Subscriber pay phone 55b
As a subscriber coin-operated telephone 55b (Tln Mü 55b), the then German telephone network operator Deutsche Bundespost called a telephone with a coin slot , which from the mid-1950s was the successor to the similarly designed coin-operated telephone 33 (TiMü 33) and a forerunner of the so-called " Club phones " was used. It was a coin-operated telephone that was designed as a table-top device and was mainly set up in restaurants , pensions or club houses , i.e. in semi-public places. In contrast to the normal public telephones in telephone booths, the supervision and emptying of the coin compartment was not the responsibility of the Federal Post Office, but the owner, who kept the money and settled it with the monthly telephone bill. From a legal point of view, this was not a public telephone and could therefore not be marked as such.
The device was available in black. Telephone receiver , fork and finger hole disk (rotary dial) are similar to the W48 telephone . A special feature is the elongated metal housing in which a coin slot and a lockable coin drawer are integrated. A label with a short instruction manual (see photo) is attached to the top of the housing. Colloquially, the Tln Mü 55b got the nickname "Groschengrab".
Tln Mü 55b was only permitted for local calls. The caller had to have two ten- pfennig coins ready and put them on top of each other on a slot. If a connection was established after dialing, the coins had to be inserted, only then was the microphone activated and you could speak. The coins fell into a small drawer on the front of the device. This very simple method had the disadvantage that possible incorrect connections (in which the user, if he noticed the called party when reporting that he was wrongly connected, did not insert the coins, but interrupted the connection) at the expense of the connection owner (in the official German at that time " Affiliate ") left.
A sophisticated, very complex mechanism of the number switch prevented long-distance or international calls by checking the dialed number sequence and blocking the connection if necessary ( restricted number switch ). When dialing, a three-armed lever and contact mechanism was set in motion, which successively checked the first three digits. This type of number switch was also used with the public coin-operated telephones and could be configured by setting appropriate solder bridges in order to prevent chargeable connections to manual international switching or services such as telex or telegram recording.
In order to prevent blocked numbers from being dialed by briefly hitting the fork ("fork selection"), this was slowed down by a small air pump. The built-in locks could be bypassed with a second, special key, so that the subscriber could use the Tln Mü 55b like a conventional telephone.
Insiders could easily bypass this complex ban. The Post itself was to blame for the regulation that every connection had to have a wall socket with a disconnecting plug that could be opened without tools. Before the conversation, a disconnect plug was pulled and any number was dialed, just not the zero. This lifted the lock. Then contact was re-established and long-distance calls could be made for any length of time.
Since clocking for local calls was only introduced in the mid-1970s, you could make unlimited calls with this device for 20 pfennigs. The introduction of this timing was also the reason for the closure of Tln Mü 55b. This device is very popular with collectors today; however, copies with a complete set of keys are rarely available.
- Handheld dictionary of electrical telecommunications ; Published on behalf of the Federal Ministry for Post and Telecommunications; Revised edition, Volume 2 G – P, (coin operated telephone); Bundesdruckerei Berlin, 1970; Pp. 1149-1154