Connecting old telephones...

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SSLtech

Well-known member
Joined
Jun 3, 2004
Messages
5,447
Location
Florida (Previously UK)
Here's what I'm considering, and I'm not certain that I'm at all smart enough to know how to do such a thing and have it work right off the bat:

I have installed and modified a matrix-based intercom installation between two rooms. It's a speaker and omni-mic based affair with the mics usually at arms length, and various speakers in the control room in the console meterbridge (three locations for three operators) 3 flush-mounted mics; one on the console at each master section, a 19"-mounted speaker and gooseneck mic at the outboard rack, and speakers and mics all over the machine rooms (2 machine rooms, one cable room and a couple of other places)

It all works marvellously, and it's set up so that any calls into the machine rooms automatically dim any monitors by a user-determinable amount, and direct the comms into the monitors also. -I like it a lot!

However...

There are times when I need a "Bat-phone" hotline arrangement, so that any conversation that requires some discretion (delays, 'covering' for errors, etc... -use your imagination!) are not overheard or delivered over speakers.

Since our facility is not averse to "kitschy" or "form-over-function" approaches, rather than a modern ugly telephone, I thought it might be nice to use a coulpe of old James Bond-style big-ol' RED telephones with a light on them instead of a ringer. This would be akin to the red hot-line between the Russian and American presidents in the old Bond movies.

I don't want to bring the "real" phone network system into these rooms. It's VERY nice to be isolated and unreachable sometimes. I also don't want clients tying up an important hotline because they want to get an outside line because their cellphone battery is flat or whatever... I want a 2-phone hotline that does only one thing perfectly and is useless for anything else.

I don't want ringers, A light might be an idea, but basically I just want to be able to say "hotline" over the intercom and have a private, non-overheard conversation.

Probably nothing more than a series wiring arangement of the two phones and a DC power sounce would work, but are there any other cool things that I can do, or is there a way to light a light on the phone when the far-end handset is lifted, wich cancels when both handsets are either picked up, or both down...?

Anybody got any great ideas?

Oh, anyone got any cool places to look for cool-looking retro phones?

[edit:] Found the perfect thing at oldphones.com:
batphone.jpg


Keith
 
I wired up a "batphone" arrangement just as you describe, to allow private conversations between anchor Rolland Smith and his producer during commercial breaks in live news shows. Let me think about it and I'll try to remember what I did; it's been a few years.
 
Well the phone system runs on -48 volts. The ringer works on 90v AC with about a 30hz cycle. To start I would consider going on ebay and look for a Tellabs power supply. (I work at Tellabs :wink: ). Those old supplies have isolated 48v and a ring generator in one box. I saw one the other day for like $10 and its 2 amps.

The tough thing about signaling is that it is normally done in a very large telephone box called the switch distibution. (like an SS7) IT creates the dial tone, and all the signalling. When you pick up the reciever it activated the internal switch hook on the phone. Basically a momentary /make break switch built into the phone. The other end listens to how many make/breaks are made to determine what you want it to do. (for example the old rotary phone: Instead of dialling a call, you could tap the switch hook to dial. Like if the number was 716-xxx, you tap 7 times pause, tap 1 time pause, tap 6 times pause etc...You loose all of this with out the switching device like the SS7.

The amp is built into the phone system and not the phone. They use to make a setup called a 2 wire private line. Its basically 2 cards that fit into a box simular to a 500 box. I would look on ebay for that too. I would have to dig out my old books to figure out the connections. It was basically a party line. Anyone connected could lift the phone and talk.

The bell vs light is easy. The ring generator is 90 v ac and the cycle is slow. For every cycle of electricity, the CLACKER on the bell inside the phone hits the bell. Remove the bell and insert a AC light bulb that runs on 90v or so.

With all of that said, I seem to remember the TV studio I worked at that used a couple of Line amps (maybe it was DA's) to do the same. One going in each direction. But the phone operate over two wires and not four. I think they converted it, so one pair was the reciever, the other the mic. That should work fine. THe light may still need to be rigged different

Joe
 
Really, it needn't be all that complicated. For one thing, Keef mentioned that he doesn't need to generate ringing voltage.

