Type 51 Ericsson

[unbeldi]

Extension sets were not supposed to be connected simply in parallel with the main telephone set on the line.
For extension sets, all these PTT types had an extra connection terminal EW (Extra Wekker) which was switched so that the extension was also offline during off-hook conditions.  So, if properly done, there was no chance of bell tap.

The ringer impedance is also too low in these sets for connecting more than one ringing bridge across the line simultaneously.  They had to be switched in series to reduce the load.

[Matilo Telephones]

The EW connection is specifically for an Extra Ringer. Extra Wekker means Extra Ringer. It was supposed to be connected in series with the ringer so both would ring at the same time and be disconnected at the same time, when te Phone went off hook.

What you are describing is an extra feature called a tweeling schakeling, twin connection whereby the 2nd telephone on the line was switched off line, by picking up the handset on the first and vice versa. I am not sure this is possible with all Norm 51 telephones. It is a standard feature on the T65 though.

About that ringer on the T51: on the back of the clapper are 2 screws. Tightening them will stiffen the ringer mechanism, making it less sensetive to pulses on the line.

[unbeldi]

The EW connection is specifically for an Extra Ringer. Extra Wekker means Extra Ringer. It was supposed to be connected in series with the ringer so both would ring at the same time and be disconnected at the same time, when te Phone went off hook.

What you are describing is an extra feature called a tweeling schakeling, twin connection whereby the 2nd telephone on the line was switched off line, by picking up the handset on the first and vice versa. I am not sure this is possible with all Norm 51 telephones. It is a standard feature on the T65 though.

About that ringer on the T51: on the back of the clapper are 2 screws. Tightening them will stiffen the ringer mechanism, making it less sensetive to pulses on the line.

Exactly.  It means 'twin circuit' in translation.
I don't think I have seen a PTT diagram of that era without the feature. It is in the 1951, 1952, 1955 types, and later T65 types.

[AL_as_needed]

About that ringer on the T51: on the back of the clapper are 2 screws. Tightening them will stiffen the ringer mechanism, making it less sensetive to pulses on the line.

I figured the ringer would have some form of adjustment in it. I will check later and make some tweaks to it.

Extension sets were not supposed to be connected simply in parallel with the main telephone set on the line.
For extension sets, all these PTT types had an extra connection terminal EW (Extra Wekker) which was switched so that the extension was also offline during off-hook conditions.  So, if properly done, there was no chance of bell tap.

Would this be the equivalent to the exclusion feature on WE sets?

[AL_as_needed]

I took a look at the ringer in the T-51 and it does not seem to have an adujment screw. Of the three screws related to the clapper, they all hold it in the ringer itself. What I thought was the adjustment was actually holding the clapper it place.

[unbeldi]

Indeed, I didn't think so.

We have to realize that the telephone networks of yesterday were not designed or capable of just plugging things together without thought or plan in any manner as desired in every situation.
This is only possible with today's telephones that have low-load electronic ringers without grounding. Some telephones today have a REN of 0.1 or lower !  A Western Electric 500 set has REN 1.0, and these Dutch or other European telephones of that time can be measured at REN 2 or higher.

Wiring only two of these up on the same line, as intended using the exclusion feature, is the correct way, and makes a worthwhile display of not only the elegance of these sets (IMHO), but also their technical features of the 1950s.

[AL_as_needed]

It's interesting to see how different companies tackled similar issues when looking at the U.S. and EU phones from the same era. Ma Bell and the PPT system clearly had different goals and priorities when designing their systems and equipment. Not saying any one is better than the other, just a different philosophy was applied.

Someday when I have a PBX I'll sort this sort of bug out, for now it's a testament to the individuality of the design. 

[Matilo Telephones]

I took a look at the ringer in the T-51 and it does not seem to have an adujment screw. Of the three screws related to the clapper, they all hold it in the ringer itself. What I thought was the adjustment was actually holding the clapper it place.

I took a look at the ringer in the T-51 and it does not seem to have an adujment screw. Of the three screws related to the clapper, they all hold it in the ringer itself. What I thought was the adjustment was actually holding the clapper it place.

At the front of the ringer there are 3 screws. 2 for fastening it to the base plate. The other one is for adjusting the length/swing of the clapper. Loosening it, lets you move it back or forwards.

At the back of the clapper there are 2 screws, see picture. Tightening them, bends the pivot (axle?) a little, making it less flexible.

[unbeldi]

At the front of the ringer there are 3 screws. 2 for fastening it to the base plate. The other one is for adjusting the length/swing of the clapper. Loosening it, lets you move it back or forwards.

At the back of the clapper there are 2 screws, see picture. Tightening them, bends the pivot (axle?) a little, making it less flexible.

But that would be to adjust the resonance of the ringer, not a bias.

[AL_as_needed]

At the front of the ringer there are 3 screws. 2 for fastening it to the base plate. The other one is for adjusting the length/swing of the clapper. Loosening it, lets you move it back or forwards.

At the back of the clapper there are 2 screws, see picture. Tightening them, bends the pivot (axle?) a little, making it less flexible.

I tried the various combinations of screw tightness and position and it seems the options are ring or no ring  . This ringer is far more sensitive than that found in WE sets that I am used to. For now I'm putting any ring issues the T-51 may have on hold (all but two phones are getting boxed, moving). In the future i may try and add a bias spring to the ringer, or re-wire everything via a PBX to avoid the issue altogether.