Fun project with the kids - need guidance

[Ohliuw]

I think the crank phones have some special wiring needs.

I did a test with a candlestick phone and a subset ringer, which doesn't have the magneto mechanism. When I have only this phone connected to the switch, it works as follows - lift the receiver=start ringing; put down the receiver=stops ringing. This is the video I made:

Now, when I add a magneto phone, the situation changes. In the next video I connect one of the magneto phones in addition to the candlestick. If I lift the candlestick phone receiver - it rings; however, when I put it down - it doesn't stop ringing. The only way to stop the ringing is to do a very short crank.

on the magneto phone, when I do short crank, the port opens and ot doesn't continue ringing after. However, when I crank hard and long the magneto phone, the switch keeps ringing even after I stop cranking. The only way to make it stop ringing is to do a very short crank. Here is the video

Any thoughts?

[Ohliuw]

Did some testing with a volt meter, and I know what the problem is - just don't know how to fix it.

Mode 1. When the 12v power supply to the switch is turned on, on each extension port (e1 to e8) there is a reading of 12v.
  1a) when I connect the subset ringer to one of the ports (the one without the magneto), the meter still reads 12v on that port. The moment I lift the receiver, the voltage drops to 2v and the switch ringer starts ringing. When I put the the receiver down in place, the meter reads again 12v and it stops ringing.
  1b) when I connect a magneto phone, the meter reads less than 12v in that port - different crank phone gave different readings - between 7.5 and 9.9v. I tried connecting 3v,6v, 9v and even 12v power supply to the crank phones where the batteries were connected - it didn't change the reading. The voltage drop remained constant. So something the magneto phones causes the voltage drop.


Now it appears that a sudden drop  in voltage activated toe ringer. once the switch ringer is activated, it waits for all ports  to read back to 12v before it stops ringing. Obviously this doesn't happen on the magneto phone ports. Thus a short crank helps as the voltage spikes past 12v.

Mode 2. In this scenario, I did not connect the 12v to the switch.
  2a) obviously lifting up and down the receiver on the subset ringer didn't do anything - there was nothing to power it. The ports read 0V at all times
  2b) when magneto phones are connected, the ports read 0V as expected. When I crank them, it makes the switch ringer to ring. When I stop cranking, it doesn't ring, which is the desired behaviour BUT when I crank one phone, in addition to the switch ringer, all other phones attached to the extension ports are ALSO ringing.

So in Mode1 (12v connected to the switch), I need to figure out how to prevent the voltage drop caused by the magneto phones

In Mode2 (12v NOT connected to the switch), I need to prevent the ringing on the other connected phones.

I am fine in either mode!

HELP!

[poplar1]

If this is a common battery switchboard (lift the handset or receiver to signal the attendant), then you should not be connecting magneto telephones as extensions, or, at least, not sending ring voltage from the stations (extensions) to the attendant.

Magneto phones can only be connected to the trunk (outside line) ports.

[Ohliuw]

If this is a common battery switchboard (lift the handset or receiver to signal the attendant), then you should not be connecting magneto telephones as extensions, or, at least, not sending ring voltage from the stations (extensions) to the attendant.

Magneto phones can only be connected to the trunk (outside line) ports.

Thanks!!! any explanation why? Also, is it possible to rewire the magneto phones to use them as extensions?

[tubaman]

If this is a common battery switchboard (lift the handset or receiver to signal the attendant), then you should not be connecting magneto telephones as extensions, or, at least, not sending ring voltage from the stations (extensions) to the attendant.

Magneto phones can only be connected to the trunk (outside line) ports.

Now I'm confused as I agree that you shouldn't send ringing voltage from a magneto on a CB system but then why would it be ok to have magneto phones on the outside line ports?

[poplar1]

Thanks!!! any explanation why? Also, is it possible to rewire the magneto phones to use them as extensions?

Local Battery phones (magneto) can be used if you add a capacitor in series with the ringer and disconnect the hand generator (magneto). You would still need the 3 Volt (2 cells) or 4.5 V (3 cells) battery for the transmitter, unless you swap out the induction coil and rewire the phone, which is more trouble.

If a ringer does not have a capacitor in series on a POTS line (traditional line), it may busy out the line to incoming calls, or trip the line on the first ring then busy it out, because it looks like an off-hook condition to the central office.

[poplar1]

Now I'm confused as I agree that you shouldn't send ringing voltage from a magneto on a CB system but then why would it be ok to have magneto phones on the outside line ports?

Because a local battery phone (with magneto), like an incoming trunk (outside line), provides its own talk battery and ringing current to signal the switchboard.

[countryman]

It should be possible to use regular dial phones as extensions on this switchboard, just the dials have no function.
As poplar1 said the LB (magneto) phones might be rewired to CB, but it's a bit elaborate.
12V might work as a supply for the switchboard, but normally at least 24V were used.

[Ohliuw]

It should be possible to use regular dial phones as extensions on this switchboard, just the dials have no function.
As poplar1 said the LB (magneto) phones might be rewired to CB, but it's a bit elaborate.
12V might work as a supply for the switchboard, but normally at least 24V were used.

I found the PDF here that shows how to make a PCB or how to rewire (less desirable).

This would work http://www.classicrotaryphones.com/forum/index.php?topic=4361.0

[tubaman]

Because a local battery phone (with magneto), like an incoming trunk (outside line), provides its own talk battery and ringing current to signal the switchboard.

I see what you are saying - I was thinking that the outside lines were connected to real live lines, which of course they are not.

[countryman]

I found the PDF here that shows how to make a PCB or how to rewire (less desirable).

This would work http://www.classicrotaryphones.com/forum/index.php?topic=4361.0

The link to further information given in the other thread is dead, unfortunately. But the site is still available on the internet archive:
http://web.archive.org/web/20170920072659/www.oldphoneguy.com/
I added this to the other thread as well.

[Ohliuw]

The link to further information given in the other thread is dead, unfortunately. But the site is still available on the internet archive:
http://web.archive.org/web/20170920072659/www.oldphoneguy.com/
I added this to the other thread as well.

There is a PDF attachment at the first post, which is what I am hoping to ise to build the boards.

[Ohliuw]

Ok, before we go crazy on building PCBs, there should be an easier way.

If I Look at the ringer substation, which works fine with the switch - there is nothing special- in fact it has the same components as my Northern Electrics, except the NE has the magneto mechanism. So if I disconnect the magneto, it should be possible to rewire it to work with the switch:

The ringer substation:


The crank phone:


Thoughts?

[Ohliuw]

Figured it out. No PCB is needed.

My goal is to have the switch ringing when the receiver is off the hook and stop the ringing when put down.

The magneto will be only ringing the local ringer (this is still to be worked on, I am planning to use a relay, for now it's just disconnected ).

The ringer will be ringing when the switch magneto is cranked.

There are 2 scenarios - for those with external headsets, it's straightforward. what's needed to cross connect the headset wires. We are looking to close the loop when the receiver is off the hook, and open when on the hook. In addition,
If condenser is not present, a capacitor for the finger is needed.

With built-in receiver/transmitter and local batteries, some soldering is needed to achieve a circuit similar to the one in the first case (the local battery needs to be eliminated and the power for the receiver must be drawn from the switch)

Any ideas on what relay I can use for the magneto and ringer?