intercom system in our high school auditorium from the lighting board to the spot light to the stage manager by wiring three hand sets this way. It was genius.

[@JohnsBasement]

I spent much time in the end of the 1970s in my high school's radio station and auditorium. The auditorium had bits of old telephone operator headsets laying around its closets from what must have been the same sort of thing. :-D

[@Coz255]

Back in the early 80’s, before cell phones took over. I took advantage of this very same working principle and designed and built an expandable home telephone switching system. The base system supported 4 extensions of touch tone phones, expandable in groups of 4, supporting a total of 16. It worked on touch tones, had it’s own dial tone and ringing system as well as one private internal line. I also wrote the programming to make it work. I still have the PC B's in my design archives….

[@JohnsBasement]

Coolness! 😀 Things USED to make sense until "no user serviceable parts inside" ruined things for hobbyists. 🤔 I wonder how much this continuing trend is stifling creativity?

[@Subgunman]

That is interesting! Any chance of sharing the info?

[@jtodd76]

This was very cool to watch. I'm 46 and when I was 7-12, I was so fascinated with phones and anything electrical and always went to DAV or thrift stores to buy junk and try to fix it. I remember hooking up a small speaker to the phone jack in my room to listen in on my sister's phone call. I also remember my mom telling me one day I'll have a phone attached to my ear!! She sure called that one back in the 80's and today, I own an IT business and always have an earpiece attached to my ear. Great video! Brought back some cool memories of tinkering.

[@JohnsBasement]

😂👍

[@THOMMGB]

I've still got a landline that's part of my DSL connection. I've got a Western Electric #302, built in 1946, hooked up to it. It's all original and still works wonderfully well. My metal-cased #302 is so heavy, you could drive nails with it! And when those brass bells ring, they're very distinctive, you know, you can't miss that a call is coming in for you.

[@JohnsBasement]

When Western Electric owned & serviced the equipment, it was cheaper to make it last. After the divesture, they started selling phones to consumers. Ya know, the kind that don't know the difference between "price" and "value." In order to compete with price against the likes of Cobra, they had to sacrifice 99% of the quality. 😩

[@ArchimGregorios]

My everyday living room phone is also a black Western Electric 302 with a metal body. It is all original and still works perfectly. It will outlast me. Since aĺ of the phones in my phone are antique rotary phones, I'm hoping that my phone company will still keep my copper-wire land lines in service.

[@the_internet_332]

Excellent, in working for three telecoms in the early 2000's I appreciate this video

[@ray_mck]

I clicked the video to learn how you were going to manage the ring AC voltage at 20Hz. I was disappointed when I thought you were going to only do an intercom system. But then I was ecstatic when you rang it at 60Hz. I've always just left my POTS equipment in storage because I thought that 20Hz was essential. It never occurred to me to just stick it on 60Hz! Thank you!

[@JohnsBasement]

Most welcome! Glad you liked it

[@kreuner11]

The phone system as we know it was around for way more than 100 years ago, since the Panel switch, the machine that connects phones together using rotating drums containing almost a computer program and columns of brushes moving up and down upon a Panel of contacts to find your line and a sort of electronic database to manage it all, was introduced in 1915

[@JohnsBasement]

It would have been amazing to be part of creating it!

[@frustro4323]

Always fun to share little projects with my friends. The design I came up with was a DC power brick,for a motor from junk cordless drill to drive a stepper motor from junk printer to make idle and ring voltage. We got our ring CPS from some switches touching cam lobes on the drive.

[@sebastian19745]

The line impedance of analog telephone was 600 (or 680?) ohm balanced. The voltage was 48V at some 50mA on-hook and dropped at 20V off-hook. The dial tone was at around 400 Hz. Ringing signal was at around 100V (60 to 120V) over the line voltage (so some 150V) 20Hz sine wave. Powering the phone was made though two inductances in series with the phone, one on each wire (instead the resistors you used) and the audio signal was tool directly from the phone terminals (line) through two capacitors, one on each wire. The audio band passed by the phone system was 300-3400 Hz, enough for a voice to be understood and recognized. That is what I remember (I think correctly) from my school time. There were also other standardized tones for busy, waiting and other signals that I do not remember. I remember those because I built myself a 4 lines automated phone commutation system for my house (3 internal and one external) and I did the circuits myself (relays commanded by a Spectrum computer with a custom ROM). Of course I used old electromagnetic telephones and at some point I changed one with an electronic one (with LEDs, yes) with pulse calling that also worked well. The system worked for 8 years until the computer died and I was unable to repair or replace it (I could not find another Spectrum computer at the time. However, the main communication at the time was by mobile so the old PABX was already obsolete.

