Wiring A Touch Tone Pad To Any Antique Telephone

By Stan Schreier    ATCA #2561

         A fascinating aspect of collecting antique telephones is that they can be used today, in exactly the same way they were used almost 90 years ago. 'Dialing' a number with a rotary phone is a link to the past.  Granted, the clicking rotary dial is much slower than Touch Tones, but maybe that's a good thing.  What's the hurry?


        Unfortunately, Touch Tones have become more than just a way of routing a phone call from one number to another.  They are used as a method for transmitting information that replaces speech, and sometimes even the human being on the other end of the line.  When the 'talking box' says "Push 1  To Continue in English" there's nothing you can do with a rotary phone that will make that happen.


        I've seen many circuits for wiring Touch Tone pads to antique phones.  All these 'schemes' had one thing in common; they were grossly over-engineered because they went 'by the book'.  They destroyed the original circuitry and with the historic significance of the phone.


        This article describes adding a modern 'necessary evil' to a vintage device.  It outlines in detail connecting an outboard Touch Tone pad to ANY antique telephone in a very 'creative' way that does not destroy the authenticity of the phone.


        It doesn't matter if the telephone is manual, rotary, sidetone, anti-sidetone, candlestick, handset, or wall phone.  There are no added wires running out of the phone.  The Touch Tone pad doesn't have to be near the phone.  In fact, it doesn't have to be visible.  You can hide it in a drawer if you feel it detracts from the antique appearance of your phone.  Only one connection in the phone or subset is changed.  You dial phone numbers just like you always have.  In the event you're asked to "PUSH #", you;ll be able to do that also.





The Touch Tone Pad
        All the Touch Tone pads recommended for this project use integrated circuits and oscillators with crystal or ceramic resonators for frequency stability.
        Make sure the pad you use has a diode bridge (polarity guard) so your finished phone wonít be polarity sensitive.  Figs. 1a-1c are recommended units.
        Figs. 1a and 1b are pads from Premier 2500 phones, made by North Supply.
        Fig. 1c is an ITT #42 pad (my favorite).
        You can use a Western Electric #72 pad, but Iíve been told they have a high failure rate due to poor switch contacts.
        Donít waste your time with the old pot core units.
        Vendors for parts will be listed at the end of the article.




            Fig.1a                                              Fig.1b                                             Fig. 1c


        An off the shelf plastic enclosure is used to house the Touch Tone pad.  Theyíre inexpensive and advertised on the Internet.

        Two completed units are shown in Fig. 2.  I built the white one to use with colored plastic 302s. 

It can be painted with Krylon Fusion paint to closely match the color of your phone

        The black unit looks great sitting next to any standard black desk-set.




Fig. 2




Building The Touch Tone Pad

    Fig. 3 shows the dimensions for the pad cutout.  Mark the outline on the case.  Drill 3/16 holes close to one another along the inside of the lines.  You can use a small pair of pointed diagonal wire cutters and snip between adjacent holes to cut out the window.  Use a file to clean up the edges.  The cutout doesnít have to be perfect; it will to be covered with a panel.




 Fig. 3


        Fig. 4a shows an ITT #42 pad hot glued to the inside of the box.  Fig. 4b shows the top of the box with the pad installed without a panel.




Fig. 4a                                                      Fig. 4b




Wiring The ITT #42 Pad


        Refer to Fig. 5.  Locate the Red/Green and the Black wires.  Connect them together.  Use one of the pad mounting screws as a tie point.  Cut off all the other wires, they arenít used.  No, Iím not kidding!



Fig. 5

        Refer to Fig. 6.  Connect a 330 ohm Ĺ watt resistor between the two push in terminals along the edge of the board.  You can put lugs on the resistor leads, or solder them to the terminals.  The output cable also gets connected to these terminals. 



Fig. 6

        If you use a Premier or a Western Electric #72 pad, refer to Fig. 7 and Fig. 8.  The Green wire (labeled F on the board) takes the place of the left push in terminal on these pads.  Use the mounting screw on the right as a tie point for the green wire (output terminal).  Like the ITT pad, a 330 ohm Ĺ watt resistor and the output cable are connected to the output terminals.  The Red/Green and Black wires are connected together on the left hand mounting screw.  As before, cut off the remaining wires.  Still not kidding!




Fig. 7



Fig. 8

        Refer to Fig 9.  File a notch in the bottom half of the box for the output cable.  Screw the box together and install the adhesive rubber feet.

        The plastic panel is from an old 2500 Touch Tone phone.  I cut it to size then used a four-inch wide, bench-mounted belt sander to get the edges square and smooth.  Double-sided Scotch Tape does a good job of attaching it to the case.



Fig. 9


    That completes the Touch Tone pad.  Now weíll work on the phone.



