Western Electric d-1(202) with or without Subset

[southernphoneman]

Hi I am sure somewhere there is a thread on this subject but can someone please re iterate to me what the consensus is on plugging a WE 202 straight into a wall without the proper subset versus with the subset, it was my understanding that the subset is needed to operate the phone properly and not do any damage to the phone, thank you, Gregg

[Phonesrfun]

The subset keeps DC out of the receiver and limits the current in the transmitter.  Connecting the receiver and transmitter in series across the line puts the receiver in the DC path which can demagnitize its permanent magnet over time.  Other issues are that the volume in the receiver will not sound good.  It is just not the way a phone receiver and transmitter were designed to be operated.  Too much current through the transmitter is also not good.

If you don't have the resources for a subset, you can achieve nearly the same results as a sidetone subset and not damage the receiver and transmitter with a simple resistor and capacitor circuit that will cost just a couple Dollars.  It can easily be built right into the base of a B or D mount (102 or 202) base.

I don't have a way to scan that, but if you search the forum for something I posted a couple years ago titled "Cheater Subset" you can see how simple it is.  THe resistor limits the current and splits the voltage between the receiver and transmitter.  The capacitor keeps DC out of the receiver.

The 2 MF 250 volt capacitor is the hard thing to find.  I have a couple of these I can send.

[southernphoneman]

The subset keeps DC out of the receiver and limits the current in the transmitter.  Connecting the receiver and transmitter in series across the line puts the receiver in the DC path which can demagnitize its permanent magnet over time.  Other issues are that the volume in the receiver will not sound good.  It is just not the way a phone receiver and transmitter were designed to be operated.  Too much current through the transmitter is also not good.

If you don't have the resources for a subset, you can achieve nearly the same results as a sidetone subset and not damage the receiver and transmitter with a simple resistor and capacitor circuit that will cost just a couple Dollars.  It can easily be built right into the base of a B or D mount (102 or 202) base.

I don't have a way to scan that, but if you search the forum for something I posted a couple years ago titled "Cheater Subset" you can see how simple it is.  THe resistor limits the current and splits the voltage between the receiver and transmitter.  The capacitor keeps DC out of the receiver.

The 2 MF 250 volt capacitor is the hard thing to find.  I have a couple of these I can send.

Thank you Bill, this is the answer I was hoping for, there is an ebay seller, who wrote a review on what to look for when buying a 202 and he claims  that you can plug it in straight into the wall and I had emailed him about inquiring why he would claim that, I just wasn't sure of the exact technical reasons but you actually cleared that up for me thank you once again Bill, Gregg

[Phonesrfun]

Some people think that just because you can connect it where the receiver and transmitter are in series, and get a dial tone, it must work.  That's a little like saying who needs tires if you can ride a bicycle on its rims.

[unbeldi]

Here is a principle circuit diagram for such an RC-network.

However, presenting it doesn't mean I am recommending it.
The resistor value in this is a starter value, a guess really. It depends on the loop the circuit is connected to and should be adjusted to tune the off-hook loop current to a reasonable value, say 50 mA.

The circuit is an illustration showing the principle, using a simple desk stand without a dial. But a dial telephone can be used as well. The mounting cord conductor colors in this diagram are the standard ones for all WeCo mountings.

The induction coil network should be used instead, it provides proper impedance matching to the telephone network. It is quite easy to find a 101A induction coil on eBay. Sometimes sellers offer batches of several of them for $10 to $20 and the connections are just as easy. In fact it is even easier. Using an induction coil a capacitor is not strictly needed. In addition the coil can provide anti-sidetone operation with an additional capacitor.

[Phonesrfun]

Yes, that is the circuit.  

I have found that resistor values are not too terribly critical.  You won't normally find a 250 ohm resistor, so a 220 or 270 ohm work pretty good.

[unbeldi]

For comparison, here is the induction coil circuit for the same mounting base.
This uses the Western Electric 101A induction coil.  That is really all that is required to construct a sidetone circuit using a three-conductor mounting cord to the desk stand.

The reason that no capacitor is needed, is that the circuit does not expose the receiver to direct current of the local loop. The receiver only receives the audio frequency signal from inductive coupling between the primary winding (P) of the coil to the secondary winding (S) across which it is connected, i.e. an audio transformer in operation.

The problem with the circuit as shown with a three-conductor mounting cord is that the speech signal from the transmitter also passes through the primary induction coil winding and is transmitted into the speaker's receiver just like the remote audio from the other end of the line. This is what is called sidetone, the speakers hear themselves in their own handset very loudly.

Anti-sidetone telephones have four conductors in the mounting cord. The additional lead is usually black and is connected to a capacitor on the C terminal.

[unbeldi]

The last step in this circuit is the completion of the sidetone (ST) compensation, called anti-sidetone (AST) operation.

Anti-sidetone telephones have four conductors in the mounting cord. The additional lead is usually black on WeCo apparatus and is connected to a capacitor on the C terminal.  The C terminal is the third winding (T) of the 101A coil which is switched opposite in phase to the secondary and is connected back across the transmitter to compensate the sidetone by partial cancellation.

This does also reduce audio transmission, but Bell dimensioned the circuit components for overall proper balance for best user experience.

Since this now provides a path of DC through the receiver, the receiver is protected with the capacitor on the C terminal.  In addition this extra path needs to be interrupted when the handset is placed on-hook, because it would provide a permanent current path through the telephone, loading the local loop fairly heavily and limit the ringer capacity of the line, as well as reduce audio from other party-line members, if present. Therefore anti-sidetone telephones need an extra hookswitch contact, here labeled as HS3, which is connected through an extra mounting cord lead.

Now you have the basic circuit for all of the Western Electric 200 and 300 series common battery telephones.

[southernphoneman]

Perhaps a moderator could edit the title of this thread to replace the word "handset" with "subset", as intended, so searches will produce a better result in the future.

yes if a moderator could that would be great because subset is what I meant to say, Gregg