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N717CG questions from a new member

Started by jhutzler, November 08, 2014, 02:01:27 PM

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unbeldi

#15
I have been trying to resolve the discrepancy of model numbers between N717CG and N1717CG and have come to the conclusion that this must be the same difference that WECo created when in comes to catalog numbers w/r/t to equipment labels or stampings.  For example, they used to list a 295 subset as 1295 in the catalogs.

Here we see that the telephone is clearly labeled N717CG on the wood, while the catalog entry is 1717.  I checked the catalogs I have available and they don't show just a 717. Neither do they show just a 417, or 517. The first catalog in which the 700-series appears in is 1955 (T8), while the 1947 catalog (T7) only has 400- and 500-series magneto telephones, which I believe still use the No. 113 induction coil.

The NECo card catalog of 1970 or so only shows a N717-type, apparently long discontinued without replacement.

unbeldi

#16
Quote from: jhutzler on November 08, 2014, 06:36:07 PM
Do you know why the button (N1P?) makes a brief dial tone for a second then nada... the handset is dead as usual unless someone answers a call on the wireless phone first... then the old phone works great?

To answer that you have to verify the wiring of the set.

It sounds to me that your exchange (or is it a voip adapter?)  is seeing the switch action as a dial pulse and therefore seizes to send dial tone.  This is in fact the expected behavior, this is how the original telephone recognized that someone wanted to call.  Only now the exchange/ATA is expecting more digits and therefore you only hear silence (in case that silence can actually be heard).

Clearly your phone has an issue with signaling only.

Perhaps the key is miswired or the key springs are bent out of shape and make the wrong connections.  Please examine it closely and verify that it actually makes the connections as shown in the circuit diagram.  Perhaps you can take a high-resolution picture of it each, before the button is pressed and when it is pressed.


dsk

If we say the The N1717GC are the right diagram: The button works as intended, when pressing the button you short ring and tip or L1/L2 as in diagram, and connects the inductor between ground and the shorted lines. This made it possible to ring the exchange without ringing the ringers on other phones on the same line.
Here you just short the line (no ground wire), and this are telling the  adapter or exchange you are off hook (DC runs)
When you release the button the dial tone stays for a fraction of a second.

By shorting the capacitor, you makes it possible to open a dc current hopefully big enough to signal off hook when you go off hook.
The drawback are the ringer will loose the capacitor, and needs to be disconnected to just test this.

The next steps will be to put in a new, or move the old capacitor for use on the ringer. At last preferable but not absolutely a must, to put in a capacitor in series with the receiver element just to block every little milliamp of dc trying to weakend the magnet.

dsk


PS
I guess it is there, but I can not see the capacitor(s) on the picture.
DS

jhutzler

#18
Ok Guys... thanks so much for your helpful advice.

I feel very humble to admit the white wire on the hookswitch was not on C1 as it should have been but instead was wired to C2. When I rewired ... presto, I have dial tone.

I have disconnected the Magneto as recommended and currently one side of the cap is not in use... the yellow and slate leads.

Minor problem... the ringer rings once everytime I lift the handset off the cradle (hookswitch).  I've read that isolating the reciever from the DC would help but isn't this already the case with my phone if I'm reading the schematic right.

Cheers  ...  Jeff


unbeldi

#19
Again, the first action is to verify the circuit.  Nothing matters until this is confirmed.

Another fact is that you cannot initiate a phone call from this phone on a modern telephone line.
However, you can simulate the "operator behavior" if you use a voice-over-IP ATA that has an automatic ringdown feature, also called hotline feature.  Such ATAs automatically dial a certain telephone number when the user takes the telephone off-hook.  With this telephone you would push the button to activate this.  Of course this way you can only call one number.

So, we really only have to concentrate on proper signaling when a call comes to the phone.  Does the phone ring at all?

The procedure to answer a call is this:
1) bell rings

2) take handset off-hook

3) push the button. This should cause proper ring trip. Ringing stops.