Here's what I remember from our old two-phone system:

24VDC supply through current-limiting resistor (which also keeps the voice currents from being shorted out by the low AC impedance of the supply).

Phones connected in parallel with supply+resistor.

A simple "off-hook" sensing circuit at each end that energized a lamp when the DC voltage across the line went low.

I'll draw something up later.
 
The nearly-right way, plus signaling, for two phones:
2-fone.gif


Bell phones do not need amplifiers (they predate hollow-state amplifiers). Amps are nice for long runs, like from here to Baltimore; not needed in town.

For long in-town runs, it is nice if the central office battery is fed through a retard coil (choke) to reduce battery and line loading. For two phones in the same building, with wall-power (telephones predated wall-power), a big resistor wil do. A third phone will work, but at reduced gain when all three phones are lifted. Conference calls really need an amplifier.

An unmodified standard telephone, when on-hook, is an infinite DC impedance. No current will flow until you pick-up the earpiece.

In this variation, picking up the earpiece will pull current through the 1K resistor. The voltage from blue to red will change from 0V to ~40V, lighting both lights. This alerts the far end, and also confirms to the near end that the system is alive.

A downside is that this needs a 3-wire line. Common phone cable is 4-wire, partly to allow for schemes like this. In fact this IS how the 5-button phones in our offices are wired. It's worked this way since we got multi-line phones in 1957. Yes, the lights stay on at both ends as long as one phone is lifted; what's wrong with that? (How do I know how the lights work? Well, I once drilled a hole in a wall and the phone cable was on the other side......)

The lamps should draw much less than 50mA. If the rooms are dim, or you have an alternate signal channel like the public intercom, an LED with a 5K-10K series resistor is fine. It is too modern, but easier to find and more reliable than low-current high-volt filament lamps.

The scheme would probably work fine with 24V and 500 ohms.

I've picked a high-nominal current. System gain increases with current. For a 100-foot run, this may be more gain than you want: reduce voltage or increase resistance.

It appears that it would work if the resistor were replaced with "equivalent" lamps. However the cold-surge of an incandescent lamp would tend to weld the carbon mikes. You could probably use two LEDs with two resistors sized for 20mA. Perhaps 24V battery and two 1K 1W resistors.

No support for ringer, because I assume you DON'T want ringer in a music studio. Anyway, good ringer is a lot of trouble. (Tip: half-wave rectified isolated 120V 60Hz will tinkle many "110V 20Hz" ringers, but not at normal sound.) The ringer in the phones (if any) might tink on 50V pulses: if it does tink when you lift the earpiece, you can unscrew one wire or stuff the clapper with paper.

Classic phones do not care about polarity. The mike, earpiece, ringer, switch, dial are all agnostic about polarity. The one exception I know is the first-generation TouchTone keypad, which did not work on reverse polarity. Any modern TouchTone phone should bleep fine on either polarity; but TouchTone or even rotary signaling is way beyond your needs.

If you do use the LEDs, polarity matters. (If you expect the phone company to randomly swap polarity, you can add a bridge rectifier around the LED; for in-house DIY either use your noodle or flip the LED until it lights.)

Grounding a short in-building phone system is optional. It will work without ground. In a music studio, it should work cleanly. There is some chance that a hot phone line with ill-defined relation to studio ground will radiate into other signal paths, which could be a disaster if you are bitching about the talent or the boss. Run the red and green twisted; it should keep its signal to itself. If not, re-consider your routing (telephone should not be in the studio-mike conduit). Ground one side, but that may make things worse. You could try center-tapping the red and green with maybe two 220 ohm resistors and grounding the CT; that also reduces level a bit. Do some shout-tests before any critical bitch-sessions.

The power supply could be some existing supply, though crosstalk is an issue and not many 48V supplies have 50mA to spare.

The illustration uses a magneto and a muffler instead of a battery/wall-wart and a resistor.... not gonna hunt for clip-art.
 
Okay, -so I nearly had it figured out, but not quite. -I'm indebted to you!

-From the diagram I conclude that the ringer is AC-driven and across the line on-hook... Not that it matters in this instance.

