GPO Bellset 26 on Canadian/US network

[Ktownphoneco]

As Jack has suggested, double check that single coil's impedance.      When you did the initial measurement, was the coil fully isolated from the circuit ?

Jeff

[Fennec]

Attached is a modified version of the schematic you posted.    Try connecting your central office line as indicated.    It shows the line connection change suggested by Unbeldi, and eliminates the resistor Jack referred to as the "half hearted" attempt to convert the ringer to a high impedance version.      If you haven't already checked, it might be a good idea to remove the 2 machine screws holding the circuit board in place, and carefully lift and twist it slightly, in order to verify that the empty terminals and jumpers shown on the schematic, are in fact, arranged as indicated. 
Even if it doesn't vibrate itself off the table, at least you'll know the ringer itself is functioning to some degree.

Jeff Lamb

OK, tried as per diagram (this path still takes the signal through the 2 uF capacitor), connecting RED to B4, and GREEN to B8. Striker deflects hard to the right, being pulled in by the 500 Ohm coil. This is where is stays, no oscillation to other coil (with suspect resistance). If left in this condition, the landline becomes "off hook" or "busy".

Does this mean that 2nd coil is bad? Should I try shunting it with a ~840 Ohm resistor to bring the value to ~500 Ohm? Or these are symptoms of something else?

[Jack Ryan]

OK, tried as per diagram (this path still takes the signal through the 2 uF capacitor), connecting RED to B4, and GREEN to B8. Striker deflects hard to the right, being pulled in by the 500 Ohm coil. This is where is stays, no oscillation to other coil (with suspect resistance). If left in this condition, the landline becomes "off hook" or "busy".

What happens if you reverse the line connections? Does the clapper go to the other side?

Do you have a spare capacitor you can use in place of the one in the bellset?

Does this mean that 2nd coil is bad? Should I try shunting it with a ~840 Ohm resistor to bring the value to ~500 Ohm? Or these are symptoms of something else?

A shunt won't fix it - just mask it. Try reversing the line and then using another capacitor first.

Jack

[TelePlay]

A shunt won't fix it - just mask it. Try reversing the line and then using another capacitor first.

Yes, the each coil is that part of the ringer, the two electromagnets, that pulls the clapper from side to side with AC voltage. Some have rewound the coil. Others have opened the coil to find the break, or in this case a partial break,  by unwinding the coil, fix the break and rewind the coil. Some just find a new ringer. All depends on what you find, how much to want to spend, how much time you want to spend and your interest in "fixing" something. Some of the stuff I've tried to fix end up in the trash can and then I go looking for a "new" old part, if you know what I mean. Tinkering can be fun, at times, if it works out well.

Here's one member's experience with finding and fixing a break. Some ringers, such as a B1A out of a 302 can lose part or all of the permanent magnet field when removing the coils (another topic on the forum). Not sure if you ringer would have that problem.

[Fennec]

What happens if you reverse the line connections? Does the clapper go to the other side?

Reversed connections - yes, the clapper goes to the other side. Again - it just stays there, no oscillation. Come to think of it - is there supposed to be an oscillation? In absence of ringing signal, I think there is only DC voltage present on the line, no AC...

I have not changed the capacitor yet, but I have a few modern polyester ones I can substitute...

I think I will try to revert back to original N526 schematic, as you have suggested, i.e. remove the resistor, and connect RED to B2 and GREEN to B8... I am not sure if it is the resistor that causes entire house line go "busy" when connected per Bob Freshwater's schematic...

[Jack Ryan]

Reversed connections - yes, the clapper goes to the other side. Again - it just stays there, no oscillation. Come to think of it - is there supposed to be an oscillation? In absence of ringing signal, I think there is only DC voltage present on the line, no AC...

I have not changed the capacitor yet, but I have a few modern polyester ones I can substitute...

I think I will try to revert back to original N526 schematic, as you have suggested, i.e. remove the resistor, and connect RED to B2 and GREEN to B8... I am not sure if it is the resistor that causes entire house line go "busy" when connected per Bob Freshwater's schematic...

