Remote Cutoff Pentode
VT-49 is the Military designation for the
39 / 44 tube.
The 39 / 44 VT-49 Vacuum tube is a glass type used as an
RF or IF amplifier in radio receivers, particularly those
The 39 / 44 / VT - 49 is a super-control pentode
recommended for use primarily as a radio-frequency
amplifier, intermediate-frequency amplifier and
superheterodyne first detector in automobile receivers
and in sets operated from DC power lines. It has a
heater-cathode which is designed for DC operation. This
feature together with that of general freedom from
microphonic and battery circuit disturbances makes the
39 / 44 / VT-49 well suited to mobile service and other
applications where complete DC operation is desirable.
It is very effective in reducing cross-modulation and
modulation-distortion over the usual range of signal
voltages without the use of antenna potentiometers or
auxiliary volume control switches. This super-control
characteristic makes the tube uniquely adaptable to RF
and IF stages of receivers employing automatic volume
The use of a suppressor is an important feature
of the 39 / 44 / VT-49 because it permits variation in
tube structure so as to obtain a high plate resistance
without impairing other desired characteristics. In
comparison with the usual type of screen grid tube
operated under similar conditiona, it has a much higher
plate resistance and a considerably increased range of
voltage swing. Furthermore, a high value of mutual
conductance is maintained.
The suppressor is connected inside the tube to the
cathode. During operation of the tube, the suppressor
eliminates the secondary emission effects which limit the
voltage swing permissible in the usual screen grid tube
at low plate voltage, that is, at a plate voltage
approximately equal to thc screen voltage. The
suppressor, therefore, makes possible the efficient
operation of this tube at a relatively low plate voltage.
This may greater than, equal to, or slightly less than
the recommended screen voltage.
Heater Voltage ............................. 6.3 DC V
Heater Current ................................ 0.3 A
Preferred Substitutes .............. 44, 39, VT-49.