Ask Hackaday: What To Do With A Home Intercom System?

[Kyle] just moved into a new home, a 1970s abode that was very modern for its time. When the house was built, a home intercom system was installed. Of course this intercom system was eventually disconnected, but now [Kyle] would like to find a use for it.

The intercom system is a wonderful piece of engineering from the late 60s and early 70s. The base station has an FM radio, a mono input (for plugging in a turntable, we suppose), and a huge speaker. The satellite units – one for each room in the house – are much simpler with just a push to talk switch and a volume control. Yes, in classic minimalist style, the engineers for this intercom system used the speaker as a microphone.

[Kyle] would like to keep the wonderful plastic fantastic aesthetic of the intercom system, but he’s looking for something cool to do with this hardware.  This could be the beginnings of a very cool, very strange house-wide artificial intelligence build, kind of like a consumer version of HAL 9000. We’re interested in hearing what you’d do with [Kyle]’s hardware, so leave your ideas in the comments.

103 thoughts on “Ask Hackaday: What To Do With A Home Intercom System?

      1. Yep, actually one of the best mics I ever had was a speaker I accidentally plugged into my mic jack on a recorder. I could hear my parents talking downstairs and on the other side of the house.

        1. Yup, the bigger the diaphragm the better the sensitivity is, and any speaker is mighty big compared to even a large diaphragm microphone. Downsides are rolled off frequency response and skewed directionality.

    1. Look up “dynamic microphone” on wikipedia. A dynamic microphone is like a speaker with the functions reversed — instead of applying current to coil to move the cone, sound waves vibrating the cone induce a current.

    2. A dynamic microphone and a speaker are essentially the same thing, as well as a motor and a generator are: they just reverse the same physical principle.
      To use a speaker as a microphone (most old toy walkie talkies did just that in the 60s/70s) you have to match its lower impedance and different frequency response; usually a small one bjt preamp/filter is enough. It works well, do not expect HiFi though.

    3. This is one of those things I love most about retro technology. In a world where we are spoiled with processing power, millions of special application ICs, etc… we forget the real magic of engineering that used to go into doing so much with so little.

      And it is really cool when you discover this anew or see someone else discover it for the first time.

    4. Sometimes they use a higher impedance speaker to improve preformance as a mic. When I designed telecommunications equipment, we used a 50 ohm (custom) speaker in talk-back paging systems.

      They also used dynamic microphones in “sound powered” telephones, they are still used on ships for emergency communications.

    5. Yes indeed. The US Navy uses (or used to, can’t see them changing it) a sound-powered phone. The ONLY difference between the mic and the speaker was that the mic had a push-to-talk button. The reason they have a button is that the mic is “open” (to the outside; headphones are pushed us against your head), so you aren’t putting noise (any unwanted sounds) into the circuit.

      If I remember correctly, they used a piezoelectric element to covert sound back and forth to electricity.

  1. See if you can wire it up to your landline phone, so that the push to talk button “accepts” the call but only for that particular room. Use a bit of text to speech to let you know the callers number as well.

    1. Wow! Tubes? That’s insane. Are we sure this was the 70s? We did have transistors in the 70s. I would be afraid to have tubes inside my walls.

      Makes this even cooler, though.

      1. ’70s were a transition time. Transistors were still ‘new’. IC’s were the rage. But tubes prevailed for lots of applications, especially those generated in earlier times. Sometimes there were ‘solid state tubes’, basically transistor re-creations of tubes that fit in tube sockets. Reduced power, but reducing plate power could effect the entire device since often plate heaters were wired in series (but not always).

        Learning to ‘think different’ was hard for many electronic engineers to transfer from tube to transistor technology, so for a number of years that co-existed in parallel universes

        1. Hard to imagine the Z80 and 6051, the forerunning 8-bit CPUs now taken over by Pentiums, etc were launced in late 70’s (in ‘home’ computers like the ZX80 and Acorn Atom then slightly later the BBC Micro. More interestingly, the NE555 timer, 8 pin IC was invented and commenced production in 1971 – and is still used today, in it’s same 8 pin DIL package.
          Tubes in the 70’s – I think it was out of date even in the 70’s tho’ some very high range audio amps continued using high spec tubes well into 21 century.

  2. How about setting up an Asterisk server and making each of the units an IP phone. The base station could be the server. There’s a Raspi distro for Asterisk so you could probably put a pi in each box (and probably power them all over the existing intercom wiring, which is usually fairly heavy gauge. Tons of variations on this are possible. You could probably hook up the “push to talk” switch to a GPIO pin or possibly a relay and use that to switch the speaker into a mic.

  3. On the front door station you could make it dial your cell when you aren’t home and use DTMF to control it. * to hang up and possibly another more complex code to unlock or open a garage door. just make sure you have a circuit that mutes the speaker when you issue DTMF commands so they can record them and use them later.