It looks like the bell mechanism is working, despite the abnormal resistance. Let's ignore the abnormal resistance - at least for the time being.

Next problem is that connecting the bell with capacitor in series seizes the line - the capacitor seems to be emulating a conductor (it's broken).

Find a replacement, even a modern equivalent, capacitor - replace the original capacitor and I suspect that the bell will ring. Return the circuit to that shown in the N diagrams and you should be good to go.

Later on you might find that you are limited in the number of phones you can use in parallel and still have the bells ring. Worry about that later.

Jack

[dsk]

It seems to be something to straighten out before I my advice's becomes useful.
1)The subset is made for UK, pre central capacitor was introduced.
2)The size of the 2 uF capacitor is normal for the time and place.
3)The ringing load at setup will be far more than 1 REN (US standard)  UK ringing usually was about 25Hz at 90V
4)The original ringer had 2 500 ohms coils. Usually configured to form a total resistance of 1000 ohms (dc) but sometimes used in parallel forming a 250 ohms resistance.

Not easy to determine why the high ohms reading on one coil. A visible inspection and re metering may determine if it is a bad winding, or bad soldering.

The encl diagram is your original with white moved to include capacitor. 
For testing please try it with 1: a strap between terminals 1 and 6.
and 2: if not 1 works. remove the strap 1-6 and strap 9 to 6.

Regards
dsk

[Fennec]

OK, thank you everybody for your help so far. I would like to report a success (almost)! I have decided that since coils and capacitor are suspect anyway, to give entire bellset a mild solvent bath. Washed thoroughly with water after 10 min soaking, and left for a day in the hot sun (+34C/93F in the shade) to dry.

Strangely enough, left coil measures now 512 Ω, right - 501 Ω (??) Didn't touch anything, just cleaning and slight wiggle of connecting wires to check soldering...

RED wire connected to B5/B4, GREEN wire connected to B7/B8 (resistor removed) - all per N4300 and diagrams drawn by Jack Ryan and dsk.

Good: Connected this way, the house phone is acting normal again. Bellset rings on dial (Yesss!)
Bad: There is an audible single "tinkle" of the bell when taking any handset in the house off hook, and another one after replacing it back on hook.

I also have to note that connecting to B9 through a 3.3 kΩ resistor between B9 and B8 works too, although it does not address "tinkle" issue. Is this resistor needed for anything in this case? Connecting red (BT white) wire to B2 as I have originally drawn does not work - the phone line becomes off-hook.

With this in mind - are there any steps I can take to address the "tinkle" before I move to phase two, i.e. interconnecting the bellset and the phone proper?

[Jack Ryan]

Congratulations!

The resistor is meant to increase the impedance of the bellset so that connecting it to the line does not load the line and stop other phones from ringing. If the bell rings properly with the resistor in circuit then you can leave it there. The rest of the circuit should be as per the N diagrams, not Bob Freshwater's WEB site.

I assume that the bell is no longer seizing the line.

The ding you hear is a feature, not a fault. You might try reversing L1 and L2 and/or adjusting the gong being tapped a bit further away. If the tapping continues and you want it stopped it can be addressed but that is phase 2. First get the phone connected and working.

The usual GPO fix for bell tapping was to use a thermistor in series with the bell. Have a look at the circuit of a Tele 312 as a guide (no need for a diode across the thermistor).

http://www.samhallas.co.uk/repository/n_diagrams/0000/N412.pdf

Regards
Jack

[dsk]

Great!
To Jack: Do you have any suggestion for what thermistor to order to do the job (substitute the one in Tele 312)?
I have used a circuit similar to this: http://tinyurl.com/35rq874   but I used a quadrac (triac without need of diac).
The hence, and result of using the circuit was to increase modem speed.
I have used the spring from a pen to make a bias spring and that works well to stop bell tinkle.

dsk

[dsk]

Thank you for this thread   

I just saw a little green drop with 2 legs laying on the floor today, lost by some tech person, and it happened to be a thermistor, probably for using in the ventilation system. 

I tried it in series with a ringer, and so far it seems to do the job.  The unit happend to be the last one on the list on this picture.

