Medium-Mu Triode
The 7A4 Vacuum tube is a glass lock-in type used as a
detector, amplifier, or oscillator in radio equipment.
It requires lock-in socket.
The 7A4 tube was used extensively in Hallicrafters Radios
such as the model SX42 radio manufactured between 1947
and 1949.
Electrical Data:
Voltage ................................ 6.3 V
Heater Current ......................... 0.3 A
Preferred Substitutes ................... 7B4, XXL