Plastic Or Bakelite 302

        THIS INFORMATION IS NOT FOR METAL 302s; itís only for plastic or bakelite.  If your phone has a large four prong plug open it and see if the YELLOW wire is connected to either the red or the green wire.   If it isnít, thatís fine.  If it is, make a note of what color itís connected to. 


        Refer to Fig.10.  Open the phone and find the lead labeled X. Itís a YELLOW wire connected to the L2 Y terminal of the 101 coil.  The other end goes to the hook switch.  Disconnect the X wire from the 101 coil and put it under the mounting screw of the cloth strap that connects the plastic top and the base of the phone.

        Find the YELLOW mounting cord wire.  If itís connected to another wire, TAKE THE OTHER WIRE and connect it to where the mounting cord wire THAT IS THE COLOR YOU WROTE DOWN, is connected.

        Take the YELLOW mounting cord wire and put it under the strap mounting screw.  There should now be two yellow wires under the strap mounting screw.  Refer to Fig 11.

        Reassemble the phone.  Itís finished.




Fig. 10




Fig. 11

        Refer to Fig. 12.  Wire the plug with the telephone mounting cord and the output cable of the Touch Tone pad as indicated.



Fig. 12


        Refer to Fig. 12a.  Assemble the plug with both cords running out of the hole in the side.



Fig. 12a

        Fig. 13 is a diagram of a 302 with Touch Tone interface.


Fig. 13


        Fig. 14 is an ivory 302 with the Touch Tone pad attached.  It was wired using the circuit in Fig. 13.




Fig. 14




Metal 302

        The wiring of a metal 302 is exactly the same as the plastic models, except you donít put the two yellow wires under the mounting screw of the cloth strap.  The wires are connected together and then taped.   Refer to Figs.15a and 15b.


        There are some fancy Ďin-lineí insulated splicing gadgets made for spade lugs.  As you can see, I didnít have any.  If you do, use them.  After you connect the two wires together and tape them, reassemble the phone.  Itís finished.




   Fig. 15a                                                                                 Fig. 15b  


        Refer back to Fig. 12 and Fig.12a and wire the four prong plug as indicated.


        Fig. 15c is a 302 with vents, short ears and small plungers that I use practically every day. 

Itís not visible in the picture, but it also has a DSL filter on the mounting cord.  Talk about mixed technology!


        To Continue In English, Push 1.




Fig. 15c




Plastic And Metal 302s With Modular Plugs


        Use the above information to modify your plastic or metal phone.  Since you have a modular cord on your phone, you must use a modular cord on the Touch Tone pad.   Along with the 330 ohm resistor,  connect the YELLOW and GREEN wires from the modular cord to the output terminals of the Touch Tone pad.  Cut off the lugs on the red and black wires; they arenít used.  Refer to Fig 16.



Fig. 16

        You will have to make an adapter to connect the phone, Touch Tone pad, and telephone line together.  The adapter is made from an Ďoff the shelfí duplex telephone jack.  Refer to Fig. 17



Fig. 17

        Open the jack by pushing the plastic tabs on the sides in, slightly.  Cut the wires and label the positions for the phone and the Touch Tone pad as shown in Fig 18.





        Figure 19 is the assembled adapter with the 302 and the Touch Tone pad plugged into it. 

Now, plug the adapter into the telephone line.




Fig. 19




354 Wall Phones


        Refer to Fig. 20.  Locate the Green/Red wire on terminal L2.




Fig. 20



        Fig. 21 is a diagram of a 354.


Fig. 21



        Refer to Fig. 22.  Remove the Green/Red wire from terminal L2 and wire it with one of the Touch Tone wires to the terminal labeled GND.  The other Touch Tone wire goes to terminal L2.




Fig. 22



        Fig. 23 is a diagram of the completed 354 with the Touch Tone interface.



Fig. 23


        Fig. 24 is a 354 with a Touch Tone pad wired to it.  They were wired using the circuit in Fig. 23.




Fig. 24



        Refer back to Figs. 3 and 4.  The enclosure for the Touch Tone pad has a sloping top surface.  For desk mounting, when you glue the pad in the top, you want the high end of the slope to be toward the back (numbers 1, 2 and 3).  That will tilt the pad downward in the front.


        For wall mounting with a 354, the slope should be in the opposite direction.  Glue the pad in the top with numbers 1,2 and 3 near the low end of the slope.  This will tilt the numbers upward when the pad is mounted on the wall.

        A wall mount kit for the enclosure is available.  Vendor information will be given at the end of the article.




Phones That Use Subsets




        For phones that require a subset, the Touch Tone pad isnít wired to the phone; itís wired to the subset.




Sidetone Subsets


        The internals of a Western Electric 534 subset with a 51AL candlestick and phone line wired to it is shown in Fig. 25.