[@JohnsBasement]

Cool! I wanted to build the one back in the day too. But school and $$ got in the way. I also switched majors from EE to Comp Sci around that time & lost my unlimited university lab access. 😕 Ran it with a spectrum? Why not!

[@sebastian19745]

@@JohnsBasement My formation is in telecommunications so all that is radio, telephone, TV, data communications is in my area. At the time I had telephony course and then I made my PABX. I used a Spectrum just as an Arduino today, made an extension board with relays as output and voltage level detectors as input. With a transformer from a tube radio I made the power supply for 48V and 100V and a oscillator for forming the signals. I used BD 139/140 as I had many of them at the time. The network was configured as 2x2 matrix with pulse code dialing and 4 numbers: 1-3 for the interior phones and 0 for accessing the exterior line. The computer I used just because I was lazy to implement all the logic and te ICs were quite expensive (not to speak of microcontrollers in late 90s), that is why I did not used DTMF decoders or fancy stuff. I programmed the computer and then dumped the RAM where the program was and burned in a EPROM that I put on the board. So there was an autoload in case of power failure. One can make the same today wit an Arduino and some relay and ADC shields. Making a program to control such a simple PABX should be easy: it consists in few loops. So why do not make one now? Even a simpler one with pulse dialing and no fancy stuff like DTMF, redial, line hold can be easily made. And as all is in program, can be fairly easy to add features. The specs of old telephone PBX with relays from 70s maybe can be found online if not on old manuals.

[@evillealbey1]

Thank you for this video. I've been searching for days trying to find the information you provided. You are very much appreciated.

[@JohnsBasement]

You are very welcome!

[@killaship]

This all is really interesting! It seems like it could be a fun project to cobble together a basic phone exchange that can understand DTMF tones, and then ring and connect phones. I guess I'll have to get my hands on a bunch of old phones and relays, first.

[@joshblades]

Really cool video John! I'm here in the UK and it was well known that the phone line always provided 12v, I've heard of people powering other devices other than phones before. Thanks for explaining how the ringer worked, really interesting stuff.

[@JohnsBasement]

Thanks. Analog phones are fun to tinker with.

[@johnathancorgan3994]

The internals of these are fascinating, too--there's a "hybrid" transformer circuit that connects the line to both the handset microphone and speaker. The hybrid sends the signal from the mic down the line and directs the signal from the line to the speaker, using the same two wires. Additionally, a small amount of the mic output is sent to the speaker ("sidetone") so you can hear yourself speaking even when the handset is completely covering your ear. Advanced tech for its time 100+ years ago.

[@JohnsBasement]

Yeah. That transformer was a bit of mystery to me back then. The original phone engineers were awesome! Have you ever read "The Idea Factory..." by Jon Gertner? Seriously cool place to be in its heyday!

[@johnathancorgan3994]

@@JohnsBasement Added to my reading list! I've met a few folks from Bell Labs over the decades, was definitely a fountain of cool stuff.

[@geirendre]

We had that exact same phone here in Norway. It was made in Norway, and called an "Elektrisk Bureau Modell 1967". There's a screw under the cradle where the handset rest that lets you open the phone up to show the inside of it. Used to work with those back in the day 🙂

[@JohnsBasement]

That phone has been around! 😀

[@EwanMarshall]

Yeah, it is not design the British ever used, doesn't match any GPO issued phone. I've edited this as my original identification of that was partially wrong.

[@joubertkristoffersen4183]

This is not a Norwegian model 67 from Elektrisk Bureu, but a Danish KTAS model that looks similar to the model 67. The Danish one is a conventional phone with an electromechanical bell, carbon mike and a magnetic earphone. The Norwegian one is very advanced for its day. It has electrodynamic mike and earpiece which are driven by a transistor circuit. The "ringing" is obtained by using the earpiece to produce a whistling sound, again driven by a transistor circuit.

