A Simple Automatic Ringer Control For Magneto Phones


                                   by Stan Schreier  ATCA #2561


One of the first phones I found when I started collecting was the Swedish American pictured below.  I can still remember carrying it to my car, a 1966 Mustang and putting in the trunk.  That was in 1967 or 1968.  The Mustang is long gone but I still have the phone. 



A few weeks ago I took it down from the top shelf in my workroom where it had been collecting dust for years.  My intention was to display a Gray coin collector mounted to it and also find out why the magneto wouldnít ring the bells.


I got two surprises when I started working on the phone.  The first surprise was that the ringer had been disconnected.  The second was a diagram slid in back of the magneto for a simple ringer control circuit that I drew almost 40 years ago.  The circuit rings the phone on incoming calls or when the magneto is cranked.  It also isolates the phone line from the magneto.   I havenít thought about this circuit for over 30 years.     


After my walk down memory lane I decided to build the circuit for the phone and Ďold time sakeí.  Iím sure it had one in the past.  That was the reason for the diagram and the ringer being disconnected.  I probably took it out to use in another phone and didnít get around to building a replacement.


Iíve never seen a circuit like it published.  But, then again I wasnít looking for one.  Since itís very simple to build (only 3 parts) and solves all the problems associated with connecting a ringer to both a phone line and a magneto, I thought it would be of interest and worth writing about.



The Circuit


            Refer to Fig. 1.  The circuit has three parts:  a relay, a diode bridge and a capacitor.  When the magneto is cranked, the relay closes and switches the ringer from the phone line to the output of the magneto.  When the magneto isnít being cranked, the ringer is connected through C1 and the normally closed contacts of K1 to the phone line.  Told you it was simple.







Fig. 1.



Building It


            Since all the parts can be connected directly to the relay terminals I didnít bother with a printed circuit board.  Build the unit using the illustration in Fig. 2.  Five different views of the completed assembly are shown in Fig. 3- Fig. 7.  Use double-sided tape to mount it in the phone.



Fig. 2






Fig. 3                                                                                          Fig. 4




Fig. 5                                                                                          Fig. 6




Fig. 7



Finding Parts


  Radio Shack stocks 2 of the 3 parts needed to build the circuit.  The relay was found in surplus from a very interesting source.  The founder was an engineer with the Lincoln Telephone Company in the 1920s.  It seems the surplus business was a result of his early involvement with the telephone industry in Kansas.


This is a list of the parts and suppliers. 


                        C1- 1 mfd  250 volt capacitor



D1- Full wave diode bridge



K1- 110V AC DPDT relay              



          Take a look at the history of the Burden family.




The relays are a bargain at $0.95.  Unfortunately they arenít new and were pulled out of equipment.  I bought six and ended up with four good ones.  I suggest you buy a few extras, just in case.  Theyíre cheap enough and youíll probably pay the same amount for shipping and handling anyway.


If you donít like buying surplus, or are independently wealthy, McMaster-Carr stocks a suitable relay.  The part number is 7098K15 on page 875 of their on-line catalog.





Testing The Unit


          Testing the unit is straightforward.  Connect the green wires to the output of the magneto, the red wires to the phone line and the blue wires to the ringer.  Watch the relay and turn the crank.  The bells should ring and the relay should energize.  Call the phone line you connected the red wires to.  The bells should ring and the relay should stay de-energized.   If all this happens the circuit is working fine.  Now, wasnít that easy? 




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