Fig. 25


        The phone could be a 20B, 20AL, 51AL, A1, B1, C1 or D1 mount that is wired for sidetone service.  The type of phone doesnít effect how the Touch Tone pad is connected to the subset.


        Fig. 25a is a diagram of a sidetone subset with a typical manual desk-stand connected to it.



Fig. 25a



        Fig. 26 shows the Touch Tone pad and a 51AL wired to the 534 subset.   Note the terminal that was labeled ĎEMPTYí in Fig. 25 now has one wire from the Touch Tone pad and the RED mounting cord wire from the phone connected to it.  The other wire from the Touch Tone pad is connected to the R terminal, where the Red mounting cord wire was originally connected.                                             




Fig. 26


        Fig 26a is a diagram of a sidetone subset with a desk-stand and Touch Tone pad wired to it.



Fig 26a



        Fig. 27 shows a 534 subset with a 51AL and a Touch Tone pad.  They were wired using the diagram in Fig. 26a.


        If you intend to use an arrangement like this on a daily basis, Iíd replace the old transmitter with an F1 cartridge.  You might want to replace the 144 with a 706 receiver.  The old Ďtalk stuffí is historically interesting, but it really sounds awful!



 Fig. 27




Anti-Sidetone Subsets


        Like the sidetone subset, the phone thatís used with an anti-sidetone subset doesnít change the way the Touch Tone pad is connected.



        Fig. 28 shows the internals of a 684A subset with a D mount wired to it.




Fig 28



        Fig. 28a is a diagram of an anti-sidetone subset wired to a typical desk-set.


Fig. 28a



        Fig. 29 is the same 684A subset with the D mount and a Touch Tone pad wired to it.  Note that the terminal labeled ĎSPAREí in the Fig. 28 now has one wire from the Touch Tone pad and the YELLOW mounting cord wire from the phone connected to it.  The other wire from the Touch Tone pad is connected to terminal L2 Y, where the Yellow mounting cord wire was originally connected.





Fig. 29



        Fig. 29a is a diagram of a typical anti-sidetone subset with a desk-set and a Touch Tone pad wired to it.



Fig. 29a



        Fig. 30 is the working 684A subset, D mount and Touch Tone pad.  The subset was wired using the diagram in Fig 29a.




Fig. 30


500 Series Phone       




Fig. 31


           Fig. 31 is a venerable 500 series phone.  Doing this model was an after-thought.

 I donít consider them to be Ďantiqueí.  However, I received emails from a few 20 year olds that do.  Suddenly I feel antique!


          Fig. 32 is the phone as it was originally wired.



Fig. 32



         Fig. 32a is a diagram of the 500CD.


Fig. 32a



        Refer to Fig. 33.  Reverse the positions of the black ringer wire and the slate/green switchhook wire. 


        If your phone has a modular mounting cord make sure the colors are as shown. The black and yellow modular wires can be connected to the point shown for the yellow mounting cord wire, or the black can be cut off.



Fig. 33 



           Fig. 33a is a diagram of the 500CD with the Touch Tone interface.



Fig. 33a



           Wire the four prong plug as shown in Fig. 34.  The two mounting cords come out of the hole in the side of the plug, as shown in Fig. 12a.




Fig. 34



           The information for wiring the modular cord to the Touch Tone pad and manufacturing the adapter in Figs. 16 Ė Figs. 19 also apply for the 500 series phone.




Only Western Electric?


        No.  The blue Figs give enough general information to wire the Touch Tone pads to any telephone or subset, regardless of manufacturer.  I used Western Electric phones as examples because thatís what I collect.




Sources Of Parts


        1 - For the ITT Touch Tone pads and cloth cords go to:





        Call and ask for Odis.  Tell him you read this article and what youíre doing.  Heíll know what parts you need.  If your phone is a colored 302, you can paint the white enclosure for the Touch Tone pad with Krylon Fusion plastic paint and buy a cloth output cord to match the color of your phone.  Odis manufacturers cloth cords in all the 302 colors.


        2 - For the plastic enclosures go to:




        The model numbers for the plastic cases are:


Black    TK-S.9

White    TK-S.7


        If youíre going to use a Touch Tone pad with a 354, a wall mount kit is available for the enclosure.


        The model numbers for the wall mount kits are:


Black    MT2.9

White    MT2.7



        3 - For the plastic panel and the four prong plugs.


        Unless you have an old Touch Tone phone that you can salvage the panel from, go to:




        Itís a free Yahoo bulletin board, sponsored by the Antique Telephone Collectors Association.


        Iím sure youíll find a source for a panel, the four prong plugs and someone that can answer any question you might have about collecting antique telephones.


        4 - Radio Shack stocks the 330 ohm Ĺ watt resistors and the duplex jacks.




Collecting Antique Telephones


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