  4. Fill the satellietes with explosives, move the main unit to a panic room and get ready to remote detonate your entire house while safe behind inches of steel.
    Might come in handy one day.

  5. I love the look of this. I would probably replace the speaker with an LCD screen (and use smoked plastic to retain the black-out.) Connect a panning camera to the other end and control them with one of the knobs. Keep the intercom system (though replace with mics since the quality of using a speaker as a mic usually sucked.)
    Basically just a modern intercomm in a retro look.

    I also like the idea posted above about using voice commands. Basically an intercomm to the house intelligence. Unfortunately I rent a house, so I can’t make modifcations. But I have all the stuff to make “smart rooms” where it senses where people are in the house and triggers things.

    When I was a kid, I dreamt up a system using my commodore 64 to answer the phone, ask the caller who they were and who they were looking for. Then it would check the rooms for people and negotiate whether to take the call or not.

    It’s amazing how complex of a system that required back then, but with todays technology, it is relatively simple in comparison.

    1. How are you doing the person tracking around the house. I’ve been thinking of a little project which could really use this tech. Is it a passive or active system for the user, ie, do they need to scan an RFID tag on entering a room, or have you come up with some kind of clever image tracking? I had considered using a passive RFID tag put on a key fob for example, the reader would then be triggered by IR when you walk into a room. But that kinda means you have to carry a tag everywhere with you.

      Mobile phones would be another option but again I’d still be using NFC, I did also consider a system of motion detectors around the house that could be used to track people, but I never really fully fleshed that idea out.

      1. We are talking Commodore 64 era, here. Late 80’s early 90s. No RFID. My plan was simply motion detectors and voice prompts in the room asking who was present when it found someone. Implantable RFID or RFID jewelry would probably be the way to go now. Some smartness, might even be able to determine what room you have headed to based on the path. Which would help when RFID gets out of range.

  6. the speakers probably are way to sucky for music distribution, so that isn’t interesting. Keep it as an Intercom, but as someone above suggested, make it VoIP enabled, then you can always add home control systems etc. easily
    Speaking to someone at the door from everywhere would be nice, too.

    1. The idea was to tune in your fav radio station and have it playing as you worked throughout the house during the day. My wife pauses the TiVo while running tom the laundry room, would be nice to have TV or music piped in there…I do have a tap of the TV audiom out running to a guitar amp in my basement workshop so I can listen to TV while working. It would be cool to have a old intercom system, I’d just use the existing aux channel. Future upgrades (IR remote, DTMF or whatwever) could be added as needed.

      The only time we needed a true intercom was when I installed one between the house and my dads workshop. Used the second pair on a phone line so mom could call dad to dinner.

      1. Almost exactly the project I’m in the planning stages of. The key idea is tracking people throughout the house so instead of piping the same thing through the house each person has their own stream which follows them and pauses one stream if the person passes into an area with another person who is listening to a different stream.

        It’ll have a few toher features too, I’ll just have to impliment them while I think about the tracking.

  7. Hang on a minute – you mean no one has yet suggested to use the in-wall-wiring?

    No one has yet suggested you attempt to set up a secure in-house internet?

    1. 10BaseT cable uses twisted pair cable. So does telephony. The big difference is there are more twists in the pair as you go up in frequency.

    2. Chances are, what ever cable connects these wall-boxes, some if not all are twisted pairs to reduce the hum from the mains.

    3. (I think) You don’t need all the wires in a 10BaseT cable. A 10BaseT cable is wired for full duplex. But (I think) normal installs only use half duplex or some of the pairs. So you might be able to get away with just a few twisted pairs.

    Even if you can’t pass 10BaseT signals, this is a great chance to use other protocols over these cables. I think there are several house-automation protocols that don’t require much bandwidth.

    The real “gold” here isn’t the wall units, it’s the cables buried in the walls.

    1. Having helped replace a few of these, I can say for certain that none of it is UTP cable. Most of the wires are 10ga solid core copper, and a few are 8ga.

      Also, at the time this house was built, most home telephone telephone wire wasn’t twisted pair either.

        1. True. I remember that…. not that many people cared for the phone company’s restriction. People always kept the company’s phone in case they had to call a tech to troubleshoot something ;D

      1. It’s got to be worth trying – Don’t forget that the network only uses two twisted pairs (4 wires) and twisted pair means just one twist – Modern ethernet cables actually do not have any twist – the geometry of the cable/sockets gives it the single twist it needs. It’ll lack shielding, and the copper will probably have voids etc., which won’t help, but it might work tolerably well in practice for IP radio and video intercom (“Sorry – I had no idea you were naked, fnarr, fnarr.”).

