Author Topic: Question on 295A Subset Diagram  (Read 3126 times)

Offline Larry

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Question on 295A Subset Diagram
« on: August 08, 2015, 09:18:45 AM »
I am new to this forum and I'm still learning what all the components are that appear in the schematics.  I have attached a diagram of the 295A Subset.  Can someone please tell me what is that component that the leads on C and L2 go to?  It's the very bottom of the diagram.

Thanks !

Larry

Offline poplar1

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Re: Question on 295A Subset Diagram
« Reply #1 on: August 08, 2015, 09:46:02 AM »
It's a capacitor, known at that time as a "condenser." In this circuit, one capacitor serves dual purpose: for the talking circuit and for the ringing circuit. Many later subsets had separate capacitors for these two functions.
"C'est pas une restauration, c'est une rénovation."--François Martin.

Offline Larry

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Re: Question on 295A Subset Diagram
« Reply #2 on: August 08, 2015, 12:01:16 PM »
ok.  So, I reviewed the posting by Sargeguy which details how to test the various components of the 295A using a volt/ohm meter.  Based upon that posting and the ohm readings, this 295A has a No. 20 coil.   All of the components test good. Now I would like to hear the bells actually ring.  I don't have a telephone to connect the subset to.  I'm working on getting one. In the meantime, just for kicks, I'd like to hear the bells. 

Here's what I have I could use.  I have a variac which I can use to apply the correct AC voltage if that's what's required.  I also have a DC power supply I built to use on some DC radios that would supply DC current.  Is there any DC current in telephone??

If I know how much AC or DC current to apply, I can test the bells actually ringing.

Larry
« Last Edit: August 08, 2015, 12:20:26 PM by Larry »

Offline poplar1

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Re: Question on 295A Subset Diagram
« Reply #3 on: August 08, 2015, 12:32:13 PM »
Normal ringing current is 90 VAC, 20 Hz. You would apply this to L1 and L2 as shown in the diagram.
(Make sure the ringer is connected to L1 and C). It should ring even without a phone connected to the subset.

The talk circuit operates on filtered DC. Modern central offices provide 48 VDC, though with the resistance of the outside cables, and of the telephone set, the voltage might drop to around 10 VDC off-hook.
« Last Edit: August 08, 2015, 12:34:11 PM by poplar1 »
"C'est pas une restauration, c'est une rénovation."--François Martin.

Offline Larry

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Re: Question on 295A Subset Diagram
« Reply #4 on: August 08, 2015, 01:36:24 PM »
I would like to connect this WE 295A subset to either a WE 102 or 202.  Is that possible?

Larry

unbeldi

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Re: Question on 295A Subset Diagram
« Reply #5 on: August 08, 2015, 01:52:52 PM »
I am new to this forum and I'm still learning what all the components are that appear in the schematics.  I have attached a diagram of the 295A Subset.  Can someone please tell me what is that component that the leads on C and L2 go to?  It's the very bottom of the diagram.

Thanks !

Larry

As poplar1 already pointed out, it is a condenser, the contemporary name of what is now known as a capacitor.   Electrical components used to be drawn as rough illustrations of their real physical parts, and this resembles the construction of a condenser, namely two electrically isolated metal foils rolled up with an insulating material between them.  Similarly you recognize the ringer and the induction coil.  Over time, these symbol became more abstract, simpler, and smaller to draw easily.

Here is a modern incarnation of the same circuit diagram drawn.
Knowing the construction of a capacitor, you can still recognize the component, the two lines perpendicular to the trace at the C terminal, but interrupting the trace. It resembles two metal plates opposing each other.

I also included in this diagram the arrangement of the telephone set in simplified form, namely the correct connections to the receiver and transmitter. In a real telephone set, which could be a candlestick or one of the desk sets (A-, B-, D-handset mounting), or a wall set (C-, D-mount), there would also be switches (switch hook) to disconnect the instrument from the line.  Those are strategically placed in the telephone circuit based on the manufacturers preferences and the form factor of the set.