I can get a 20-0-20VAC transformer and rectify it to more or less 48V. I might try 24V first. -Right now it's off to get a couple of old 500-series phones on eBay... Big red ones, with "Commissioner Gordon" stamped on them if necessary! :wink:

Keith
 
PRR is always a tough act to follow, but since I've already taken the trouble to draw this up:

Batphone.png


When the phones are on-hook, the green (tip) line sits at +24V and Q1 and Q2 are off, since the bases are at the same potential as the emitters. When either phone goes off hook, the green line goes low and the transistors turn on.

The base resistors R2 and R3 may need to be adjusted depending on off-hook voltage, transistor beta and desired lamp current. I specified 4.7K as a starting point assuming an off-hook DCR of about 180 ohms for each phone, minimum beta of 100 for Q1 and Q2, and minimum desired lamp current of ~120mA. (A #1477 24V lamp, for instance, is spec'ed for 170mA of current).

You might wanna use 10K trimmers in place of the base resistors and just dial it in. Adjust the base resistance for best brightness with one phone off hook. The lamp will dim somewhat with both phones off hook, so you can look at it as a three-state indicator: off: all is well; on: pick up the goddamn phone; dim: you've picked up the goddamn phone and I'm yelling at you. Use the largest value of resistance that gives satisfactory lamp brightness, since too little resistance will load the audio currents riding on the line.

I used incandescents instead of LEDs because a good ol' filament lamp still grabs your attention better than a dinky LED.

The 24V supply is drawn as a battery, but it can be any clean 24V supply. At the TV station, we had a number of large rackmount 24V supplies that were used to run relays for tally and on-air lights and a Batphone system like this one. (The Batphone had its own supply, natch).

The fourth wire (yellow) is not absolutely necessary but ya might as well use it since it's there... Less resistance for the lamp + phone current to pass through. Or, if you feel like gilding the lily (not really necessary for a short run, but fun), you can do a balanced-to-ground implementation:

Batphone2.png


Paul will correct me if I'm wrong, but I believe that these slightly more complex circuits posseses a slight advantage 'cause the lamp currents do not pass through the phones' holding coils, and you have greater latitude in which lamps you select and how hot you choose to run them.

Hey, did you end up putting some sort of presence circuit in your intercoms? How'd it work out?
 
This is one of the reasons I like this forum so much. Someone comes in with a need/idea that may be a little strange at first glance, but makes perfect sense. Others think about it a little and post solutions to the problem based on experience and well reasoned thought. Some modification may ensue as the idea developsthen it's off to build the idea and see just how it works.

I get a great deal of enjoyment reading and learning here. I just wish I had more to contribute actively.
 
> I conclude that the ringer is AC-driven and across the line on-hook...

Yes, but blocked by a capacitor so the on-hook phone does not draw DC current.

This is all a bit of a fiddle anyway. Remember that phones were in wide use before signaling, the signaling was added-on bit by bit. A DC-powered ringer might be simpler, but conflicts with the off-hook detection.

It is possible to connect two phones in series. The power supply then must carry signal current: not usually a problem. The DC voltage is critical because the mike current is then limited by battery voltage, phone resistance, and line resistance. Anything changes, gain changes. So it was necessary to start with a high voltage and a fixed resistance to swamp line variations.

Ringer was probably the first add-on that survived. By this time we had medium impedance phones with line resistance that varied a lot. The phone is cut-off by the hook switch, but the ringer is across the line. It is high impedance so line resistance does not matter much. It is on the other contact of the hook switch so lifting the hook WILL kill the darn bell.

As private lines converged onto switchboards, it was nice for the operator to know if a line needed attention. The resistor in the plans above would actually be a "drop relay", a hi-R coil that moved a little flag when DC current was pulled in the line. (The Bell system phone switchboard predates good teeny lamps.)

Ring tone was made with a hand-crank magneto, just like the one in my sketch. In various systems it was turned by the caller, the operator, or a common continuously-turning ring magneto fed a bus to all the operators in a large switch room.