        If it doesn’t, just put it all back and put in some mood lighting – Another thing that became popular back in the ’60s and ’70s when “pigs in spaaace” intercoms and all-pervasive muzac were imagined to be symbols of la dolce vita, and is still as excruciatingly naff today as it was then (“Have some Madeira, M’dear”). Even (particularly?) when done with LEDs and arduinos.

        As someone who lived through the 60s, my suggestion would be to make it completely authentic – Throw it in the landfill so it can join all its misbegotten siblings. Most 60s kit is grossly overrated.

        1. Are you SURE about twisted pair? The twist is supposed to reduce interference and crosstalk. Every bit of twisted-pair I’ve seen has been… twisted. That’s why it’s called twisted! The crossed-over pins thing is a separate issue.

    2. While (as the others have pointed out) you wouldn’t be able to run internet over the existing wires, you might be able to use them to pull new wires… (depending on whether the existing wires are stapled down…)

  8. raspi + lcd + base station = 3d etcha sketch? wierd game console?

    rc aircraft contoller?
    You could make a big quadrotor (bonus points for using the satellite units as trancievers)
    Add a controllable camera. A Raspi in both the base station and the quaddy could be taught simple AI tricks for a little “auto pilot” or “assissted pilot”ing if you will. A screen could act as a monitor. There are ample swiches to switch modes and give commands quickly (switching on and off camera recording , switching from video to snapshot mode etc.

    if you dont like flying gizmos, you could as well try an RC robot / car/ tank/ etc.

    1. Best Idea Yet!
      you could turn the copter/car/tank into an automated beer delivery system (the heli would be the coolest, if it can carry a full beer) then you could also have it drop your empties into the recycle bin

  9. Find some entity to sponsor an IoT contest to do the most with the least (think Arduino), between yours and the MILLIONS of other homes out there that have these systems installed. They were very common in my day, and known for failing (think Lighting).

  10. Re-engineer the ‘innards’. Make RFID or bluetooth tags for residents, and have the units detect who is where, and map them on a LED screen on the ‘base station’ and make it available on tablets/phones. (even tags for keys, so lost keys could be found).

    Drive your stereo, and have the sound follow the user, with higher priority user can override residents by just waling into the room.

    Put a Sari clone on the unit, and allow a computer interface for all residents throughout the house. (Shades of old StarTrek episodes).

    Install ‘portable chargers’ around the house for robots/iRobot Rumba clones to use and know where they are. Allow direction to the next rooms to be used. Or use robots like the for similar manner.

    Put camera’s in each device, similar to Kubrick’s 2001 HAL computer stations, with a computer like RaspberryPi in each station.

    Where these devices aren’t already, make a ‘portable radio’ like device that interfaces via WIFI or similar, and have camera, keypad/switches, display, speakers etc available on this new ‘remote device’. Make it water safe to use outside, near pool or sauna, (put it in a sealed mineral oil bathe?), but Boze Wave Radio like sound system. Optional install of 3D cameras, Imax resolution?, stereo or better microphones, all made available for a ‘yet to be written’ telepresence or virtual presence (think 3D HAL or SARI type) application.

    1. Time for ‘Trek comm badges to come to life. Even the old ‘talk to the computer’ was done in the old Treks via a ‘ship wide’ room-intercom type device. … Oh how life has changed. Now days, we text our appliances (or get texts from them) across the room or world just as easily.

  11. The awesome retro tech look means the most obvious, HAL 9000 implementation, is truly the best choice. If the system were hooked into a central controller and the network, and used iSpeech etc. to do some home control or, basically, anything, and talk back, it would be the most excellent functional art installation EVER.

      1. Why does that make him worth his salt. Not that I would have expected an installer to think of this in the 70s but pull able wires are so much better when upgrades are available every few years. I would love to pull some of the coax in my house to run new Ethernet! It’s not like an unstapled wire would go anywhere of it’s own accord,

        1. Yeah, it’s the contrary. Stapled/glued/nailed things are THE sign of poor workmanship on anything.

          Well assembled things are always, as far as the physical requirements will allow, assembled with mechanisms that can be undone without leaving any damage on the materials they hold together.

  12. When I was a little kids we had one of those in our house. The thing that I remeber about ti was that you could only call out from the main unit. If I remeber ours was brown or copper in color but that was a VERY LONG TIME AGO.
    If you could pull CAT 5 or 6 to all the location you could add video and other iteresting stuff to it. Just adding a computer to the base station you oculd do some interesting stuff like voice control and routing so you could call one bedroom from another.

  13. I moved into a house that was made in ’77. It has a 8 or 10 room nutone intercom system. Theres a rat’s nest behind the intercom of all the 6-conductor wires coming from each room.. It no longer is working properly though. Popping noises and buzzing. I suspect a wire shorting.

    In the first few years that it was working, I had removed the mono RCA wire running from upstairs to downstairs. wired to an 8 track player, baby.

