140AL Candlestick wiring to RJ11 plug

[Bob Brockway]

Hi,
New guy here and completely new to old phones. I have aquired a 140AL and would like to use it at my house. I connected the wires to an RJ11 plug in the proper order but when I plug it in I get dial tone and can hear the other person but they cannot hear me. I used an ohm meter to trace out the lines and came up with the attached schematic. It doesn't really make sense to me though, it may be wrong. Why would the yellow and black wires just short out to each other? Does anyone have a schematic for these phones?
One thought as to why the transmitter does not work is it is connected to line 2 of the RJ11. Should this be wired to the RJ11 in a different way? I just matched color for color. I read up on RJ11s and it seems that the RED and GREEN are line 1 and the BLACK and YELLOW are line 2. Is that right? I attached a T1 transmitter to it and it still didn't work. I suspect the problem is my wiring to the plug.
Any help is greatly appreciated.
Thanks,
Bob

[unbeldi]

Welcome to the forum!
A 140AL is a nice way to start a phone collection.

And with that you are digging in deep into the operation of telephones. As you discovered, your candlestick contains a transmitter, a receiver, and a hookswitch.  Your resistance measurements show that your components appear to be in serviceable condition.  The resistances of the transmitter and receiver are in line with what to expect.

However, these types of telephones also needed at least one additional component to work properly, an induction coil.  The induction coil is a transformer that performs two functions.  It adjusts the audio impedance of the receiver and transmitter to match the combination of the transmission line (local loop) and the impedance on the central office end, and thereby optimizes the transmission of electrical energy. It also functions as a hybrid to convert the four wires of the receiver (two wires) and the transmitter (two wires) to two wires of the local loop.

The induction coil was provided inside a wall- or deskside-mounted desk set box, or subscriber set (subset).
A typical subscriber set for your 140AL would be a model 634A or a 684A subset.

There are many pictures here on the forum of such subsets, and many discussions on wiring them.

A subscriber set also provided a ringer to alert you to incoming calls.  The ringer circuit is rather separate from the audio part of the telephone and is optional if there is already a ringer on the line.

Your 140AL is an upgraded version of the 40AL desk stand.  The addition of the "1" in front of the model number indicates that it was converted to an anti-sidetone circuit.  Such a circuit eliminates most of the electrical feedback from the transmitter to the set's own receiver, so that the users hear themselves only well enough that they realize the set is actually working, but not too loudly as was the case with previous technology. The goal was to provide just enough sidetone comparable to the experience when talking to person face-to-face. It would be odd if you couldn't hear yourself when talking to someone in front of you.  The anti-sidetone feature was implemented in the Bell System starting ca. 1930, while the 40AL was already used by the mid-1920s.  140s were never manufactured newly, only upgraded during refurbishing.

Because of the electrical intricacy of an anti-sidetone (AST) telephone circuit and the electrical design of the receiver elements by the 1920s, such a circuit also needs at least one capacitor (=condenser) to block direct current from entering the receiver.  Another capacitor is needed for the ringing circuit. Earlier circuits, the sidetone circuits, could work with only one capacitor, but a Western Electric AST circuit required two.

Here is an article that shows a matching 634A subscriber set: http://www.classicrotaryphones.com/forum/index.php?topic=12494.0

The 634A subset shown in that thread uses a 101A induction coil which didn't find widespread distribution until ca. 1935. Between 1930 and 1935 these subsets used a No. 146 induction coil, and you will find examples of that also in the forum.

[unbeldi]

For your reference, here is the official diagram of the 140AL desk stand from a Bell System publication, BSP C63.373 Issue 2 of 1937.

The second diagram is the circuit of a 634 or 684 subscriber set.  The difference between these two is really just the form factor of the package, the circuit is the same.

Highlighted in the second diagram is the induction coil in the broken box, and the mounting cord to the desk stand and the line connections, tip and ring.

You also see the two capacitors, one in the ringer circuit (left side) and one in the audio circuit.  The ringing circuit is connected via terminals L1 and L2, which are physically the same as those of the audio side, but I showed them separately for illustration.

[poplar1]

To clarify, the "connecting block" indicated in the diagram was used to extend the four wires from the subset, up to 250 feet, rather than having an extra long cord on the 140AL/120AL. Neither the phone nor the connecting block, if used, was connected directly to the line.

[Bob Brockway]

Wow! I knew I came to the right place. I really appreciate the detail of the responses.
Can anyone name a good book on these desksets? I would be interested in something that focuses on troubleshooting, repair, restoration, etc.
Thanks again.
Bob

[Bob Brockway]

One more thing. Are the 634A and 684A subsets the only two that will work? I am looking on ebay and want to have other options if they are available. Also, how rugged were these things. I see a lot for sale that are "untested" and being sold as is. If they tended more toward the fragile side I want to avoid the untested ones. If they are pretty bullet proof, I may take a chance.
Thanks again,
Bob

[poplar1]

78A ringer

Anti-sidetone Subsets: (for 202, 211, 140AL. 151 AL, 152 AB)

434A   (conversions only)
     with 146B induction coil    {C31.111, Issue 1, June 1931} (TCI Library)
     with 101A induction coil     {C31.101 Issue 3, July, 1953}  (TCI library)

495BP  (conversions only)--Cow gongs

634A  (Steel) (Conversions only?)