Now, I have putted it in to a SC 1243 with a to weak bias spring, this phone used to tinkle. (I turned the adjustment screw for the spring so it does not do anything)  It seems to do the job.

dsk

[unbeldi]

You seem to be confusing the terms thermistor and varistor.   You are showing a table for varistors.

A thermistor is a resistor whose resistance varies with temperature.
A varistor is a resistor whose resistance varies with the current flowing through the device.

Potentially both could be used for the task, but they have to have just the right specs.

The idea for suppressing bell tinkle is that it is a very transient event with very little energy that can easily be dissipated in the device.  Bell tinkle is a very short lived pulse generated from the two current slopes on either side of interruption of current.  It contains high frequencies which cause self-induction in the ringer windings.
So, to suppress them the resistors has to have very high resistance, likely hundreds of kilo-ohms when cold.  Small amounts of energy wouldn't cause a rise in temperature and therefore the tinkle is quenched.   During ringing, the thermistor needs to warm up sufficiently so that its resistance drops dramatically to a few tens or hundreds of ohms so that it doesn't dissipate and waste too much energy.    So, the response curve of these must be very steep.

With a varistor, the current flowing through the device during ringing has to drop the resistance in similar manner from very high to very low.
The response curve of a varistor is also dependent on temperature, btw.

[Jack Ryan]

To Jack: Do you have any suggestion for what thermistor to order to do the job (substitute the one in Tele 312)?

I see there was a question to me that I missed - sorry about that Dsk.

I have not found the specs for the GPO Thermistor 1A but I have been told the cold resistance is 100k. (I don't have a Thermistor 1A to play with).

I have tried various 100k (and other) NTC thermistors but none will heat up enough with the initial cold current to cause the thermistor to "conduct". The result is the bell never rings (but there is no tinkle). So I do not have a modern equivalent.

What does work, albeit with a small reduction in ring energy, is a series resistor of about 4k7 (actual value not overly critical). Together with the bell capacitor, this forms an RC filter with a time constant sufficient to filter out the pulses that cause tinkle. The "conversion resistor" of 3k3 would also work.

I'm not sure how effective a varistor would be - I would have thought it would stop ringing all together or have no effect, depending how it was connected and its specs.

Jack

[dsk]

You seem to be confusing the terms thermistor and varistor.   You are showing a table for varistors.

A thermistor is a resistor whose resistance varies with temperature.
A varistor is a resistor whose resistance varies with the current flowing through the device.

Potentially both could be used for the task, but they have to have just the right specs.

The idea for suppressing bell tinkle is that it is a very transient event with very little energy that can easily be dissipated in the device.  Bell tinkle is a very short lived pulse generated from the two current slopes on either side of interruption of current.  It contains high frequencies which cause self-induction in the ringer windings.
So, to suppress them the resistors has to have very high resistance, likely hundreds of kilo-ohms when cold.  Small amounts of energy wouldn't cause a rise in temperature and therefore the tinkle is quenched.   During ringing, the thermistor needs to warm up sufficiently so that its resistance drops dramatically to a few tens or hundreds of ohms so that it doesn't dissipate and waste too much energy.    So, the response curve of these must be very steep.

With a varistor, the current flowing through the device during ringing has to drop the resistance in similar manner from very high to very low.
The response curve of a varistor is also dependent on temperature, btw.

You are right ... again 

We have to find the right ntc to replace the one used in UK.

By the way, when I did put in the varistor rated 39V do I lower the ringing voltage with 39 V all the time, or do I just cut of the part of the sinus curve between +/- 39V but getting full power the rest of the half wave?



dsk

[dsk]

Since it is about impossible to find anything about this, I have started some experimenting.  My first investment: http://tinyurl.com/j6lo5xw

Thermistor Temperature Sensor Ntc Mf52-103 3435 10K Ohm 5%

10 K is about the impedance of a ringer with capacitor of 1REN (7K) and would probably drop to far less. I have trouble measuring this instantaneous values, but an old ringer 1K + 1 microFarad known for tinkling it works when dialing, but I get a ding when polarity changes on the line. On my line it happens when we go off/on hook.

dsk