    Then I hacked it for use with an airport express, ran the line out into a 470ohm attenuator, combined the signal into the mono rca input on the back of the intercom panel. Worked great, even used other airplay devices simultaneously in itunes. Named it “Nutone” in iTunes. it was like it had airplay built in.

    1. hi Jared,
      I just moved to a new (old) house with an intercom system. I am not a tinkerer but I am willing to give it a try & “upgrade” my old system with Airplay.
      Could you give me more details on how you did it?


  14. Is there a way to use it as a security system? Maybe you can call it (with Skype?) and hear what’s happening in the house. Combine all of the rooms into one audio stream or dial each room separately? Have it call your cell phone automatically if a sound is made over a certain decibel level? Add motion activated cameras for video calls too?

  15. I say use it for home automation, except…
    in each room put what ever ardunio or other home automation system you need.
    have the central base station push an intercom button (with a motorized finger) to open a channel into one room. then allow a really old modem to squeek and squak through the intercom to communicate with a similar system in that room. so basically each room would have an old modem used for audio communication, and more advanced systems for actual automation..
    it works great unless you’re anywhere in you house while the base system makes the rounds and calls each room in for status. ;-D

  16. Unless you want to pull new mains wiring in the walls, you’ll could certainly reuse the existing wire to carry electrical power to these devices. Consider that 22 AWG wire can have a somewhat significant voltage drop on a low voltage line due to resistance. You might want to keep the original 16VAC bell transformer in the circuit and drop the voltage the rest of the way at each device.

    As others have pointed out, the current wiring won’t be nearly reliable enough for ethernet traffic, but it would work just fine for RS 485. Of course if you need bandwidth to carry video or audio, you’ll probably just go wireless anyway. But if you just want to transfer small data packets (home automation sized) you could carry them quite easily over a serial link.

  17. Repair/restore to use in it’s intended function. Perhaps ad an input to play digital files. Not that I’m a fan of whole house music. Sorry I don’t get all the praise heaped on this old unit. Just a simple radio receiver with extra circuitry for the intercom. Nothing special in the engineering. As engineers do today they look at what is available to create what they are asked to create. Using the space saving devices of their day multiple capacitors in one can, resistor networks(often product specific) dual triode or pentode tubes.

    1. It’s not about “praise” so much as what this unit represented 40 years ago. It was instant person-to-person communications like they had in Star Trek, apart from you had to go over to the wall and push a button, then broadcast to everyone in the home that you wanted Tommy to come take the trash out. It was whole house music, just like they had in Tomorrowland at Disney World, except it played FM broadcast music. And it was all wrapped in this plastic and brushed chrome frame set flush in the wall, and not just a beige box hanging from the wall like the telephones of the day were.

      In the 1970s, these units were the next step towards “the future”. Sure, they were limited and cheesy, but it was a step.

  18. pumping station one has a cool system setup to monitor activity in each room. its just a webcam system and some custom software, add that to any of the above ideas for added awesome.

  19. USB controlled audio smartphone dock.

    Add a raspi or a sone such board. Replace the speaker with a good subwoofer. Write custom software on both raspi and the phone which makes the base station’s knobs and switches controll the software and audio . The audio could have multiple outputs- speakers, fm, etc. all controllabe thrpugh the switches. Also, the base station knpbs/switches must be able to swicth programs on the smartphone- movie player, songs, audio streamer, etc. Some other knobs could control the chamnel/playlist/etc.

  20. Here’s what I did at my first job — for a sound man who installed & serviced those:
    *** !!!!Danger! HVDC, 200+ VDC, and AC line voltage inside main chassis!!!!!
    * Filaments glowing? Good! They may be all wired in series, a circuit direct connected to the AC line! — DANGER!
    * First numbers on tube type is filament voltage, will add up to 120 (volts) if you have series filaments. e.g 35W4 was a 35 volt filament rectifier tube. eBay for “RCA Tube Manual” for ++info
    * Check for B+ (if you don’t know it, don’t do it!!)
    * If you get hum, replace power supply filter caps
    * Google or eBay search for schematics (“Howard W Sams” published schematics for everything made in the tube days)
    * Signal trace / signal inject the audio stages [grids only], output stage first working backwards:
    o Replace cathode bypass cap on output stage
    o Check no DC gets through coupling caps to control grids of next stage
    * Radio stages might be fine, if not… I’d replace with solid state
    * Get some cleaner spray for the pots if they’re noisy
    * Have it on an isolation xformer when open!

  21. I’d go with a touch screen LCD to replace the speaker – put a new speaker in the bottom vent.
    Then put a camera and mic in the radio portion on the right. Replace the switches with buttons, and the pots with rotary encoders with buttons for some input.

    Then you can program any home automation / media stuff you like. -RasPi would be good for this I think.