[@g-r-a-e-m-e-]

Me and my brother had an intercom phone system in our house, in the 1960s. Still a fun project.

[@JohnsBasement]

So cool! And tough for modern kids to relate to the value of an intercom or a PBX.

[@Linkvagen]

It is a Swedish-developed phone called "Dialog". It was developed in the early 60s by Ericsson (LM Ericsson as the company was then called) and the Swedish Televerket (today Telia). The phone was also sold internationally and appeared in many countries.

[@JohnsBasement]

It appears you are right: en.m.wikipedia.org/wiki/Ericsson_Dialog .. I like the red one. 🤔

[@eliashki]

You had allready answered, sorry;)

[@henrywagner8042]

I'm in the younger generation and I am very interested in this! Sometimes I wish things could still be this way with the world more simple. I have 2 old phones and I'm planning on doing this!

[@JohnsBasement]

Things this simple should be something that everyone gives a try. You can even power an intercom system with a 9V battery!

[@mybluemars]

That was Fascinating! Thank You!

[@randallrouth9029]

Great video. You have all kinds of retro tech. Next thing you know, you will be explaining how 8-tracks work.

[@JohnsBasement]

8-tracks.. 🤣

[@randallrouth9029]

@@JohnsBasement a new channel, "John's Retro Basement". Explaining lava lamps, black lights, and how the raise a lower a car window by hand. Maybe include a multi part series on how distributors, points, and distributor caps work.

[@flinkiklug6666]

You gave me some nice ideas. Thanks for your video

[@JohnsBasement]

I'm glad to have helped! Analog phones were just cool. It is sad to see them disappearing.

[@flinkiklug6666]

@@JohnsBasement i am now building a old switching system for our house with 5 to 23 phones. To call someone who is on the other end

[@mrdavyjones]

I arrived in search of something completely different and, to my delight, found myself captivated until the very last moment. The content was so engaging that I couldn't help but hit like and subscribe to support and stay updated.

[@JohnsBasement]

Thank you for such kind words!

[@darylmorning]

I made a little intercom system for my daughters' early head start classroom in early 2000 with two $5 phones and a .9v

[@christopherrasmussen8718]

Grandad was a ham. We did this in the 70s. I bought a 20 year old motor coach 4 years ago. It has 3 Pots phones front to back and one in a box back by the engine. They had not worked in a while so I fixed them up

[@JohnsBasement]

Awesome! "Hello, engine room?" 🤣

[@fzbucks]

Thanks - had two phones that the kids have been playing with and wondered how easy it would be to get them to be able to talk to each other - looks pretty straight forward, shame the ringer would be too excessive to setup for them, they'll just have to keep shouting riiiiing riiiiiiinnnnnng like they do at the moment - thanks for the video

[@JohnsBasement]

You're welcome. Have fun!

[@alanmelb]

I worked on POTS telephone lines in the 70’s. Back then it stood for Plain ORDINARY Telephone Service. Today, POTS telephones are sadly much maligned, but POTS telephones provided an essential service during power outages. ‘Advances’ in modern technology have resulted in today’s digitally based landlines being regarded as 2nd class services, not to be relied upon and a good reason to hang onto that CB radio.

[@JohnsBasement]

Thanks for the corrections. Makes sense. I like my POTS phones! I had mine working up until a truck tore the lines & some siding off my house about 7 years ago. I decided to just cancel it and cut over to cell only service. It's not without its charms.

[@kenjewell5619]

If you have a 220R or similar resistor in the power supply positive, you can wire the phones in parallel, the speech path will work just fine.

[@allenquintana2868]

thank you! cool vid!

[@Subgunman]

Most European phones ring at 60volts 20 hz. Talk voltage ( also known as battery ) in the USA is around six volts while on hook voltage is around 48 volts. Ringing voltage was generated at the central office. Today these voltages are generated in interface boxes ( some networks call these DSLAM's ) where the voice is translated to digital data and sent to the central offices which routes the data stream of the call to the appropriate fiber cable to the correct interface box which converts the digital signal back to analog signals which are fed to the homes on copper lines. There are many municipalities now receiving fiber service to their homes.

