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302 Base With 101B Coil Used As Subset

Started by johnnyjt, March 20, 2012, 07:34:32 PM

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I know a 302 with a 101A can be used as a subset
but can one with a 101B coil?  I tried but no dial tone.


JohnnyJT  8)
South Philly


If you have a 302 with a 101B induction coil, it is really a 304, but the answer is still yes, it can definitely be used.  The 101B induction coil is built around the 101A coil, and is functionally the same, except for a couple of modifications from the 101A which allowed the 101B phone to be used on party line extensions for automatic number identification (ANI).

The 304 is wired slightly differently than the 302, but here is how you should connect to the 304 as an antisidetone subset.

The red line cord wire should connect to terminal L1
The green line cord wire should connect to terminal L2
If you have a modular cord connecting to the wall and it also has a yellow and black wire in the line cord, the yellow and black should be left unconnected, with a piece of tape over the ends so that the ends are insulated.  There will not be enough spare terminals to connect the yellow and black line cord wires to, and the yellow and black line cord wires are extra any way.  (Not to be confused with the yellow and black wires coming from the telephone desk set body.)

Assuming your 304 has a ringer with 4 wires, the wires will be red, black, slate, and slate/red.

The red ringer wire would connect to terminal L1;
The black ringer wire would connect to terminal K;
The slate ringer wire would connect to terminal E;
The slate/red ringer wire would connect to terminal E also.

If your ringer has two wires, red and black, connect the ringer as follows:

Red ringer wire to terminal L1;
Black ringer wire to terminal K

The capacitor under the long metal strap has four wires coming from it  Red, Black, Yellow, and slate.  Connect as follows:

Red capacitor wire to terminal C on the 101B induction coil;
Black capacitor wire to terminal GND
Yellow capacitor wire to terminal L2
Slate capacitor wire to terminal K with the black ringer wire.

The wire from your phone body will have 4 wires; Red, Green, Yellow, and Black.  Connect as follows

Red to terminal R on the 101B coil;
Black to terminal GND where the black capacitor wire is connected;
Yellow to terminal L1;
Green to terminal GN on the 101B coil

Lastly, you will need a jumper wire between terminal L2 and terminal RR on the 101B coil.

That should cover all the bases.

Good luck
-Bill G



Hooked up 304 Base to my 102 and it works perfect!
Yes it has 4 wire bell and it also had which I removed
a 6 wire hook switch from the base.
Other than using the base for a subset I was thinking
of using the coil on my 196G payphone which has none.
Maybe I'll use a 101A coil?

Thank you so much

JohnnyJT  8)
South Philly


I used the 101B coil for on my payphone
to make it 193G back for the 193G top
I have.  Works perfectly.   I used a 101A
to replace the 101B with the 4 wire ringer
304 base.

JohnnyJT    8)
South Philly 


That will work fine because in the 304, the center-tapped coil is no longer needed any way.  Other than the addition of the "M" center tap and the fact that L1 is labeled RR on the 101B, there is no difference in the coils.
-Bill G


Bill, now how would you handle this question with a 104A coil?? could that be used too?


A 104A coil is a local battery coil, and would not work as a common battery subset.
-Bill G


If you didn't care about the originality of the 101B coil, you could clip the little link at M and use it as a tie point for Y-L2, even though you may end up with 3 terminals under one screw.


bill, have you ever looked at the schematics of the 101 and the 104 coils side by side? there is a way to use the 104... I'll let you figure that out.... 


Quote from: Babybearjs on February 05, 2013, 04:41:53 PM
bill, have you ever looked at the schematics of the 101 and the 104 coils side by side? there is a way to use the 104... I'll let you figure that out....  


As you point out, the diagram is similar.  The difference is in the impedance.  Yep, you can hook it up, and yep, it will work, but not optimally.

So, I will qualify what I said, and instead of saying it won't work, I will say that by using a 101a or 101b, the results will be more optimal than using a 104a.

-Bill G


The debate about which coil to use can never be about "will it work or not", but under which circumstances does it operate as designed.  Clearly each coil works when the line conditions are as expected. The key point is to specify the electrical conditions under which it is supposed to operate.  The range of line conditions can actually be rather wide in each case, and this was by design at the labs for obvious reasons.  In the case of the 104, it has an extra loop impedance adjustment in the added 300 ohm resistor in series with the tertiary winding.

That said, the 101-type coils are electrically very different from the 104, however. This is illustrated by the following data compilation:

windingR (Ω)t/ratioR (Ω)t/ratio

P=primary winding; the primary winding is the winding in the transmitter circuit.
S=secondary winding
T=tertiary winding
t/ratio is the turns ratio relative to the primary winding

Therefore, in order to use a 104A with appropriate conditions, one should modify the local loop to simulate a very long line, perhaps by adding 3-5kΩ loss into tip and ring.

The low resistance of the primary for the 104A-type local battery circuit is necessary to keep the energy loss from the battery as small as possible and generate the enough transmitter current with a small battery of 3 cells, which means about 4.5 volts potential.  A CO powered local loop on the other hand is biased at up to 48V, requiring a larger resistance to keep the transmitter current in the proper range of 50-100 mA.


Interesting information.... its funny though.... I have several 307's that I have wired up like the 101A and the audio is just as good as on a 302.... I guess on the new landline circuits the telephones work regardless of the resistance values.... and then.... I'm using the 307's on a "short line" instead of a "long Line"..... if that makes any difference... the main thing is.... then you wire the 104 like a 101, it seems to work the same.... or so this is what I've found.... because we live in a "digital" age, does the new CO technology compensate for the difference on the phones?