  22. My grandparent’s house had a similar thing so my grandma in the kitchen could call my grandpa in the basement yet it wasn’t difficult to simply yell down the stairs! My current 1920s house has the remains of a possible old crude telecom or buzzer system, with buttons built into the stair railing upstairs and downstairs and a few feet of wiring still there. I plan to do something with it so it’s easier for people to reach each other considering we have two family members with hearing loss.

  23. 1) something simillar was in a famous Tarantino movie, i forget the name. the one with the glowing “boss’s suitcase”

    2) really vaccum tubes? replace ALL the electrolyttics ***_BEFORE_*** “just trying it”
    … that will prevent the destruction of your precious vinatge tubes. 2$ of new caps and 50 cents of solder -OR- 200$ of damage to the tubes, take your pick. Plus shorted caps connected to tubes means it might catch fire WHEN tubes melt down. may also burn the output transformer and resistors. CAPS ALWAYS FAIL WHEN SITTING IDLE FOR 50 YEARS. half the time they failed shorted == tube meltdown. caps are cheap. you have been warned!!!!!!!

    3) i had a 600ohm telephone speaker that when i removed the line dropper resistor (zenerdiode?) that was piggybacked onto the speaker, it became a SUPER-DUPER sensitive microphone. it picked up whispering all the way downstairs, just like one other poster referred to. just had to connect it to a microphone-in (actually, tape-head preamp, but same signal voltage). it was creepely sensitive and im sure was the perfect fit for anyone trying to do paranormal “research” stuff

    PS: although the schematics for tube stuff usually have a fuse, you will find that the actual hardware often lacks any fuses. fuse-resistors werent invented yet. oh and forget line cord polarity.

    PS the (inside) metal frame might be live!!! plastic volume knob fell off? DONT TOUCH WITH WET HANDS! gooooogle

  24. [Kyle] and [NewCommentor1283] and [Iwatcdr]:

    * [NewCommentor1283] you are *so* right-on with all this. I haven’t worked with tubes for 35 years, and the “[power-]transformerless” design of that era was just crap. Not in the same class as a beautiful Fender tube guitar amp or a Fisher 500-C hi-fi at all. All of it was downright DANGEROUS, easily LETHAL inside, but “[power-]transformerless” stuff was moreso. Sooooo much safer to debug modern day hardware and software. [Kyle], do the right thing and RasPi / Arduino / whatnot it, but modernize it to today’s safer and sexier tech. I really like the ideas proposed, particularly substuting a darkened screen for the speaker, with a substitute speaker using the vents needed to let out all the heat from the vacuum tubes.

    * The Nutone unit, if perfectly restored, would only put out a watt or two of audio output power, burn a good 50 to 100 watts of AC power 24×7 (it doesn’t have an on-off switch, does it!), give off a “hot glass and dust and wax and varnish (and maybe selenium rectifier)” smell, and there will always be some 60 cycle hum on the audio because the filaments are on AC and the power supply rectifier is half-wave — cheap, cheap, cheap because it *had* to be. They worked, but not anywhere near as well as today’s tech works. And it’ll gradually lose what performance it has as the tubes degrade. [NewCommentor1283], are they really worth hundreds? A few bucks each back in the day, but that was then. Sounds like you’ve been bit by B+ once or twice.

    * Bogen was another name from that era in intercoms.

    * IIRC, the vacuum tube Nutone intercoms had a small, gray, metal-shielded, cylindrical input transformer. No label, it was a Nutone-special part. It was a step-up transformer which:

    (1) Matched the low impedance of the speaker-as-microphone (units of ohms) to the first audio gain stage’s input impedance (10^5 ohms, vacuum tubes were great that way). Turns ratio could have been, I suppose, as good as sqrt( 10^5 / 10^0 ) = 300:1.

    (2) In doing that, provided a “listen mode” signal voltage step-up, thus making fewer stages of voltage gain necessary. If that signal input (“listen mode”) xformer was a 1:300 turns ratio (don’t know for sure, again, just guessing), then it gave a voltage step up from microvolt level (right at “tape-head” level, as [NewCommentor1283], you’ve observed) to fractions-of-millivolts. Whether that was enough to go directly into the signal chain at the “AM detector” / “FM discriminator” stage, or did it need one extra gain stage before that, I don’t recall.

