ZB / SA 24
The table instrument ZB / SA 24 ( Z entral b atterie operating / S ven a onnection operation, Model 24 ) was one of Siemens & Halske developed and in 1924 under the name "W 24" by the German Post or the Empire Telegraph Administration (RTV) Telephone set in use as a standard set . "W xx" was the term used in 1924 by the post office for W ählapparat. The previous model was the visually similar, somewhat larger ZB / SA 19 , which was introduced shortly after the First World War .
General
The designation "ZB / SA" means that the device obtained the power for its carbon microphone from a central battery via the telephone network ; In contrast to the local battery (OB) devices, there was no longer any need for a battery at the subscriber or for cranking to generate the call voltage . Thanks to the number switch with finger hole disc, the device was suitable for self-dialing, i.e. for automatic call switching, and was therefore a self-dialing device.
The participant only had to dial the phone number and was automatically connected to the person he wanted to talk to, as is still the case in principle. At that time, self-dialing was only possible in the local network . Long-distance connections still had to be switched manually. The expansion of the self-dialing network in Germany took a long time due to economic crises and wars. The last hand-operated local exchange in the Federal Republic of Germany was taken out of service in 1966 .
Appearance
The design of the ZB / SA 24 is quite angular and not as ergonomic as the successor models. Special features: an almost cube-shaped housing cover made of black painted sheet steel - bevelled at the front, a nickel-plated brass finger-hole disc ("number switch 24" or "N24"), the sweeping, curved nickel-plated earpiece , the handle- shaped, also nickel-plated handset with flat, circular Earpiece and spherical or funnel-shaped microphone entry point ("handset 24"). In contrast to its predecessor ZB / SA 19, the two bells of the alarm clock are no longer on the back of the case, but rather on the inside. A special key is required to open the housing. All components are mounted on the sheet steel base plate and freely wired with bound cable harnesses. The number switch can be folded down for repair purposes. The finger disc is blocked when the handset is in place. This was necessary in terms of the circuitry and, as a side effect, forced the "correct telephoning" (pick up the handset, wait for the dial tone, dial the number).
successor
The device was produced in large numbers, but at that time a telephone was a luxury item that only public institutions, business people or well-to-do groups could afford - hardly a private household. Already in 1928 , four years after its introduction, the ZB / SA 24 was replaced by the technically improved and optically completely redesigned, much more successful model W 28 . This was already much more widespread.
The ZB / SA 24 is now a collector's item. Well-preserved specimens are rare, the devices are mostly in need of restoration. You can still use it to make calls today, provided that the connection or the telephone system can use the traditional pulse dialing method (IWV); otherwise a converter is required. However, the voice and audio quality of the old remote receivers / carbon microphones left a lot to be desired.