Author Topic: W28 (German)  (Read 1818 times)

Offline dsk

  • **
  • Posts: 4089
W28 (German)
« on: March 10, 2013, 08:54:06 AM »
This circuit may be drawn differently, I have tried to redraw after Ralp Meyers book translate.
Please comment.
dsk
« Last Edit: November 11, 2013, 12:36:05 PM by dsk »

Offline dsk

  • **
  • Posts: 4089
Re: W28 German)
« Reply #1 on: March 11, 2013, 11:04:31 AM »
A picture of my telephone:

(The transmitter cap is not the right one, it should look more like a ball)

dsk

Offline countryman

  • *
  • Posts: 456
Re: W28 (German)
« Reply #2 on: June 05, 2020, 08:39:41 AM »
The above diagram is normal for a Modell 26 and W28.
The original Modell 26 designed by Siemens & Halske had sound slots on the base. This is a very rare version! It was never approved for official use but was restricted to private systems.
The W28 then was officially approved and made in large numbers by Siemens and many others.
Simultaneously, private versions were still made that more resemble the Modell 26, but without the sounding slots in the base. Yours seems to be such a phone, usually referred to as "Modell 28". Frequent differences compared with "official" W28 are:
-Handset cord enters the shell on the back
-metal cradle and upper part of shell
-nickel finger wheel
-card holder is not a separate part screwed to the front, but an oval window right in the shell.
These are often stamped VSatist66.. on the bottom.

Electrically, all these versions are alike, or so I thought until I came across this diagram with the addition "Na.v-Nachbildung veränderlich": https://www.youtube.com/watch?v=XjGmFMzX6JM&list=LLRI5YE17geu5JArErr8a9nw&index=3&t=0s 1:44 min.
Unusual for German phones of that time it optionally uses a second capacitor for the anti-sidetone circuit in parallel with a 600 Ohm resistor. Normally a 200 Ohm resistor alone is used (400 Ohm on later German models).
The phone in the video seems to be a W28 made by Stöcker & Co., Leipzig. Unfortunately, the youtuber does not show the underside.

The low DC resistance in parallel with the transmitter (200+95 Ohm) is the culprit for the low microphone voltage available on these phones. Transistor capsules will often fail on them, as well as aged carbon mics that still work fair on other phones.
« Last Edit: June 05, 2020, 08:57:15 AM by countryman »

Offline RB

  • **
  • Posts: 1314
  • Love old phones
Re: W28 (German)
« Reply #3 on: June 05, 2020, 09:41:24 AM »
DSK, if that top pic is your drawing, it is Infinitely better than the scan pic!!!
were you a school teacher in a past life? ;)
I can read that top pic. Thank you!

Offline dsk

  • **
  • Posts: 4089
Re: W28 (German)
« Reply #4 on: June 06, 2020, 05:09:46 AM »
DSK, if that top pic is your drawing, it is Infinitely better than the scan pic!!!
were you a school teacher in a past life? ;)
I can read that top pic. Thank you!


Regarding the german phones changig that 200 or 400 ohms resistor to a resistor in series with a capacitor of 1-5 uF you will get a slightly different side tone damping, but a transmitter will get all the DC current and that will make it easier to put in a transmitter from e.g. a WE 2500.
or a transistorized capsule. 

dsk
Thank you, it was a test to try to translate the way of drawing schematics.

Yes I'm a teacher, and will probably continue with that for a few years more.
The last 3 moths has been a little different where teaching has been digitalized and the lessons has been Teams meetings. Now it seems to slowly turn back to somthing closer to the traditional school. We have leearned a lot and the school system is hopefully developping to a better school than before.

dsk