[@hereforthefreewater]

Great video

[@JohnsBasement]

Thanks!

[@retrocomms]

Very informative!

[@JohnsBasement]

Glad it was helpful!

[@dalemettee1147]

You ca get a unit that gives a 20 Hz./ 90V current all from a 9V battery. It can be used for a stage effect.

[@pinu1166]

Hello, thank you for the wonderful videos in your channel, they are enjoyable and informative. I need some advice. I have two hand crank phones (western electric). They do not have any dials, the phone rings when the crank is rotated. Any idea, how can I connect these two phones to make an intercom? thought is if I rotate the crank in one phone the other phone should ring and by lifting the receiver I should be able to start the call. Do I need external battery or any exchange box? what type of wires needed. I am in Oregon USA. Thank you in advance.

[@JohnsBasement]

The hand-crank on those old phones is a magneto (same tech as the thing on a lawn-mower flywheel to generate the voltage for the spark plug.) If you simply connect the two phones together, they should both ring when you crank the handle. If you want to be able to talk to each other you SHOULD be able to connect the two together (like I did in my video) and put some bias on the line. I would NOT use a wall-powered system to generate the bias! The magneto can generate 100+ volts easily and could ruin a simple power supply unless you use some sort of protection on it. I'd use a 9V battery with a 200-500 ohm resistor in series with it. That should work, if not, add another battery in series to get 18v and try that. (The original system probably ran at 48v or more. The actual voltage is nominal.) Also take note that those phones typically have a spark-gap shut for lightening protection right on the front. It probably looks like a rusty penny cut in half in a staggered pattern. I do not recommend EVER toughing that thing if anyone is cranking either of the magnetos!

[@pinu1166]

@JohnsBasement Thank you for the reply. I had tried connecting the L1 to L1 and L2 to L2 and used a 3V supply in one of the phones, and it worked. I could make one phone ring by cranking the other phone and was able to talk thru the mic and receiver. One phone might have either a transmitter or the receiver problem.

[@EngineeringVignettes]

There is a neat story to the names of the 2 wires as well, "tip" and "ring". Still smacking my proverbial head against the virtual wall for throwing (or walking) away from a pair of Strouger switches I saved from my old college lab, when they tore the old central office setup out in favour of some PBX's. Doh. You gonna cobble together some slicks and maybe put Asterix on a Raspberry Pi? Cheers,

[@JohnsBasement]

I missed out when my highschool scrapped theirs!!! I wish I had a few of those things too!! Best use I saw was in the MIT Nickel Plate model railroad. About 30 years ago I got a tour of the whole thing from a really nice guy named John Purbrick. It was an incredible thing controlled by a PDP 11 (if I recall correctly) and it had a turn table that was positioned by use of a rotary phone dial and a Strowger. Google for MIT TMRC. (Yes I killed an hour doing just that. 😂) It looks like they moved out of building 20 since I saw it. I'm sure it is still incredibly cool!

[@beltonthree]

I am looking to take a POTS phone, and rigging up some recorded music/sound to play. I am wanting to put this in my basement bar setup, so people who were curious and picked up the phone, would hear the recorded message. Any ideas on the easiest way to set this up? I was trying to avoid having to hook up to the hook system in the phone, so likely the sound would continuously play.

[@JohnsBasement]

If you have an old analog phone I expect you can simply connect it to a speaker port in a radio. I expect you don't need it to be too loud. If that does not work you'll need to add some DC bias to the line as I did through a resistor or two. Then connect to a dpeaker port. An older stereo or radio should have RC coupling and therefore not care about the bias. A newer radio may not like it. You can put a 10uF cap (bugger voltage than your bias) in series with the speaker port on any stereo to be sure... Preferably non-polarized. Else put it in so that the bias positive voltage connects to the phone wite on the + side if the cap & the - side to the radio... With the - bias side to the other radio output wire. Eh?

[@rafaelantoniomarroquinosor1674]

Perfecta explicacion, me parecio muy genial (perdon por no escribir en ingles)

[@JohnsBasement]

Gracias

[@jselby88]

Hey John, you look and sound a lot like a John that I knew in Kansas City in the mid 80s!