    (3) With its ability to withstand AC line voltage and more, isolated the station wiring and stations from (as [NewCommentor1283], you’ve well noted!) the possibly direct-to-one-pole-of-the-AC-line internal chassis. “Ground fault” voltage and current could have put the hot side of the AC line all over the house otherwise!!! Good God I disliked troubleshooting *those* “[power-] transformerless” vacuum tube units, intercom or TV or whatever else it was (TVs were the worst!!! Half-wave voltage tripler rectifier right off the AC line, hot chassis, YUK!). B+ was lethal enough, now we might have the ‘hot’ side of the the AC line (talk about low supply impedance!) all over the internal “ground” if AC plug polarity was not properly observed, or an isolation transformer was not used when debugging!!!! There’s a reason one blade of the AC plug was wider than the other, it was to put the AC line’s neutral on the internal chassis side (which *still* isn’t safe to touch; turn it off and *everything* rises to hot-side AC line voltage, including the internal chassis!!!). No “power transformer” to add weight and take up room, but good lord, one side of the AC line was on the internal chassis. Yeah, that’s bad folks. So you like vacuum tubes eh? You don’t want to mess with “transformerless” tube circuits, they were crap because of the lack of AC line isolation; it was just a cheap trick way of making them work for less expense. Sure you’ll get that “hot glass and dust” smell but you might get killed before you get there if you DIY this. Send it to a shop if you want it to work again as-old….

    * So [Kyle], if you choose to rebuild it with new tech, keep or sell the tubes and that input transformer, and keep the radio dial string and spring and pulley and cord intact. After removing all the parts except the tuning capacitor from the chassis (you’ll need to drill out the rivets holding the tube sockets in place) you will have lots of room, and a good metal structure with holes in it where the tube sockets were, all upon which to support a lot of new tech.

    * [Kyle], you *could* rig a real replacement AM/FM tuner to the “slide rule” radio dial (yes indeed, that’s what they called them in those days, and the vertical dial of the Nutone intercom was AFAIK a rare if not unique visual design, and yes it was thought ‘sexy tech’ to have a “slide rule” radio dial). You can re-string those with waxed cotton wire-wrapping cord (if that’s stil sold). Find any solid state AM/FM radio with a knob (not buttons) for tuning, and it *will* internally have a 180-degree rotation variable capacitor somewhere, with geometrically the same rotation as the Nutone’s tuning variable cap. There will be a big plastic pulley on the tuning cap; keep that pulley! Rig some kind of mechanical connection from that pulley (maybe stripping the plates out of the orig cap and gearing to its intact shaft?) to the tuning cap of the replacement radio’s tuning cap. What a hack that would be! A “Tecsun BCL-2000” radio has a variable cap tuner, but it’s too big for the Nutone box. You’ll have to look around for something that’ll fit but not take away all the room for your RasPi / Arduino / whatnot. Or rig a rotary encoder scavenged from a printer (they have especially fine rotary and/or linear quadrature encoders) and use software to command the push buttons of a hacked digital AM/FM radio. You’ll need to do a calculation in software to convert direction and number of counts from the encoder to button-pushes to get the Nutone’s dial to correspond with your replacement tuner’s tuning steps. A nice challenge.

    * I do like the idea of keeping the “paging plus talkback plus radio with talkback” ability intact, but with updated tech to allow other functions of your choice. As has been suggested, get Siri to listen from any station in the house, get your software to recognize the verbal command “COMPUTER!” as a button push, and there you are: Starship Enterprise, home version.

    * I haven’t worked tubes in 35+ years and was SO glad those days were coming to an end in the early 70s. Working a few summers for a Nutone installer I got bit by high voltage (“B+”) too many times, any one of which could have been my last, no kidding. Still I preferred bench work to crawling around in other people’s attics stringing that 4-conductor flat brown wire in one hand whilst carrying a hot 100 Watt trouble light in the other. No cool fluorescent or LED trouble lights in those days.
    (Ah, memories. Thanks [Iwatcdr] ).

    * Gotta’ give Nutone credit for knowing their business.

  25. [Kyle], just looked closer at your pix. Notes:

    * Since it’s complete and apparently undamaged (but for likely component degradations well-noted above), you might consider, for preservation’s sake, selling the subchassis as a whole, but keeping the cabinetry and clever shelving, wherein: (1) The full chassis pulls out from the “rough-in” frame (which frame you have removed from your wall). Pulling away the main chassis involuntarily and immediately disconnects the chassis from the AC power socket in the frame, rendering the chassis safe for service after a while [that’s the “interlock” feature] (2) The low-level remote station wiring is in its own fully shielded wiring box, with the remote station switches staying in the frame. Shielding keeps the low-level safely wiring away from AC line wiring, and keeps its microvolt-level talkback signals from hum pickup, and allows easy station wiring (don’t have to have the main chassis in place).

    * You could make your own overlays for you new front-panel legends, fitting them over the original areas. Photoshop the lettering to keep the old style.

    * Cleanup of the internal dust is easy: With a vacuum hose nearby, use a 1″ flat paintbrush to loosen the dust, letting the vacuum hose take it away. Like new when done.

    * There should be a model # and a tube layout sticker somewhere. Would be nice to see a pics of that. (That knowledge will also help you sell the subchassis, if you decide to do that).

    * Would also be nice to see close-ups of the lettering on all the controls.

    * Yours is a 3-wire system (paging & radio on one, common ground on another, low-level talkback on the third — simple). Some were 3 wire, some 4-wire.

