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Local Battery to Common Battery Conversion project paper

Started by Phonesrfun, February 17, 2011, 12:08:17 AM

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Attached to the bottom of this post is a pdf file that anyone can print out and either use for information purposes or actually build.  I built the circuit and I can say that it works great with several of my magneto local battery sets.

This circuit is made to work with a functional local battery set such as a wood magneto wall phone, or a candlestick that uses a local battery subset with a magneto.  When I say functional, I mean that the transmitter, receiver and wiring need to be intact, and not a phone that has been cobbled up.

It is designed to not invade or rewire in any way the original design of the phone and thus will preserve the phone's local battery identity.

The basic design is such that the interface supplies local battery talk current through a wall wart, and interfaces to the LB line through a 1:1 audio transformer.  A relay senses when the local battery phone goes off hook and switches the interface transformer in between the common battery line and the phone.

The basic design is best used without trying to rewire the ringer or the magneto circuitry.   Besaides, doing that may neccesitate changing the circuit, which some may not want to do.  Thus, it is best to leave the ringer out of the circuit and rely on another nearby phone to get ringing.  While the basic talking circuit was generally the same with all LB phones, the switching of the magneto, and how the ringer was bridged across the line was done in a variety of ways.  If you are competent at LB phones, of course you can install this in a variety of ways.

Even if you are not up to building such a circuit, you may want to download it, print it out, and read it.  The paper was written by Colin Chambers, and he has made it available in the public domain free of charge.

I believe he plans on being at the Southern California show in Placentia to discuss this with anyone who is interested.

Colin's web site is ( dead link 03-18-22 ) and he has a bunch of other information on his website about telephones, and his experiences in the industry.

Cheers and enjoy,

-Bill G


Great job Bill and Colin, it looks to be very thorough and easy to follow.
Thanks for taking the time to do this impressive and professional project.
Hopefully it will end up in the TCI Library too.


An excellent and informative treatise, Bill.  Congratulations to both of you for what will undoubtedly be a great asset to the collecting community.


Now how would convert common battery to local battery complete with ringing, with a seperate magneto, or disconect the internal reinger and get a ringer box.


 Thanks, Bill and Colin.
                    Somehow I ended up with a local battery American Electric - 200 wooden wall set.
I talked to Bill about the LB to CB conversion that he and Colin worked on and I decided it was the best way that I could use this phone without any drastic modifications !!! After I obtained  ;D  the parts and after some thought, reading the diagram, I had it put together and it worked very well. Bill gave me a call ,to hear how the phone sounded, and he said it sounded real good. Here is a pic of the finished board.  I'm still trying to clean up the phone . I'll post finished pic when done!!
                   I'm building a couple of fake batteries , to put the LB to CB board in one and a ringer control by Stan Schreier in the other. I'm almost done . I hooked it all up again and it still works great.
                    I would like to say THANKS , Bill and Colin, for taking the time to make this available to anyone who would like to use it. I apprecitate it greatly!!!!!!!!!!  stub
Kenneth Stubblefield


What a spiffy idea of putting the circuits in fake dry cells!

Can you tell us more how you did that?  Do you have pics of the construction of them?
Adam Forrest
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C*Net 1-383-4820


                I will e-mail pics and links to anyone who wants to make these batteries.   stub
Kenneth Stubblefield


Nice project.

Here are some of the labels for Telephone Service that I have digitally restored

Dennis Hallworth


The cool thing is that if you have a local battery phone that would work if it were connected to a LB line, and otherwise has not been modified, here is a way to put it to use, and maybe even impress your friends.  Either that or they will all continue to wonder about your sanity as a collector  ;D

The circuit really works, and Stub has done a great job with it.

-Bill G


VERY clever, especially including mounting the circuit in a "fake" battery. 

In the photo of all those batteries, what's up with the one on the right, with the "new Bell" logo on it?  That logo came in around 1970.  Were there still local battery magneto phones in the Bell System at that point in time? 

BTW, I call cellular phones "local battery telephones" because they depend on their local batteries to function.  And when people ask what I'm talking about, I give them the brief lecture about LB vs. CB. 


Good point, GG.

I'd Like to see a cell phone with a hand crank coming out or the side for a magneto.  On the other hand, someone will probably come out with an AP for that too, if they haven't already!
-Bill G


Quote from: Phonesrfun on December 12, 2011, 03:02:47 AM
Good point, GG.

I'd Like to see a cell phone with a hand crank coming out or the side for a magneto.  On the other hand, someone will probably come out with an AP for that too, if they haven't already!
Not so wierd. There was a model a while back from Motorola which came with a crank recharger - one snapped its battery into the recharger and used it to recharge the battery. I have one over in the museum, but don't recall its model number. It is a 1990's analog model.

The Telephone Museum of Prince Edward Island:
Free Admission - Call (902) 651-2762 to arrange a visit!
C*NET 1-651-0001


There are a number of crank-rechargers for cellphone batteries.  Freeplay is the #1 maker of all things crank-driven: radios, flashlights, and cellphone rechargers.  A lot of other emergency radios have cellphone recharge capability built in. 

Though of course it takes more cranking to charge up a battery than to operate the drop-signal at a manual switchboard.  OTOH you can crank-charge one battery while talking on the other battery. 


Has anyone actually used one of these? I bought a crank radio for emergencies, but have never gotten it out of the box. How long do you have to crank to charge up a battery? I'm guessing well north of an hour, which seems a bit tedious.



             Here's what I did for power and line-in box. This is an old AE connecting block . Now I need to find a 4 conductor cloth cord somewhere in the basement.  ??? More pics when I finish.  Yes , the black and yellow line-in wires are disconnected ;D     stub
Kenneth Stubblefield