[@JohnsBasement]

😂

[@marinvidovic763]

Man You just imagined nice Topic for entire SERIES of videos : "Let's build small telephone network for few local homes or within a farm property or local Kids huts ." This thing might get super interesting series for people to watch; learn and replicate. Thanks for sharing . Please EXPAND the topic.

[@JohnsBasement]

Funny you should say this... This video just popped to the most viewed in the history of my channel. You might not be the only one that feels this way.

[@JeffsTagtripp]

What me and a frend used to do back in the 80s is run the two phones on a 6v battery and have a hand crank from a bicykle dynamo next to each phone. If you whant to make the phone ring just crank the dynamo and both phones ring.

[@JohnsBasement]

Oh that's a great idea! 😂

[@YOURRACHINAPRIL]

So that's POTS!

[@OleJacobsen]

The ringing voltage is not "pulses" it's AC and it is passed through a CAPACITOR which blocks DC and passes AC to make the phone ring. In other words, the bell coils are not directly connected to the line they are connected in series with the capacitor (typically in the .5uF to 2uF range depending on phone model). This allows the AC and DC to "coexist" on the line. The bell circuit is indeed disconnected as soon as you lift the receiver.

[@JohnsBasement]

🤔 Makes sense. I suppose that makes it easier to detect a ring-trip.

[@OleJacobsen]

@@JohnsBasement It prevents and pulsing on the line (such as dialing from another phone connected to the same circuit) from making the bell ring.

[@Solja_J]

What size transformer for a 12 volt system? Like if you were going to power it with a marine battery ?

[@JohnsBasement]

Not following. If you use a battery, a transformer is not part of the circuit. If you DO use a battery capable of sourcing more than 500ma, then DEFINITELY include a series limiting resistor!! A tiny 9v battery will likely work fine to power an intercom.

[@joannasarcamedes8191]

so i had an old wall rotary dial phone. found the right kind of wire at a thrift store it connects to the little wall plug fine bbut doesnt connect to the back of the phone right. its too wide so what do i do now?

[@JohnsBasement]

Phones have all sorts of different jacks and cords. I couldn't say based on only this description. You can google for images of phones and connectors until you find the one on your phone, what it is called, and then google gor places to get one. I would just open the phone and see if I could directly connect a cord inside.

[@AvromCrovax]

Ok so if I have 120 volts ac to 9/12 volt dc wall plug box can I wire that in as a power supply?

[@JohnsBasement]

Yep. Pretty much anything from 9v to 48v will work to bias the line to make a POTS phone work. Make sure you have SOME sort of current limiting in there so your power supply doesn't fail if (when) the line is shorted.

[@mattparker9726]

John, this is cool, but I'm more interested in building a backbone system between multiple places. Can you do a video on that?

[@JohnsBasement]

😂... Sorry. I'm not up for producing a "This Old 4ESS" video in the near future.

[@janbill79]

So your saying how the ringer works? I kind of went right past me even though I was trying to catch how a ringer works, It gets a higher amount of voltage how much was it? And if my phone will only make a un healthy ring what IT needs more volts or the coils bad. or is there a capacitor that can go bad its only a 2009 single bell

[@JohnsBasement]

The proper ring voltage is a 48v, 20 HZ pulsing waveform modulated onto a 48v DC bias. But it should ring as I show on 24v, 60 HZ AC. If it buzzes or rings weakly then raise the voltage. Do not exceed 48. Keep in mind that it is going to buzz VERY loud into the handset if you keep the ring voltage on after you pick up the handset!!! I would not exceed 24V. If your phone won't ring then get a different phone.

[@telocho]

You will not short the 2 amp transformer connecting without resistor, since the bell in the phone has impedence, which is just like restistance, just for AC.

[@JohnsBasement]

I was more concerned that I could short it poking around with the wiring on the bench... or that someone else would copy it and....

[@TulgaD5]

Did I get it right that you only need 2 wires (or 2 pins) to hook up a phone? I always assumed it's 4 because the RJ11 has 4 pins. 2 for audio and 2 for the ring current. Also on a newer phone which has a ringtone coming from a speaker instead of a bell, is it also 90 Volts 20 Hz?