    * I see the chassis, except for the FM RF/tuner section, is done in the the “last gasp of the tube era” style of tube sockets soldered directly to a (cheap, oops, minimalist) “paper-phenolic” brown PC board (not the better quality epoxy-green fiberglass boards we all use now). That “paper-phenolic” kind of PC board could crack or break easily, breaking the copper traces (don’t ask). Or the heat from the tubes could cause the traces to lift and break. But your board looks quite good; no discoloration visible.

    * There’s Nutone’s input / isolation / impedance matching input transformer, over on the right. 4 wires, primary and secondary each as separate twisted pairs coming out of the top of its cylindrical (shielded) can.

    * The inner ‘chassis’ (mostly that PC board, it turns out; no drilling after all) is indeed connected directly to one pole of the AC line. The red letter warning says so, where it reads “(Part of chassis is connected to line)”. It wasn’t red for nothing. Another proof: Note the black cardboard piece on the FM tuner section (left side), in good-looking condition. The whole ‘inner chassis’ is insulated using cardboard like that; there’s probably a piece under the PC board. It all had to go back in upon reassembly after servicing. Ignore a piece of cardboard and the customer’s front panel would be connected to one side of the AC line. Of course the electrician doing the AC power wiring would be given a clear indication of which pole was to go to neutral, and in those days, few mistakes were made. But of course the neutral pole isn’t safe to expose (ask any electrician); should the downstream neutral wire to the house’s service panel go open anywhere, (1) nothing upstream will work because there is no return path, and (2) all ‘neutrals’ upstream will float up to the hot side voltage!! So while acting ‘dead’, the open neutral, and any exposed metal connected to it, becomes deadly. Now you know why there’s a separate ‘Ground’ wire in all AC wiring — to give that potential somewhere safe to go. 7th grade Electric Shop knowledge in 1970. Today, not so much.

    * Once the inner chassis is out, you could remove the glass plate having the radio section’s vertical “slide rule” scale, replacing that with an LCD display, keeping the big speaker — or not.

    * Instead of applying this to home / intercom applications, you could build a tabletop cabinet for it and make your new functionality wireless.

    Apologies for going on and on, but I’ve serviced those very units. You’ve brought back a flood of memories. Thank you [Kyle].

    Choices, choices. Yours to do with as you wish, but be safe.

  26. So home theater system anyone, combined with the home automation kick…
    Yeah i remember the days of using headphones as microphones matter of fact in some instances alot of people still do when they are short of a mic or just low on cash.

    Simple solutions solve complex problems.

  27. Don’t know about the intercom / p/a / monitoring options on the older system, but mine from the early 80s had a set of switches in the main console that configured, for each room, whether it was normal (PTT from the room, p/a and music from console), off, speaker only, or monitor (live mic only always on). I used it occasionally as a baby monitor, configuring the baby’s room for live mic and turning off rooms from which I didn’t want to hear it while leaving the rest on. The annoyance was that configuration could only be done from the console. So… using the standard buttons, add a means to reconfigure the system from any room, perhaps with audible menu/confirmation. Since there are only a few buttons, use them like an old pulse phone—push 8 times quickly for an “8”, etc. Mine also had the AUX input on the console, to which I patched the “Digital Cable Radio” box, but would now attach internet radio. Add the means to “tune” that from any room. You can get to mid-fi audio by adding a small amp with high impedance input level and better speaker in each room (separate the speaker/mic functions). Afraid the wiring might be stapled, as others have said. Adding any other features is probably most easily done via wi-fi, unless something like RS-485 suffices, and even then it might not work well to all rooms. That said, some of the cheapest (~$30) analog video cameras will send a crappy signal down a hundred feet of flat cable, so that might work.

  28. * Remove the entire original guts as a whole, keeping that complete.
    * Put a color display where the radio tuning rectangle was. With that display, emulate its “slide rule dial” as an audio channel selector (of internet-sourced music / your music collection / an actual digital AM/FM tuner ) by:
    _____o Taking a good quality image of the original dial glass so you can photoshop the design for its channel separator iconography and its type face
    _____o Put a rotary encoder on the Tuning knob
    _____o Use the rotary encoder as a one-dimensional mouse cursor (up and down only) on the screen to do “channel selection”.
    _____o If you hack in a digital AM/FM tuner, emulate the original display as one of the “apps” your software will run.

    1. That’s a pretty sweet idea from 6L6GTB. What about picking up some used iPod Touches? They might fit into that space? With network access from each intercom, and the right app, could have a nice coordinated music player system, home automation, etc. (the rest of the legacy panel is just for visual effect).

