TM 11-6625-539-15-2
to-revere current ratio is read directly on the BETA
diode is forward-biased and conducts heavily. Resis-
scale of the meter.
tors R9, R5, meter shunt R27, and the forward resist-
ance of the test device limit the current through
5-7. F.E.T. CAL Check
meter M1. CAL potentiometer R5 is adjusted to set
a. A schematic diagram of the circuit used to
the current through M1 to 100 ma which corresponds
calibrate the test set for field effect transistor
to a full-scale meter reading. After CAL potenti-
( F. E.T.) transconductance measurement is shown in
ometer R5 has been set to provide a full-scale reading,
the polarity switch is set to NPN REV as shown in
transistor; however, the same principle applies for a
B, figure 5-5. The circuit is essentially the same as
P-chnnnel F.E.T. transistor.
the circuit used to obtain the reference reading; the
b. The F.E.T. CAL position of the function switch
sets the signal level applied to the test device at 100
only change is the reversal of the applied voltage
millivolts (mv) as follows. The 1-kHz multivibrator
and reversal of the meter. The test device is now back-
applies a symmetrical square wave between the
biased and offers a high resistance. Circuit current is
source and the gate of the F.E.T. under test. A volt-
proportionally decreased because of the increased
age divider, consisting of resistors R18 and R17,
resistence of the test device, and consequently, meter
shunts the source gate junction of the test device; a
deflection is proportionally reduced. The forward-
portion of the 1-kHz square wave applied between