[@JohnsBasement]

Yep. All syms n 2 wires. All pots phones since day-1 run the same way! 👍

[@TulgaD5]

@@JohnsBasement Thanks for the fast response. Some wifi routers (which run on 12 V) also have a RJ11 port for telephones. Do they also make the phones ring with 90 volts ac? It's kinda hard to imagine for me that a little box like that, which runs on 12 V also can output 90 volts. Am I missing something?

[@JohnsBasement]

@@TulgaD5 A phone can ring at lower voltages as well. In my video I was ringing it at 24V. To be fully compliant, the ring voltage SHOULD be on the order of 90V. But 24 or 48 will likely do the trick on most phones. As for getting more than 12V out of a 12V power supply, note that the ring voltage can be run through a transformer to step it up. You can use a regular power supply transformer connected backwards... but be careful how you drive it. A transformer is an inductive load AND one designed for 50 or 60HZ is going to saturate if you run it at, say, 20HZ (that is why you can use a 50HZ transformer in a 60HZ application but not the other way around! -- it has to do how many lines of magnetic flux that can build up in the core before it becomes full/saturated. Bigger core = more lines = more time = lower frequency.) Therefore, ring your phone at a frequency at or higher than your transformer is rated and/or just let it saturate and provide current limiting at the primary so that you don't mess up your driver circuit. (Because a saturated transformer/coil looks like a direct short.)

[@robgrant3816]

Trying to do this with two old rotary phones but have no joy, all you can get is hearing yourself in the same handset but nothing goes to the other phone??

[@JohnsBasement]

You need a resistance in series with the battery. One way to do that is to put the battery in series with both phones in one big loop. (You must have the battery in parallel with both phones with no series resistance.)

[@Firealarmcollectorperson]

Hi, I’m wanting to set this up from my treehouse to the garage and was wondering if I could use a 9v battery and a 2k resistor? The only resistors I have are 2k and 820. Which should I use? (If any at all) Thanks!

[@JohnsBasement]

It'll work with no resistor. The 820 will allow the battery to last longer. But might be too quiet.

[@Firealarmcollectorperson]

@@JohnsBasement Thanks!

[@Firealarmcollectorperson]

@@JohnsBasement also worth mentioning, they are touch tone phones and I heard that without a resistor they can be damaged. Is this true? Thanks!

[@JohnsBasement]

@@Firealarmcollectorperson Not likely from a 9v battery. Phones are pretty resilient. Toss in 150-1000 ohms if you are concerned.

[@TrolleyMC]

While I agree that a hard wired intercom is a more secure communication than a plain modern phone call, I also hard disagree as wiretaps were extremely easy in the POTS days. If you really value security in communications, an end-to-end encrypted channel is way better than a POTS line.

[@Ice_Karma]

I've never had a problem with it, but I've been told repeatedly you shouldn't plug a 4P4C (e.g., RJ11) plug into an 8P8C (e.g., RJ45) socket, because it could mess up two of the pins.

[@JohnsBasement]

🤔 Now that you mention it... It *does* feel like the female-side is under a bit more pressure than usual. The plastic 'shoulders' on the 4-pin are probably pressing up pretty hard on some of the leaf-springs.

[@RealMesaMike]

The RJ-11 looks like really small ethernet cable connector? LOL. First time I saw an RJ-45 connector, I thought it looked like a large modular phone connector..

[@JohnsBasement]

Yeah... Me too. 😂

[@Pabloeskobar6680]

Good video , how in military or in civilians whas find a wire if whas cut or something else ?

[@JohnsBasement]

I'm sorry, I don't understand the question.

[@Mark3ABE]

The ‘phone isn’t British. The GPO never provided anything quite like that, although it is a bit like the 700 series. It is Continental - possibly, Danish. For intercom use, two standard telephones are usually connected in parallel with the power supplied through an inductor, or, as someone has mentioned below, a resistor of about 220 ohms. This means that the anti sidetone circuitry in each ‘phone will function correctly.

[@JohnsBasement]

Yeah. Sorry I misspoke. I should have done better research.

[@Reaktanzkreis]

The real abreviation for POTS is "Post Office Telephone Service" and this mean all sort of Phone lines , analog and ISDN.