4) Here is comes the crucial point of failure with the documented circuit. When the pushbutton is released, the DC current loop is interrupted again and this means to the exchange that the user has hung up the telephone and the set is on-hook.  We must provide a way to maintain loop current by providing an impedance of ~600 Ω to the exchange. This impedance is also necessary locally in the phone, because we don't want to short out the receiver circuit.  We cannot remove the capacitor (1µF) in the receiver circuit because it must protect the receiver from direct current.

5) A normal call should at this point be established.  You have already tested this part of the call and reported that it works.

6) The telephone call is ended by hanging up the handset.  This must disconnect the impedance that we provided in step 4, so that the exchange sees a permanent loop disconnect.

So, let's start thinking about how to achieve steps 4 and 6.

unbeldi

Quote from: jhutzler on November 09, 2014, 11:40:34 AM
Ok Guys... thanks so much for your helpful advice.

I feel very humble to admit the white wire on the hookswitch was not on C1 as it should have been but instead was wired to C2. When I rewired ... presto, I have dial tone.

I have disconnected the Magneto as recommended and currently one side of the cap is not in use... the yellow and slate leads.

Minor problem... the ringer rings once everytime I lift the handset off the cradle (hookswitch).  I've read that isolating the reciever from the DC would help but isn't this already the case with my phone if I'm reading the schematic right.

Cheers  ...  Jeff

Ok, glad to hear that wiring is corrected.
Disconnecting the magneto is ok as it has no purpose, but not strictly necessary anymore with our current state of knowledge.

The single bell tap that you get when you take the receiver off-hook is expected actually.  The B1N ringer is unbiased, meaning its armature is free to move to either side.  So whenever the capacitor charge changes, a current flows through the ringer causing it to hit one of the gongs. Unbiased ringers were not uncommon on magneto lines.
We can help this by providing a separate capacitor for the ringer, in fact isolating the ringer circuit completely from the receiver/audio circuit.

unbeldi

#21
As another side note, the arrangement of the key and generator in this telephone also permits simplex signaling.  In this mode both sides of the line to the exchange are shorted by the key when pushing the button. After and while the button is pushed, the user cranks the generator.  The generator circuit is completed to the exchange through the ground connection. This prevents other subscribers on the party line from being disturbed by unwanted ringing, because their telephone set is also shorted during signaling.

Of course normal grounded signaling in both directions, ringing from the exchange and cranking at the telephone, for the tip-party and the ring-party is possible simply by appropriate connections in the unit.  All other signaling for multiple parties has to be with coded ringing.

poplar1

Here is an excerpt from the Northern Electric T8 catalog (1955):

SETS, TELEPHONE, MAGNETO-Continued

Selective Central Office Signalling

By means of a Selective Central Office Signaling System
a large number of subscribers may be connected on one
line, and each subscriber may signal Central Office without
ringing the bells of the other parties on the line. This
arrangement is known as push-button ringing and may be
accomplished by one of two methods. Parties on the same
line are called by straight metallic code ringing; the push
button not being operated.

Grounded Ringing. By operating the push-button the
generator is connected between one side of the line and
ground for calls to central office. At the Central Office
the signal is connected between one side of the line and
ground so that when the subscriber cranks the generator
the signal at the Central Office will operate.


Simplex Ringing. The second method, insofar as the subscriber's
operation is concerned, is accomplished in a similar
manner. When operated, the push-button key connects one
terminal of the generator to ground and the other terminal
to both sides of the line, which provides two metallic conductors
for the signaling current to Central Office where
appropriate signal termination is provided.
Telephones arranged for Simplex Signaling under many
conditions, particularly where there is inductive interference
from power wires, provide a quiet circuit. They have a
further advantage when transposition work is being done
on the fine in that there is Jess liability of a subscriber's
station being accidentally left so that they cannot signal
Central Office.
"C'est pas une restauration, c'est une rénovation."--François Martin.

jhutzler

Hi Unbeldi,

Thanks again for your help. I have disconnected red/blue strip from ground and the push button no longer affects the line (no clicks or disconnects)

The old phone has a dial tone, answers calls (I cannot confirm disconnect as I am using a cell phone to test and I need to end the call from the cell phone even after hanging up).  But I'm really happy so far with this arrangement.

