Siemens & Halske identification (and repair?)

[olli]

Hello, and thank you for the access to the forums.

I found this old Siemens & Halske rotary phone at a flea market. Would it be possible to get some help on:

1. Identifying it. The front plate would seem to say ZBSA 19E, but I couldn't find any similar looking phones using this as a search term. Closest was maybe this BTMC 2650: http://www.matilo.eu/the-phones/before-1926-metal-and-wood/btmc-2650/

2. Issue with the ringer. I've connected this phone to a Grandstream HT-802 ATA, and it otherwise works, but the ringer wont either make any sound at all, or there will only be a very small vibration. I've set the high power ring option on in the HT-802, but it doesn't change the situation. I've heard ATA's might have trouble with these phones, is there anything that can be done, or could it be some other issue?

3. On the handset, there is a button that can be pressed, but it doesn't seem to do anything. The previous owner might have made some modifications too. What is the purpose of this button, and can I possibly restore it?

Also any other comments and info about the phone, refurbishing it etc are also appreciated. I have a multimeter and other sorted basic tools, but have never tried to restore something like this.

[olli]

Additional images.

[countryman]

It is in fact a ZBSA 19 wall phone:
https://radio-bastler.de/forum/showthread.php?tid=18696

The metal handset was replaced with a later model 38 type, with a push to talk button like on a field phone.

The ringer should be made for 25 Hz, but is not a tuned frequency ringer. It should work well enough from 15 to 50 Hz. Possibly it has lost it's permanent magnetism, or the capacitor is bad. More likely it just does not move completely free (is dampened mechanically). Intensive cleaning of the pivoting points may help. Use oil very sparingly, if any. The link above mentioned serious ringer issues from zinc rot, I hope this is not the case here!
The phone looks very nice and well kept, congratulations on the find!

Edit, the dial is a model 21, quite rare in that nice condition!

[olli]

Thank you for the information and the link. The link showed an example of cracks in the ringer parts, which seems to be happening in this phone as well, I've attached a picture of that. So maybe it's at least partially responsible for the situation.

The phone did manage to ring a little bit in some situations, so maybe it's not hopeless. I'll definitely try to do some cleaning next.

[countryman]

Oh, that does not look very good. Be very careful with the cracked part, it might crumble to pieces. Zinc rot is a huge problem, it comes from an inferior composition of the alloy and is not reversible. The problem was not known by the time the phone was made. I have heard the recommendation to stabilize the cracks with epoxy compounds. Not sure if that would help here? You might try to adjust the setting screws in the next step to free up the clapper. Good luck!
The phone enthusiast in the linked thread ended up copying the part from scratch (last picture in the link)

[TelePlay]

That looks like a frequency ringer, right?

=====

Anyone have experience using near water thin UV curable glue?

I haven't but was wondering if it would work on zinc rot to hold the cracks together and also encapsulate the deteriorating part.

Being thin, it should seep into the cracks and wet the surface holding everything together after being cured with the included UV pen light.

This is one of many examples found on eBay, prices vary:

https://www.ebay.com/itm/256148475971

My dentist uses this to cement crowns in place, must be water proof.

[dsk]

Nice phone, pretty rare dial too. The ringer is may be working even with the cracks, It has a spring to let it rest in one position, I would have tried to loosen that tension and see if it moves easily. If yes, it is a good sign. The 2 750 ohms windings have a center point between them that makes one of the coils shunt the transmitter element. Check out if the hook-switch separates all 3 cords in on hook position. The ringer current travels trough the the capacitor and a strap between terminals marked W2.
Not sure what you have of tools, but if you have a multi-meter the resistance between a and W2 terminals should be around 1500 ohms in on hook position.  The capacitor should be between b and W2 and should be around 1 uF. I f you have no capacity metering the ohm meter should react by a value and no value while changing the polarity on the cords. (Still on hook position)
The wall plug seems equal to what we used to have here in Norway, but they were commonly used in Finland and Italy to the end of the digitalizing of the phone systems.  The ringers should work well both on 20 and 25 hz. (As countryman stated, not sensitive to frequencies.) The ringing current was generated with simple circuits and could probably be quite different from the nominal 25Hz, I have measured one exchange with as little as 13 Hz, and the last PABX's from Ericsson used mains frequency.)
Many phones did not ring well at more than 30 Hz.

[olli]

Some observations, see attached picture

- The ringer (in green) moves relatively freely left to right. But there is no tendency to stay in any one particular position. So if I understood correctly that there should be a spring somewhere here to give it tension, I'm not noticing it.
- The little notch (in red) doesn't really seem to make contact with the ringer. Should it?
- The cracked part (in yellow) has some flakes coming off the surface, but otherwise it feels at least somewhat solid. It might not be in as bad of a condition as in the link mentioned by countryman.
- The hook-switch does separate the three terminals in on hook position. Off-hook the terminals are all connected.