[@JohnsBasement]

I'm thinking that probably depends on what country you are in?

[@winterradicallds8353]

Are those Europeanrotory phones work on 12 v and the American rotory are 10v? or dose it not matter

[@JohnsBasement]

See the comment from @sebaseu6832 lots of detail there. Analog hones pretty much work everywhere on 12-48v.

[@roamingcelt]

Think the added resistance is more of a current limiter?

[@JohnsBasement]

Not in the way you might think.. The resistance in series with the power lets the AC audio ride atop the DC bias (without being filtered by the power source.)

[@roamingcelt]

@@JohnsBasement In this circuit, we want to filter the audio from the dc and keep the dc from letting the magic smoke out. You can do it without the resistance, but at about +14v the phones sound overdriven. Also figured out the -48v, thanks to your video. If you run -48v through a flip-flop (easily done with MOSFET.) you'll get 90vac floating. And 20hz is low enough humans can't hear it. The next circuit is detecting off the hook.

[@RapperBC]

Well. I was trying to do this so I could test an old phone I'm repairing for a friend. Guess what I did? Connected the two phones in parallel. 😅 Oboy. Kinda embarrassing. Well, the damn thing works! (when connected in series) Hey man: thanks!

[@JohnsBasement]

It's great to hear when people benefit from these videos. Thanks!

[@GarryLoveless2]

And a rj-11 with a second line becomes a rj-14 🎉

[@brickson98m]

I would argue that a modern cellphone call is more secure than a hardwired intercom phone setup, unless you’re worried about the government listening in. A hardwired phone to your neighbor’s house can be literally wiretapped. The one ones who can “wiretap” a modern cellphone call is the carrier and the government, because modern cellphones use digital, encrypted signals. The only way to “wiretap” a modern VoLTE cellphone call as a bad actor, and not an authorized entity, is to use an exploit called ReVoLTE, which is very limited in real world practice. It also requires a few thousand dollars in equipment, and some good technical know-how. They must also know your phone number, and execute the first step of the exploit within 10 seconds of you making a phone call. And since they have to capture the downlink stream, they’re likely going to have to be closer to the tower you’re connected to than you. Not to mention there’s other hurdles to get over like finding the correct audio codec, transcoding, and compression of packet headers. Additionally, it all hinges on the base station (tower) having its LTE keystreams implemented incorrectly, allowing reuse of keystreams on calls made in quick succession. Pre-digital cellphones, a landline was far more secure. Now all this goes out the window if you’re a kid trying to talk to a friend without parents listening in, as many cell providers offer parental control that allow parents to receive an audio file copy of the phone call, and details of who you called, or who called you.

[@Thomas-yr9ln]

What people hate the most is beings able to slam down the receiver when angry.

[@JohnsBasement]

Indeed! Back when the telcos owned the phones, they made them like a tank! "Ah! You want to own one? Here is a flimsy piece of junk for 10X the cost!"

[@philcook9967]

You mentioned the polarity doesn't matter. Back in the 70's, my boss asked me to fix his phone so people couldn't call out on it. I installed a hidden switch that reversed the polarity of the red and green wires. When reversed, the phone worked normally, but you could not dial out with the polarity reversed.

[@JohnsBasement]

Very weird. 🤔 Pulse or tone? Neither should care about polarity. Or maybe ISDN? 🤣

[@coreycampbell1689]

@@JohnsBasement Probably a tone phone, the old Western Electric phones didn’t have a rectifier bridge so the tone pad didn’t work with reversed polarity

[@hopje01]

Not related, but ‘battery reversal’ is used in payphones to drop the coin. Other way to drop the coins is a high frequency on the line. 12kc or 15kc.

[@robertj4454]

Rotary dial phones will work with the polarity reversed. Early touch tone phones needed correct polarity to dial out. Western Electric, supply unit for the Bell System began installing a " polarity guard " in it's equipment so if the line (tip & ring) were reversed you could still dial out. After 1984 when anyone could make and sell telephone equipment the really cheap phones did not have the polarity guard and correct polarity was required. Line reversal did not effect incoming calls. I remember when some business locations would put a dial lock on their rotary dial phones so employees could not make long distance calls. However, people discovered that you could hit the switch hook buttons just right and dial out. Hitting the switch hook button sends out a " pulse " just like the dial does.

