Replace flat intercom phone with Old Rotary phone

[kushy28]

Hi Guys,

First post. Be gentle

Long story short, I would like to change our flats BELL SYSTEM (BSTL) OLD 801 intercom handset to a retro style rotary phone for my wife for Christmas. She loves these phones and I thought it would be a great gift!

This is the handset we currently have: "BELL SYSTEM (BSTL) OLD 801" on this site: http://www.intercomsrus.com/intercom_handset_finder_tool.htm

I've opened up both a standard old rotary and the Bell unit and can see that the wiring's are quite different! See the attached images of the standard wiring for both devices.
Had a little stab at matching them up but it's really not going so well so thought I'd ask to see if anyone knows how to match them up or has done anything like this before?

Pictures below (First is the Bell and second is the Rotary)

Thanks in advance for any help given!

[jsowers]

I know next to nothing about intercoms, but your intercom handset looks like a specialized piece of equipment made for the task and a regular single-line wall phone may not work as a replacement. The intercom has a call button on it, doesn't it? I'm not sure what "lock" refers to on the pdf for the intercom handset. It has five terminals with a loop of what looks like 5-pair cable connected to each. Terminals are IROTZ:

Terminals
I Call
R Speech Out (Mic)
O Common
T Speech In (Speaker)
Z Lock

If anyone wants to try, I posted the pdf below. And Bell System--that's not THE AT&T Bell System of yore. This is a company making intercoms using the same name. I just don't think you're going to find something that will substitute for the electronics inside the intercom handset or match the impedance of the transmitter and receiver, whatever they are.

Was I gentle enough?    Maybe someone else has some experience in intercoms like this?

[dsk]

Sinse I do not have any diagrams:
Probably possible without the ringer. You have to locate 2 contact set in the hook switch who opens when hanging up.  Those 2 should be connected between R and the handset transmitter, the other between T and handset receiver. The other t wires from the handset goes to O Between O and Z you should connect 2 wires to the rotary dial contact who closes when the dial is out of rest position.  The last and slightly tricky will be to move the buzzer from the original phone and put it between I and O.  Everything else should be disconnected.

dsk

[Owain]

Z (lock) is shorted to O (common) to release the electromagnetic lock at the communal door. It's usually a 10 - 12 Vac supply, as is the call tone / ringer across I and O. A phone magneto bell might ring; I've never tried it. DSK has the wiring correct in summary.

The original BSTL handsets used small carbon transmitters and these are notorious for failing. Newer replacements use electrets and a small circuit on the circuit board. IIRC the speaker/receiver was a small 8ohm one.

[Owain]

From the 746 telephone:

Remove all straps from the terminal strips

To T16 connect: handset blue wire, handset red wire, dial brown wire (was on T3), and retain one of the bell wires. Connect line wire O common

To T19A connect handset white wire  If you don't have a T19A you'll need to find a pcb track which connects to that side of the hookswitch and link it to T11, along with handset white wire.

To T19 connect line wire R microphone.

To T4 connect line wire I call.

To T2 retain handset green wire.

To T6 connect line wire T speaker.

To T10 connect line wire Z lock.

Rotating the dial off-normal should short T10 (or dial wire 4) to T16 and operate the lock release. Apologies for the apalling diagram. Amended from original posting as I confused hookswitch and dial contacts

[Owain]

The incredibly basic diagram of the BSTL handset is here. Drawn in MouseCAD v.0.1

[andy1702]

If your 746 phone has a press button, you might be able to re-wire that to operate the door lock.

[kushy28]

Guys....honestly this is fantastic help! I was looking for the upvote button but don't think this forum has one or you'd all get one!
@jsowers, gentle as can be lol

Thank you so much! I'll be trying this tonight and will let you know how it goes!

[kushy28]

If your 746 phone has a press button, you might be able to re-wire that to operate the door lock.

I was hoping to operate the door lock with the action of dialing any number from the rotary...not sure that is possible but I'll give it a go based on the mechanism on the two units.

[Owain]

I was hoping to operate the door lock with the action of dialing any number from the rotary...not sure that is possible but I'll give it a go based on the mechanism on the two units.

That should be fairly easy - connect dial brown and orange wires to O and Z as stated. The awkward bit will be finding T19A or T19B for the other side of the hookswitch as they haven't provided tags for those on your phone.

Not stated explicitly so far, but you will need a 5-way line cord.

[dsk]

Ill guess the easiest way to do this is to follow the diagram in this thread. I guess the ringer is based on low voltage mains frequency, it might still be possible to use the ringer motor by putting the ringer coils in parallel. 

Enclosed picture may show how to do do that, you may probably need to turn the gongs to get them closer to the clapper.

You may get hints from this page too:  http://www.samhallas.co.uk/collection/bits_746.htm

dsk

[Owain]

A quick and unscientific check shows that neither a 2 x 500 ohm (in series) Bell 1A nor a 2 x 2kohm Bell 59A will ring on a 12 Vac rated 1 amp supply. They just shudder. Don't know if it's voltage or frequency.

I haven't tried paralleling the coils.

[dsk]

Paralleling makes it fit the voltage, it is still a problem with the frequency, The ring sound will just not be right.
I have an Ericsson pabx ringing at 50 hz, I do not like it! But it rings European phones.

dsk

[Owain]

I do hope Mr Kushy hasn't been assassinated by the neighbours for breaking the intercom system for the whole building ...

[Owain]

Here's someone else who did a similar project with an even older phone (which seems to have been a bit easier - no PCBs to faff about with)

http://www.peterbalch.co.uk/K7867.htm