Dropping resistors
These were mainly used in France and Belgium to be able to use 110-130 volts AC/DC receivers at higher voltages. In French these adaptors were called "Bouchons dévolteurs" or "Résistances chutrices".
They were made for various voltages and wattages. The most common voltages are 220V -> 110v and 130v -> 110v.
The left resistor is a type YO50, 550 ohms, 50 W, made by the Belgian company ADB (Adrien DeBacker), a company founded in 1920, still active in lighting sytems for airports. The middle one is a French resistance, suitable for 25 W; The right one is also French and - although physically larger - suitable for 20 W.
These resistors have several drawbacks. They use a lot of power and can become very hot. Moreover, they sometimes contain asbestos and they do not fit into a rim-earthed power socket.
It is important to chose the correct resistor. The output voltage depends on the power required by the connected radio. If the radio consumes more power than indicated on the resistance, it gets less than 110 volts and if it uses less power, the device gets more than 110 volts and that could be dangerous.
These resistors were used mainly in the 50s and 60s of the last century.
French advertisement for a number of dropping resistors.

This page was last edited on 15.07.2017