[@Xiantez]

The first time I found out that RJ11 works in an RJ45 jack... it blew my mind xD

[@JohnsBasement]

It is nice. But be careful. If you put a narrower jack into a wider hole, the outer leaf-springs are going to be pressured way into the jack housing. That could leave them weaker down the road.

[@BurkenProductions]

Looks like a regular Swedish Dialog or diavox phone

[@JohnsBasement]

You're probably right. I misspoke in the video.

[@adamjhuber]

2:42 not true. If you did not have a dailtone on the second pair (which you would only have IF you signed up for a second line) you would not have any voltage on the second pair.

[@JohnsBasement]

It was true at my parent's house in the 1970s. They had a single line and there was a Western Electric wall wart powering the second pair.

[@airix10]

I was like a girl I talked on the phone so much with my friends growing up, now the idea of sitting on a phone call with anyone just sounds like the worst thing 🤣

[@JohnsBasement]

😂

Not all old-style ringer phones will ring at a 60 Hz frequency, despite supplying the right AC voltage. But electronic phones will.

[@JohnsBasement]

This is a very good point!! They are designed for 20HZ. depending on the mechanical aspects of the phone it may not be an effective solution.

[@m.k.8158]

@@JohnsBasement If you put a single diode in series with the transformer, you will end up with 30 HZ which is more likely to work than 60 HZ. You MIGHT need a bit more voltage in some cases though.

[@JohnsBasement]

@@m.k.8158 🤔. 1/2 wave rectified 60 HZ is still 60 HZ.

[@m.k.8158]

@@JohnsBasement how do you figure that-if you chop off every other cycle, you will end up with 30 HZ-a single diode will do this.

[@JohnsBasement]

Diodes don't chop off 'cycles'.

[@yellowgruts8340]

It was actually "Public Office Telephone Service" before the telephone service got "old"

[@JohnsBasement]

I guess that makes sense.

[@PebblesChan]

Can you please hook up 2 modems? From 300 baud up to 57.6K

[@JohnsBasement]

I'll meet you half way.

[@sebastian19745]

It seems (I am not sure because I never did it) but if you connect the modems in series with a 24V or 12V DC power supply you can make them to communicate with each other and transmit/ receive data from one computer to another. Maybe with software control (?) because there is no dial tone, ring tone or other signals.

[@JohnsBasement]

@@sebastian19745 Yes indeed they will! Some direct-connect modems will probably talk to talk to another one without the DC current source. But not likely over too long of a distance.

[@sebastian19745]

@@JohnsBasement So yo gave me homework. Thanks, I have to try this. :)

[@activelow9297]

I don't miss the old analog phone system at all. Yeah phreaking was cool, but lets face it, I was about 50 years ahead of my time. I much prefer the modern ultranets and meganets.

[@JohnsBasement]

🤣. Yeah. I do NOT miss being forced to use payphones. Especially in a Chicago winter when on the road!

[@eliashki]

The phone is Swedish Ericsson Dialog

[@JohnsBasement]

Yeah... I misspoke. Sorry. 😕

[@eliashki]

We had the wall mounted model at Posti ja Lennätinlaitos network in lappland in finland when i was a child:) my grandmothers had exactly that model here in Helsinki

[@scrunchymacscruff1244]

4-Tracks, 8-tracks, 7 1/2 ips..it's all good

[@raxxbones9642]

You sound like Bryan Cranston

[@JohnsBasement]

😂.. Now all I need is to move my studio into an RV!

[@Earcandy73]

That phone is not a British GPO phone. It’s Swedish.

[@JohnsBasement]

Yeah ... I should have been better about googling it.

[@edgeeffect]

Doesn't look British to me. I'm , English, old and a bit of a phone fan.

[@JohnsBasement]

Yeah, I guess Ericsson is a Swedish company. But I've had folks tell me they have seen this model all over the world.

[@1977ajax]

FYI, not a British phone.

[@JohnsBasement]

Yeah.. my bad. 🙄 It should have been easy enough to look up.