TM 11-6625-539-14-3
b. The F. E. T. CAL position of the function
level applied to the test device can be accurately
switch sets the signal level applied to the test
set at 100 mv by adjustment of CAL potentio-
device at 100 millivolts (rev) as follows. The 1-
meter R5 while observing the meter for a full-
kHz multivibrator applies a symmetrical square
scale reading.
wave between the source and the gate of the
5-8. F. E. T. READ Check
F. E. T. under test. Voltage divider R18 and R17
GM measurements of field effect transistors are
shunts the source gate junction of the test de-
accomplished by the test set in the following
vice; a portion of the 1-kHz square wave applied
manner. The 1-kHz multivibrator, when properly
between the source and the gate is picked off
calibrated by adjustment of CAL potentiometer
at the junction of R17 and R18 and is applied to
R5, applies a symmetrical 100-mv square wave
the input of audio amplifier Q4, Q5, and Q6. The
between the source and gate of the test device.
output of the audio amplifier is rectified by bridge
Operating voltages are also applied to the test
CR1, CR2, CR3, and CR4 and is applied to the
device. The 1-kHz square wave appearing at the
meter. A full-scale meter reading indicates that
drain of the test device is applied to the input of
the square wave applied to the F. E. T. is 100
the audio amplifier. T h e output of the audio
mv in amplitude. The output level of the multi-
amplifier is rectified by bridge CR1, CR2, CR3,
vibrator (input level to the test device) is varied
and CR4 and is applied to the meter. The meter
by adjusting CAL potentiometer R5. The signal
is calibrated directly in GM micromhos.