684A  (Bakelite cover)
         with 146C Induction Coil, 78A ringer
         with  101-type Induction Coil, 78A ringer
         
634BA (Steel, high impedance ringer) (Conversions only?)
         
684BA (Bakelite cover, high impedance 78JA or B1A/B1AL ringer)


NOTE: The base of a 302 set can also be used as an anti-sidetone subset.

[Bob Brockway]

NOTE: The base of a 302 set can also be used as an anti-sidetone subset.

This may be the way to go! I'm seeing these on ebay for around 25-30 bucks as opposed to 150-200 bucks for the 634A. I am finding a lot of information on these forums that addresses how to hook these up.
Thanks,
Bob

[unbeldi]

One more thing. Are the 634A and 684A subsets the only two that will work? I am looking on ebay and want to have other options if they are available. Also, how rugged were these things. I see a lot for sale that are "untested" and being sold as is. If they tended more toward the fragile side I want to avoid the untested ones. If they are pretty bullet proof, I may take a chance.
Thanks again,
Bob

These subsets are actually very rugged, and I haven't found one that couldn't be resurrected.  But we have to recognize that the components in these are many decades beyond their life expectancy conceived by the designers.  Occasionally we do find a malfunctioning condenser, but rarely a broken induction coil, more frequently broken wires. Often these were not treated delicately after taken out of service. What is produced today is certainly never going to achieve the longevity of this type of equipment.

Some damage is often done by people who just don't know how to wire these or how to care for them. That includes collectors who often modify them for a purpose originally unintended.  It includes also rather well know collector-types who just sell something for exaggerated prices, and which they have made to look 'nice', but not according to authentic configuration.   Often you will find candlesticks and desk sets with RJ11 plugs that the sellers announce as ready to plug in and use, shiny, costing hundred of dollars, while they are actually simply "hot-wired" in series and over time will be damaged when plugged into a line directly. They usually don't tell you that these require a subset to sound and work correctly.

[unbeldi]

NOTE: The base of a 302 set can also be used as an anti-sidetone subset.

This may be the way to go! I'm seeing these on ebay for around 25-30 bucks as opposed to 150-200 bucks for the 634A. I am finding a lot of information on these forums that addresses how to hook these up.
Thanks,
Bob

Time-period-correct subsets are not plentiful, for sure.  When in need, indeed, a 302 telephone base performs the same function in identical manner.  The circuit of the 684 subset is identical in principle, give and take some wire colors and minor things, to the base of a 302.  The circuit diagram I presented is equally applicable. The condenser in the 302 is a dual-type in one can, while many 634s used two separate condenser cans.  You can even buy a new polyurethane cover for a 302 base that Ray Kotke molds for collectors, and which he sells on eBay frequently. With these, a 302 base looks virtually the same as a 684A subset.

[Bob Brockway]

Thanks guys. I am learning a lot. I also saw the phones that were "hotwired" and never knew it was wrong. That's why I thought just wiring it to an RJ11 plug would work. In reality I only have half of a phone system. Well I just purchased a 302 base on ebay and it should arrive this weekend. I saw several threads talking about how to use these with 4 wire phones and it seems pretty easy. Between that and the wiring diagrams you provided I should be in good shape. I feel myself slipping into a rewarding yet potentially expensive new hobby (don't tell my wife).
Thanks,
Bob

[unbeldi]

Thanks guys. I am learning a lot. I also saw the phones that were "hotwired" and never knew it was wrong. That's why I thought just wiring it to an RJ11 plug would work. In reality I only have half of a phone system. Well I just purchased a 302 base on ebay and it should arrive this weekend. I saw several threads talking about how to use these with 4 wire phones and it seems pretty easy. Between that and the wiring diagrams you provided I should be in good shape. I feel myself slipping into a rewarding yet potentially expensive new hobby (don't tell my wife).
Thanks,
Bob

To be fair to some sellers, but probably the minority, we should recognize that some are building a small "mini-network" into the base of the units. These are small circuit boards, a little larger than a matchbook, with modern components. These are a technically proper, but not period-authentic, solution. They typically emulate a Western Electric 425-type network and some are copied from a design by the Automatic Electric Company.

PS: I found some discussion of that here.

[unbeldi]

And to expand on the theme, some go the cheapest route and add only a resistor and capacitor as what some might call an RC network.  I think I showed a diagram for that somewhere here, but I am not recommending it.
Ok, here it is. At least it does not permit DC flowing through the receiver, but the impedance match to the line is only provided for by an energy-waisting resistor, and there is no signal amplification because it doesn't have an induction coil.

[Bob Brockway]

Allright, I got the 302 base in and wired it per the instructions found on this forum and it works great. Thanks for all the help.

[unbeldi]

Excellent, congrats!

I was wondering, what kind of transmitter and receiver was your set actually equipped with after the conversion from a 40AL?

From your resistance measurements, I am guessing that the receiver was still the traditional 144-type, not the kind that had an HA1 element under the cap.

Is there a number on the front of the transmitter?  I suspect that by the early 30s many 323 transmitters were upgraded with a 337 transmitter (slightly more efficient), and after ca. 1935 with a "bull dog" 635A version, the one that contains an F1 element.