Planar Triode
The G.E. ~ General Electric 2C40 Vacuum tube is a historic
planar triode tube of lighthouse construction designed
with an octal base that was developed to operate at UHF
frequencies for use as an
oscillator or radio-frequency amplifier at frequencies
as high as 3370 MHz. The radio-frequency cathode
connection is made through a disk-type capacitor which
is incorporated in the tube. This results in a
low-impedance radio-frequency path from the cathode to
the external circuit. The envelope construction results
in low losses, provides convenient electrode contact
surfaces and enables the tube to fit easily into
coaxial circuits. Conventional vacuum tubes could not operate
above 100 MHz because their interelectrode capacitance
and lead inductance were too great. These planar triodes,
commonly referred to as "Lighthouse Tubes" because of
their unique appearance, were constructed quite
differently from other vacuum tubes. The heater and
cathode were in the base. The grid was one level above
the cathode with connections being made by the metal
ring at that level. The plate was in the top section of
the tube. These were used for the first time during
World War II. It requires an octal socket.
Electrical Data:
Heater Voltage ............................. 6.3 V
Heater Current ............................ 0.75 A
Preferred Substitutes ......................... 4037