Then there came the undertaker's wife's hatbox. The Bell System did NOT adopt that. But it proved to be key to expanding the small-market low-profit non-Bell phone systems that were sprouting up all over. In time Bell had to adopt the Strowger switch... heck, Bell was buying-up failed phone companies and inheriting a lot of Stroger gear.

Almost none of this was invented by AG Bell. What he really invented was a Phone Company, and he did OK with that. Most of it (including practical mikes and earpieces) was invented by others, but adopted into the Bell System. It was a patent mess too. Bell didn't feel real comfortable with dial systems intil they invented the Crossbar to replace the hatbox, and ultimately TouchTone to get completely away from dial systems (except Bell made you pay more for TouchTone, so they had to maintain the Crossbars until the computer switches became practical).

But you don't want all that crap. What you want is the equivalent of a servant-phone: the Mistress can call the Butler without anybody hiking to the other end of the mansion. Systems like this, and longer ones so you could call the butcher (the butcher could have a dozen phones, one per rich customer), were Bell's original product.

That reminds me....

> our facility is not averse to "kitschy"

Why do you need electricity at all? One big downside of Bell's work is the abandonment of the Speaking Tube. The Butler would get his orders over a speaking tube. They survived on ships through WWII, but those electric phones replaced them everywhere. What you need is hard-wall pipe with sweeping bends, short lengths of flexible semi-rigid hose, and funnels. Conduit and car parts. If you need privacy, stick a cork in your end. If you need signaling, put a whistle in the cork. Totally user-powered. And a specific advantage: they do not accept nor cause ANY electromagnetic radiation.
 
[quote author="PRR"]> Why do you need electricity at all? One big downside of Bell's work is the abandonment of the Speaking Tube. The Butler would get his orders over a speaking tube. They survived on ships through WWII, but those electric phones replaced them everywhere. What you need is hard-wall pipe with sweeping bends, short lengths of flexible semi-rigid hose, and funnels. Conduit and car parts. If you need privacy, stick a cork in your end. If you need signaling, put a whistle in the cork. Totally user-powered. And a specific advantage: they do not accept nor cause ANY electromagnetic radiation.[/quote]

I traced a horrible bleed problem in my studio to some empty condiuts between two of the control rooms, intended for additional tie lines that were never pulled. They were exactly as described: hard-wall pipe with sweeping bends. I could easily talk to my assistant in the other room about 30 yards away.
 
We are the official supplier of CE and UL approved speaking tubes for use in embassies in non-friendly nations.
These speaking tubes are insured and absolutely resistant to all forms of electronic bugging, and are impervious to RF interference, jamming and are guaranteed to continue working perfectly in total darkness and without electrical power.
Our 'Diplomat' range is forged in uni-directional oxygen-free copper with machined speaking bells and natural cork secrecy plungers.
The 'Ambassador' range has the improved clarity of 4 micron gold plating and a new superior manufactured fibre secrecy stopper, secured with a silken cord.
Use for anything other than speech transmission invalidates guarantee.
:shock: :guinness: :guinness: :guinness: :guinness:
 
This all reminds me of the "whispering arches" in front of the Oyster Bar in Grand Central. It's pretty freaky the first time you try it, although it makes perfect sense acoustically.

February 08, 2005
The whispering gallery of Grand Central Terminal

Among the secrets of the Grand Central Terminal is the "whispering gallery" in front of the famous Oyster Bar & Restaurant. There is no sign marking the gallery or how to make it work. But if you wait a few minutes, a couple will undoubtedly walk up and head to separate corners and elicit its magic.

The low ceramic arches, built for the 1913 opening of Grand Central, are designed in such a perfect way that if two people stand at diagonal arches and whisper into a corner, they should be able to hear each other as if they were face to face ? not far across the way.

"I was raised in New York and my father taught me about it when I was just a little, little girl," said Catherine Wiley, who was visiting recently from Brookings, Ore. On this trip, she was traveling with her boyfriend, Ed McDonald, and she brought him to Grand Central to show him the trick.

It?s also a popular scene for marriage proposals. "I see them all the time," said Mary Sitter, a hostess at the Oyster Bar. "There?s a lot at Valentine?s Day."