The electrical resistance between a and w2 terminals are:
~1430 ohms off hook
~1570 ohms on hook

I'll have to return to the issue of capacitance measurements later.

[dsk]

The measured resistance look perfect! If the green par moves freely it is a good sign. The spring is there to reduce tinkling while dialing, and should not be of importance before the end of the project that makes you feel the need of fine tuning of minor details.
Not easy to see of the pictures but the green mechanism should have the screw on top in a center hole to make it move freely and stable. (Edit: That hole seems to be slightly to the right of the center on these ringers.) When you barely touch it it should move as much as it touches the gongs, but do not rest against the gongs. The magnetism from the permanent magnet should be strong enough to feel it with a screwdriver held close to the magnet. If the magnet has been weakened it may actually be stronger again when the ringer is in regular use. (Just an observation, I not may explain why.)  If you use 2  9v batteries in series and touches w2 and A with that voltage, the gongs should be hit each time you change the polarity of the connection, then the ringer is OK.  I have had several German capacitors that was not good any more. If so: I have solved that by taking out whats inside and soldered in a new capacitor in the metal box.  Carefully flip out the metal fingers holding the front, let the capacitor rest in hot water for some minutes, and the tar inside becomes soft, and you may slide it out.  (Edit: The part that holds the ringer seems to be a weak point on the linked thread too, so be careful.)

PS
The handset looks equal to the ones used on the WWii field telephone FF-33
DS

[olli]

- Applying 18 volts across the w2 and a terminals, then switching polarity doesn't seem to do much. Sometimes I can see the smallest of twitches in the ringer, and sometimes nothing. Would this indicate that the capacitors have gone bad?

- I've attached a picture of the ringer when it's moved as far as it can in one of the directions. I wonder if it's somehow allowed to move even too far? As you can see the screw coming from the top is nowhere near the small hole that is in the top of the ringer.

- The permanent magnets still attract the tip of a screwdriver, but the effect is pretty weak. You sometimes almost have to try multiple times to be sure it's there.

- Looking again at the cracked block, there does seem to be pretty bad damage, not just on the surface. If the part is only structural, and doesn't have to for example conduct electricity or be magnetic, maybe I could try to 3D print a replacement? I have no idea whether anyone has spare parts such as these available.

Thank you for all the assistance so far! 

[countryman]

The clapper should be pivoting on the tip of the screw (toe bearing). The way it is, the ringer motor is out of alignment and may not work properly. 
Zinc rot is a bad issue, the parts are swelling and cracking from inside out. If you could stabilize the part with glue (UV curable or epoxy...), and the screw could be turned without breaking the part, it might be possible to realign the clapper. I hope I got all the subjunctive forms right... in other words, I see a slim possibility 
The part is only mechanical, not electrical. 3D printed from the right material, it should work fine. I'm not sure whether the screw threads are metric or still a special "Siemens Telegraph" thread?

I found a more clearly drawn schematic in Günther Mergelsberg's book "Das Telefon und seine Entwicklung":

[TelePlay]

The clapper should be pivoting on the tip of the screw (toe bearing). The way it is, the ringer motor is out of alignment and may not work properly.

Missed that, thanks for explaining. It looked like a frequency ringer until I saw the pivot point out of its mounting point.

The problem is with the point not being held into the pivot hole (yellow line inside the yellow circle), right?

And looking at the mount up close, that zinc rot looks to be beyond repair, needs replacement.

3D printing using a metal filament should work, but having the proper printer and programming the printer's code would be a challenge. That's about all I know with respect to 3D printing.

[countryman]

Here's my own personal zinc rot nightmare. The part crumbled to pieces soon after I photographed it. 
The phone (a "Priteg" line selector) already had one of both line switches replaced with a steel part, which I then copied by bending and cutting/filing sheet metal. Perhaps that could also be an option here? The poster in the other forum filed it out of solid metal blocks...

[dsk]

If you look at the thread : https://radio-bastler.de/forum/showthread.php?tid=18696 the same part was 3D-printed, so it is done before.

I would probably have tried the glue solution, but you may make a replacement of whatever you have, and it does not have to look equal as long as it works as the original one to hold the hammer stable and swing freely, and that it keeps the magnet working.  What is North or South pole of the magnet is not of importance, but both the cores of the coils has to be one pole, and the other has to be close to the hings of the clapper (hammer mechanism).

I f you just replace the ringer mechanism with a different Siemens ringer you may need to adjust the resistance of the center tapped wire to be at least 500 ohms including the resistance of on of the coils, but that will depend of the transmitter capsule used (microphone).

[countryman]

... and that it keeps the magnet working. 

Good point. If made of steel, the part might "short circuit" the magnetism. I suppose the poster in the other forum filed it out of aluminium?