The UY-237 was low mu triode, originally designed for use in car radios. Manufactured by: Ken-Rad Corp. Owensboro, KY, USA.
Used as a class A amplifier, It has a 6.3 volt indirectly heated cathode.

6.3 volts was chosen as a suitable voltage for use in car radios intended to be operated from a 6 volt car battery, standard in the United States in the 1930s. The reason for this choice of voltage was that 6.3 plus 10% is about 7 volts, the voltage seen when the car's engine is running and the battery is fully charged and 6.3 minus 10% is about 5.7 volts, the voltage of a 6 volt battery at about 20% state of charge. This means that over the expected range of voltages to be experienced, the heaters will stay within 10% of their rated voltage, the normally accepted permissible range for valve heaters.
This heater voltage was then rapidly accepted as the default standard for all indirectly heated valves in the United States.

Physical Description

Conical glass bulb with no top cap on American style 5 pin (UY) base.

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