Some common power devices are the power MOSFET, power diode, thyristor, and IGBT. Some sources define silicon-controlled rectifier (SCR) and thyristor as synonymous. Its formal name is bidirectional triode thyristor or bilateral triode thyristor. Modern servomechanisms use solid state power amplifiers, usually built from MOSFET or thyristor devices. A thyristor is not a proportional device like a transistor. The name "silicon controlled rectifier" is General Electric's trade name for a type of thyristor. It is from a combination of "thyratron" and "transistor" that the term "thyristor" is derived. The term "thyristor" was derived from a combination of "thyratron" and "transistor". There is thyristor chopper control of the DC motors. Freon cooling for thyristor converters has been provided. The wafer device is similar to a gate turn-off thyristor (GTO). This supplies a single gate current pulse that turns the thyristor onto its on state. In 1973 the T603 became the first Czechoslovak car with contactless thyristor ignition. The latter is known as a gate turn-off thyristor, or GTO thyristor. It is equivalent to a thyristor with a disconnected gate.