On another note: I recently bought a AE50 wall phone from ebay for $12 and when I won the bid, I found out the seller lived just down the street from me. What are the odds?

Anyway, I bought a pulse-tone converter and hooked it up and the phone didn't work... but this is a project for another day.

Cheers,  Jeff

dsk

 ;) Now, I need help. I have probably missed something in the thread 8)
As I reed the diagram line 2 are connected to C2 going trough the capacitor to C1 independent of position of hook switch (the other wire from line 2 should go to the generator via the key, but the generator are disconnected so this should not carry current at all! If that's right the capacitor are not good, and lets DC pass trough.

I really wonder were I fell off  :P   by my opinion this should not work. :o

dsk

unbeldi

Quote from: jhutzler on November 09, 2014, 12:54:51 PM
Hi Unbeldi,

Thanks again for your help. I have disconnected red/blue strip from ground and the push button no longer affects the line (no clicks or disconnects)

The old phone has a dial tone, answers calls (I cannot confirm disconnect as I am using a cell phone to test and I need to end the call from the cell phone even after hanging up).  But I'm really happy so far with this arrangement.

On another note: I recently bought a AE50 wall phone from ebay for $12 and when I won the bid, I found out the seller lived just down the street from me. What are the odds?

Anyway, I bought a pulse-tone converter and hooked it up and the phone didn't work... but this is a project for another day.

Cheers,  Jeff

This means, I think, the phone has been already modified, and you don't know by whom.
All I can say is, once again, draw out the connection of all parts as they are in the phone and compare to the diagrams.

If it works, it does not mean it works correctly. A common mistake people (collectors) make is permit DC to flow through the receiver.  This may eventually render the receiver unusable, because it may demagnetize the permanent magnet. In addition it causes poor audio performance, as the diaphragm is improperly attracted to the magnet.


unbeldi

Quote from: dsk on November 09, 2014, 01:57:34 PM
;) Now, I need help. I have probably missed something in the thread 8)
As I reed the diagram line 2 are connected to C2 going trough the capacitor to C1 independent of position of hook switch (the other wire from line 2 should go to the generator via the key, but the generator are disconnected so this should not carry current at all! If that's right the capacitor are not good, and lets DC pass trough.

I really wonder were I fell off  :P   by my opinion this should not work. :o

dsk

You are right that there is a problem, which I described in my call flow earlier under item 4).
So the set has been modified from the factory condition.

dsk

I will not disagree in the statement of DC ruins the receiver, but it will take pretty long time so it is no risk doing a little testing, but it is not ideal to have it that way. 
If the original capacitor, ore at least one of them works you may use it between C1 and C2 in my suggestion for modified circuit.  This circuit includes a capacitor in series with the receiver. Connecting tip to C1 and moving ringer from C1 to C2 (or L2). This will make the original capacitor work as ringer capacitor, and let the dc flow trough the coil, but not the receiver.
The resistor between A and C1 may be shorted to get a better anti sidetone function since you probably have a relatively short loop compaired with a looong rural line.

Similar circuits has been used in the old days.

dsk

jhutzler

Hi Dsk,

I was wondering since I'm not using the half of the cap with yellow and slate colored wires (currently on C), could I just wire them up in series with the receiver. Is there a polarity issue here ... which colored wire gets tied into the white receiver wire?

Cheers,

Jeff

unbeldi

#29
The capacitor that you are not using is actually more suitable for the ringer, while it is too small for the audio circuit, except to provide line balancing.
But before doing any of that, you should determine why your set works the way it does.  I believe you don't have to push the button to answer a call as it is. Please check how the used capacitor is actually wired.

Wiring another capacitor into the receiver circuit is not enough. You still need to provide the DC bypass to hold the loop.
The only correct way to do this, I believe, is to use a retardation coil.  The 307 telephone uses a 266A retardation coil for this purpose, but that may be hard to find. A good substitute might be a No. 46 induction coil with both windings wired in series. Only problem with that is the coil is probably too big to fit into the set.