From my diagram you might also now recognize that the ringer is really a separate circuit from the audio portion of the telephone.  So you can simply connect a telephone line between connectors L1 and L2 and the set will ring if the components are good.

I labeled the connection terminals to the telephone set with letter mnemonics of the color wires in the mounting cord. Early subsets didn't do that, but starting ca. WW-I it became common practice and these mnemonics were used until the end of the Bell System, and beyond.

Hope this helps.






« Last Edit: September 21, 2017, 03:00:46 PM by unbeldi »

unbeldi

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Re: Question on 295A Subset Diagram
« Reply #6 on: August 08, 2015, 01:59:31 PM »
I would like to connect this WE 295A subset to either a WE 102 or 202.  Is that possible?

Larry

Certainly, I just gave you a hint on how to do it, in my post that crossed yours.

The correct set to connect to this subset is the 102 telephone, which can be either an A1, B1 or a D1 desk set.  The 202 telephone is an anti-sidetone telephone, which is not completely compatible with this subscriber set.
An anti-sidetone (AST) telephone compensates the direct coupling from transmitter to receiver, which has the effect that the speaker hears him/herself too loudly, as well as hearing all room noise amplified. The AST compensation only leaves enough feedback so that the user gets the impression that the telephone is actually working. It requires a subset with an induction coil that has three windings, and a mounting cord with four conductors, instead of the three here.

However, if you already have a 202 set (D1 most likely) with a four-conductor cord, you can simply connect only the red, green, and yellow conductors, and ignore the black one.  The set will work fine, except you won't have the anti-sidetone correction.

The designation 102 and 202 indicate the electrical configuration including the subset.
This forum has many examples for wiring B1 or D1 handset mountings as either 102 or 202 telephones.
 
« Last Edit: August 08, 2015, 02:17:50 PM by unbeldi »

Offline Larry

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Re: Question on 295A Subset Diagram
« Reply #7 on: August 08, 2015, 02:17:18 PM »
All of this is very helpful.  Thanks for sharing this information with me. 

So, 102 with subset 295A has more feedback to the receiver and 202 just enough to know the phone works. I don't have a phone at this point.  I just have the 295A subset in a walnut box.  I believe I've read that subset 684 would be compatible with a 202.  Is that correct?

Larry

unbeldi

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Re: Question on 295A Subset Diagram
« Reply #8 on: August 08, 2015, 02:25:36 PM »
All of this is very helpful.  Thanks for sharing this information with me. 

So, 102 with subset 295A has more feedback to the receiver and 202 just enough to know the phone works. I don't have a phone at this point.  I just have the 295A subset in a walnut box.  I believe I've read that subset 684 would be compatible with a 202.  Is that correct?

Larry

Yes, correct.
The 684A or 684BA is a much later (1930s) type of subscriber set.  The 295s were made until ca. 1916 or so, late teens, I believe, when the 534A steel set came out.

The most period-correct telephone for your set would be a No. 20 or No 40 candlestick.  New dial candlesticks (50AL, 51AL) would probably have been installed with a new 534A subset already.

Offline Larry

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Re: Question on 295A Subset Diagram
« Reply #9 on: August 08, 2015, 06:36:03 PM »
For where I need the phone, I need a dial phone.  So, I'll keep looking for a WE 102.

Thanks for all your time and information !!

Larry

unbeldi

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Re: Question on 295A Subset Diagram
« Reply #10 on: August 08, 2015, 07:01:16 PM »
For where I need the phone, I need a dial phone.  So, I'll keep looking for a WE 102.

Thanks for all your time and information !!

Larry

You're welcome.  There is certainly nothing wrong with connecting a 102, as many of these were refurbished and reused many times throughout the 20s and into the 30s.

How is the condition of the wood of yours?

Offline Larry

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Re: Question on 295A Subset Diagram
« Reply #11 on: August 08, 2015, 11:22:49 PM »
The walnut box of this 295A subset is immaculate and the nickel plated bells are flawless.  Interior and components are in excellent condition and all components test good.  I probably paid a bit more for this subset, but it was exactly what I wanted and had hoped to find.

Larry