Siemens W48 repair

[Alcedo]

Hello!
I'm trying to repair a Siemens W48 (at least that's what I think it is, based on the groundplate and production year 1957).
I would like it to work on our telephone line. I searched on the internet and this forum, and now I know that it will probably only work with incoming calls.
Now, I hooked it up to our net (I live in Belgium), and it rung, I answered it, and didn't hear anything, and also the person on the other line couldn' hear anything. Then I discovered there was no microphone or speaker installed! 
So I searched a bit, and used a small speaker and microphone that fit inside the horn.
Next, tried it again, and now I can send and receive messages via the phone, but it's very silent (both on my line and the other line).

So I thought a while, and now I have 2 hypotheses:
- speaker and microphone aren't suitable
- the net uses smaller voltages then it used to (I think this is more probable)

then, I thought if there may be a resistor used for amplification. So the next plan is to replace this resistor. So I searched a lot for wiring diagrams of the W48. I found many, but none of them represent the scheme I see in the telephone (see pictures). First thought: it's only a different language (mine is probably in french or dutch language). Closer examination made me doubt this.
As you can see, I thought a lot about it, but being a beginner with old telephones, I'm stuck.

So my questions are:
Am I searching for the wrong model? Or is the wiring scheme equivalent? If so, what resistor or capacitor do I have to change to change the amplification, or are the speaker and mic not suitable?

Kind regards from Belgium,
Roeland

[Matilo Telephones]

Hello Roeland,

The phone you have is indeed a W48. But the year of production does is not a 100% indication of it's type. The modell 36 was made in Bruxelles well into the 50s.

It's the strip with connection screws over the bells and the ways the wires run out of the back that makes it a W48 (and some other details).

It should work normally on your telephone line, if properly connected.

Where did you find the microphone (transmitter) and speaker (receiver)? Can you post pics of them here?

[unbeldi]

It looks like a W48 mT, but is it really made by Siemens?  Is there a logo?
The lettering in red ink on the bottom does not look to me like it was done by Siemens, or it was not made for the German Bundespost.  Such devices usually have very neat stamping in silver-gray ink and include the Siemens manufacturing code which expresses the date and location of manufacture, so for the year 1957 it should be something like "11 N 12".

The finger wheel face is also unusual. In which country were letters used in Europe in the 1950s?

There are two additional components inside, capacitors it seems, and do seem to detect the outline of the Siemens logo on the large one (left).  Are these somehow connected with the earthing button?

[Matilo Telephones]

I had a Siemens W38 in for repairs. It had the same red lettering and dating on the bottom. And the same lettering on the dail.

That phone was also from Belgium, where Roeland and his phone are located.

Also I have a modell 36 made in the 50ies by Siemens Bruxelles. It has the same red lettering, but no date.

I think this phone was made by Siemens Bruxelles too. Especially because it has a diagram in French and Dutch, which indicates Belgium.

Also I see a small blue round stamp with the Flemish lion on the speaking coil and the capacitor. That is typical for Belgian phones that were not in the RTT inventory (Belgian state phone company), in my experience.

[Matilo Telephones]

Oh, hang on. The coding on the bottom is the same as the one I had in for repairs.

The only difference between a W38 and W48 is the coding and the housing does not fit completely over the baseplate.

That last distinction was not visible in the pictures.

The W48 housing fits flush with its baseplate. On the W38 the base plate sticks out about half its thickness.

But as the coding is the same as the one I had, that would make this a W38 and not a W48.

Some versions of the W38 have even more differences with regards to the W48. But the later versions are almost identical to the w48.

[unbeldi]

So I suspect these were all made for private customers, for connection to a PABX.

[Matilo Telephones]

I think so too. Not for the RTT or Deutsch Post anyway.

[unbeldi]

I think so too. Not for the RTT or Deutsch Post anyway.

Companies with international business often had to place calls to, for example, the United States, where until the early 1960s most subscribers still had 2L-5N  telephone numbers with exchange names, and the lettering on the dial increased the productivity of workers or of secretaries quite a bit, I would imagine.

Could they have had direct international dialing back then, lol?   Doesn't seem right thought.

[dsk]

Back to the original question, The receiver and transmitter capsules used on these are so equal that you will have trouble to know when they are mixed or right.  I would say if it fits like it is made for the handset its, probably right.  The receiver should have a dc resistance of approx 40 ohms, but I have "seen" it working well with a 120 ohms receiver too.
Regarding the transmitter, this are more sensitive, it should work at a voltage of less than 2 volts. Almost no transistorized replacement capsule copes with that, but some do.
Carbon capsules are safer. Some door telephone systems uses pretty good capsules, STR, Siedle and others, some of these are polarity sensitive.

If you put the receiver, transmitter and a 4.5 V battery in series, you should here pretty loud what you say.

dsk

[Matilo Telephones]

The way Roeland describes how he obtained a microphone and speaker makes me wonder if they are telephone parts at all and if they are correct for use on a normal telephone line.

If they are the correct parts it would be quite a coincidence that they both have aged to such an extent they they are weak.

Switching the A and B wire sometimes improves sound quality quite a bit.

[Matilo Telephones]

Oh dear, I think we scared Roeland off, now.

[Alcedo]

Hello I'm back! Sorry for my absence but I had exams, so no spare time.
The housing does not overlap with its baseplate. Also, there are Siemens Bruxelles logos on the housing.

The transmitter and receiver are parts that I found in other (modern) electronic devices, and probably not suited. The resistance of the transmitter is too low, 8ohms. The transmitter comes from a microphone (OK now it's confusing  - a microphone with a TRS 6.35mm connector, used in music).
Are there places where I can buy/find a new or used receiver and transmitter for a decent price?

Thank you!

[dsk]

Good to hear that we did not scare you away

About any old telephone used compatible units, even door telephones. The closest you come the receiver in modern things may be in a lo cost headset having a loudspeaker of at least 30 ohms. (just for testing) or maybe if the transmitter you have may work as a receiver element?

The transmitter (microphone) used was actually a small box with carbon more or less compressed by the movement of a membrane, this caused a variable resistance on level you today need transistors to make from your microphone.

dsk

[Matilo Telephones]

Hi Roeland,

I have these for you if you like. I live in Leiden, Holland. So not very far away.

PM if you are interested.

On Ebay there are some sellers who sell them. Most of them in Germany. Search for W48 ersatzteile.

[dsk]

Problems with transmitter may be tested out in many ways.  A 9 v battery http://tinyurl.com/p3xuo9m do usually have high internal resistance, and you may just connect the phone to it and test if you hear yourselves loud and clear.

dsk