  29. Turn it into a pandora box. Use a lcd display cleverly hidden in the tuner window to show the stations and make the knobs 1, play/pause, 2. station change, 3. volume, and 4 on and off

  30. I have the exact same one! I repaired it so it functions as if it were brand new. Still quite scratchy radio, but super cool! I would suggest when you are doing any of the above projects; add an amber light in the housing to cast the “vintage tube glow” on the wall. Subtle, but I think that would be cool. Try and make it slowly get brighter over a minute or so, to replicate what it originally would do.

  31. I am SOOO glad I found this site. I found a ton of places that want me to upgrade to something new for a few thousand bucks. No way! I have that exact unit and all speakers but the front and back door work now that I cleaned the pots. BAD hum and hard to get a good radio signal (especially over the hum. I LOVE the look of this thing.

    My thought is:

    1. Use the FM/AM area and make a “holder” for one of our old Android phones and run a headphone jack and power somehow in there for it. A little shelf and some kind of hi-density foam or car bracket contraption to keep it in place. It would double as a clock/mini browser too. May even consider getting a Virgin Mobile monthly plan and having it as a “home phone” and not even bother with wifi.

    2. Pull the power side as stated above and sell it off and replace with something like this – digital audio power amp and feed that powered line into the system.

    3. Replace the knobs and pots as needed and not touch a thing else.

    Will this work? I would be out about $50 max and have a great digital info station near my kitchen that would pump music through the house and still give me the ability to use the intercom to wake the kids to something loud and obnoxious every morning or have music outside this summer, etc.


    1. Hum likely due to a sour 2-in-1 or 3-in-1 electrolytic filter capacitor in the power supply section. Waxy paper thing with 3 or 4 wires and so many uFDs per section, color coded wires. 10 to 40 uFd maybe? Look for it, find a replacement with same or higher WVDC (working Volts DC) per section (don’t be surprised to read 400 WVDC, tubes work on high voltages).

  32. hello – i’ve found this forum as i’m looking to sell/re-home this same system from my childhood home. it comes with 4/5 of the bedroom intercome faces – 3 large and 2 smaller. i also have an outdoor system for this. they were super-cool when i was ten in 1967 but honestly – i don’t remember anyone every using it! one of those things that looked much better on a wall. we always just shouted up the stairs of course! email me at

  33. After re-thinking it, how about just replace it with a Raspberry PI application running a HAL-9000-ish type program :) — just don’t put HAL in charge of the pod bay doors.

  34. Not sure if anyone is still following this topic, but….
    I’m in the process of buying a house with a system similar to this. My plan is to remove all of the intercom system leaving only the wire runs. Then, use an amplifier (hooked to an audio source that can be remotely controlled from my android phone) to drive brand new full-range flush-mount speakers that would take the place of the original hardware.

    Does anyone see any problems with this plan? If I’m sure to disconnect the power and intercom system, it should just be a bunch of 3 wire runs to each panel which could carry an audio signal, correct?

    1. >use an amplifier (hooked to an audio source that can be remotely controlled from my android phone) to drive brand new full-range flush-mount speakers that would take the place of the original hardware

      * Wiring continuity — over the years, vermin, people in the attic, abrasion under staples, etc takes its toll. You might find opens or shorts; test and experiment before you buy a whole houseful of expensive speakers.

      * The wiring may measure several ohms round trip (you can measure by shorting all 3 wires at a remote station, then use an ohmmeter at the base to measure round trip resistance. 5 ohms? 20 ohms? It could be, and if so it would limit the power (watts) deliverable to an 8 ohm speaker.

      * The main (base) station was good for only about 2 watts audio power total to all the speakers, and the wiring was sized for that low power delivery.

      * Despite the possible series resistance of (good) wiring, you might still load down a centralized power amp with, say, 10 8 ohm speakers all in parallel.

      * There are two alternatives to an “all in parallel” distribution:

      o The classic “70 volt” transformer-based distribution system used for high power paging speaker power distribution without heavy gauge wire: At the central amplifier output, connect to (say) the 50 Watt tap of the speaker side of a “70 volt”. The “70 volt” side goes out in parallel to all the stations. At each station, connect the “70 volt” side to the line, but on the speaker side, pick a “5 watt” tap. This distributes any power level up to 50 Watts evenly across 10 speakers without saturating the transformers, and gives you ground fault isolation and won’t add any hum. If you’re doing stereo, then it’s two transformers per run, one for each channel. Could get into a bit of money and there will be some bass roll-off.

      o Much cheaper: Get amplified speakers for each remote station. You’ll have to hide the wall warts and power cord runs at each full range speaker. Drive them either with either headphone-level signals directly or a low-output-impedance low gain power amp at the base station and you might not get hum pickup at the remotes, and could get full range audio. Do some experiments before buying a whole set of stuff.

      Long story short, this wiring won’t do for direct distribution of hefty audio power unless you use transformers for impedance matching, else distribute at low power then amplify at each station. And that’s only a go if all the wiring’s still good.

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