Sitter, who grew up in Queens, is also a good gauge of how few people know the secret of the arches. Until she started working at the Oyster Bar, she knew nothing of the whispering arches. "I?m a New Yorker and I hadn?t ever heard of this."

So how does it work?

"The voice actually follows the curvature of the ceiling,? said urban historian Justin Ferate, who leads tours of Grand Central. It?s called "telegraphing."

The arches were designed by a father and son team, Rafael Guastavino and Rafael Guastavino Jr. Their work has become a signature style for the city, found in hundreds of places, such as in the Great Hall at Ellis Island, the Cathedral Church of St. John the Divine, St. Paul?s Chapel at Columbia University, the space under the Queensboro Bridge ? which can be viewed from the pricey Guastavino?s restaurant - or next door at the Food Emporium grocery store.

The acoustics of the Guastavino arches have fascinated many people, according to architecture critic Francis Morrone, who is working on a book about Grand Central Terminal. Jazz composer Charles Mingus not only liked to play his bass under the whispering arches at Grand Central, but he also proposed to his wife there, Morrone said.

The acoustics of the arches can hold other surprises ? especially for diners at the Oyster Bar, which also has Guastavino ceilings. It?s not the place you want to go if you have any secrets to discuss. "We?re still finding spots in the restaurant where your conversation carries across the room," Sitter said.

Posted by Amy at February 8, 2005 10:16 AM
 
Sound tubes were in use on US Navy ships through the 1980's and were a required element of training. Since this was brought up, it reminded me that sound powered phones are also readily available for this kind of application. No power is required to run the hand sets and you can have a crank call box. They are used still in mines, ships and some industrial applications. They are certainly not high fidelity but they are simple and work reliably without extrenal power.
 
Ah. That's perfect! -Finally ANOTHER reason to smash this French horn up, and used the rotary valves for an intercom!

-It's from when I used to date a girl who played the French Horn... -I always found her kisses to be a bit odd,

...but I *LOVED* the way that she held me!!! :shock:

:wink:

Keef
 
> a simple PBX can be fashioned using a rotary valve

I wuz gonna say: trombone! But SSL beat me to it.

> Sound tubes were in use on US Navy ships through the 1980's

Not surprising. Sailors distrust electricity, and through the 1940s the state of electric cable was not to be trusted too far out to sea. Ships built then, or on similar plans, sure would have served through the 1980s, and the protocol would have to be taught to all sailors until all speaking tubes were cut-up and scrapped.

Apparently TedF has done the research for a UL tag. There are some issues: poison gas can be spread through speaking tubes. Flame is unlikely in a long metal tube, but possible in some situations. Electric telephony avoids these risks, but adds electrocution and failing at the worst possible time.

I've always wanted to do a monograph on speaking tubes. While the Navy may have moved on, there are people like Old House Journal who might find it interesting. Though I have not seen a residential speaking tube, they must have existed, may still be lurking in walls, and would be a "charming" and practical restoration. Damsite cheaper and cleaner than restoring an old fireplace.

The acoustic properties are fascinating, open to computation, except some data has to be got by experiment. Mock-up some tubes and a couple artificial heads. But my gut tells me that electrical conduit, with bends but without junction-boxes, plus heater hose and oil-funnels, will give good performance over runs longer than any house.

Oh: while a multiplexer is possible and easy, I think (Thomas may confirm) that it was about as simple to have a bunch of speaking tubes. Butler, Maid, Parlor, Chauffeur's Lounge, Mess Hall, Engine Room....
 
The speaking tubes aboard ship were reserved for what was deamed "vital communication". They went from pilot house to engine room, pilot house to radio room, pilot house to captain's quarters, pilot house to combat center. Depending on the type of ship there were other runs as well, like to the admiral on battle ships or aircraft carriers auxilliary steering, troup headquarters on amphibious ships.

The tubes are made of brass (polished daily of course) about 3" in diameter with belled ends and stoppered with a wooden plug (usually decorated with elaborate knots). The fidelity was not good usually and you had to shout to be heard. Since I lost most of my hearing due to Naval guns and no adequate hearing protection and wore hearing aids, these tubes were not my forte. Sound powered phones were much better.
 

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