duced by the ac grid signal voltage. Meter M3
S19 is closed). During the first half-cycle of the
indicates the plate current changes caused by
input voltage when plate No. 1 of tube V1 is
applied grid voltage changes, or the mutual
positive, the ac signal voltage also swings the
grid of the tube under test to a positive poten-
f. During operation, PERCENT QUALITY
tial. The plate current is increased and more
meter M3, shunt resistors R40 and R42, and
current flows through resistor R40 and poten-
potentiometer R44 are switched into the circuit
tiometer R44. As a result, the deflection on the
by operating FUNCTION switch S4 to the
scale of meter M3 is greater than in the absence
T E S T position and depressing PRESS TO
of the signal voltage. During the next half-cycle
TEST P4 switch S19. PRESS TO TEST P4
when plate No. 2 of tube V1 is positive, the sig-
nal voltage will swing the instantaneous voltage
switch S19 applies plate and screen voltages to
at the grid of the tube under test to a negative
the tube under test. Ac signal voltages are ap-
plied to the grid of the tube by the front of GM-
potential. The plate current is decreased and less
current flows through resistor R42 and poten-
SIGNAL RANGE switch S5, while the rear of
switch S5 connects the proper multiplier resis-
tiometer R44. Consequently, the deflection of
meter M3 is now in the opposite direction and is
t o r s in series with quality SHUNT poten-
less than in the absence of the ac signal voltage.
tiometer R33 for each signal voltage range.
During each succeeding half-cycle, the current
When in position F, switch S5 removes signal
is now opposite and unequal, and the meter
voltage from the tube under test to permit zero
reading will be proportional to the difference in
adjustment of meter M3 by GM CENTERING
current between two half-cycles. The same un-
potentiometer R44. (In position F, no signal
balance in current exists during each succeeding
voltage is applied, but SIGNAL meter M4 still
will deflect. ) Various values of either cathode or
cycle and thus, over a period of time, the meter
reading will be proportional to the average value
fixed bias can be applied to the grid of the tube
of the difference in instantaneous currents pro-
under test by bias range switch S2.
Figure 5.
T r a n s c o n d u c t a n c e measurement circuit of Test Set, Electron Tube
TV-2(*)/U.
(Located in back of manual)
Tube TV-2(*)/U is shown in figure 6. The cir-
6. Emission Measuring Circuit
cuit is a simple series circuit with the tube under
test, and the meter circuit serves as a load for
a. An emission test performed on rectifier
the applied ac voltages. One-half of the high-
tubes and diode sections of multielement tubes
voltage plate supply of power transformer T2
will indicate whether the tube can provide a
provides ac test voltages from taps 3, 6, and 7
sufficient number of electrons for satisfactory
(3, 6, 7, and 8 on TV2C/U). These voltages
operation under normal service. The emission or
are selected by the settings of PLATE-SCREEN
saturation current of a two-element tube can be
RANGE switch S3 through section 1. Current-
measured if all electrons emitted by the cathode
limiting resistors R19 through R25, connected in
are drawn to the plate. Emission falls off as a
series with the tube under test, limit the total
tube wears out, therefore, low emission is indica-
current to a safe value. The total current in the
tive of the end of the normal life of a tube. The
"circuit is determined by the series-limiting re-
test for emission is limited, because it does not
sistors selected, the resistance of the tube under
test the tube under normal operating conditions,
test, and the resistance of the meter circuit.
but only for static voltages. Residual gas cur-
Because the tube under test rectifies the current,
rent, nonuniform cathodes, and other faults
PERCENT QUALITY meter M3 is used to
may supply normal emission current when the
measure the emission. Quality SHUNT poten-
tube actually is in an unsatisfactory condition.
tiometer R33, connected across meter M3, per-
Some tubes will operate satisfactorily after
mits adjustment of meter sensitivity and limits
emission has dropped far below the original or
the total current. Meter multiplier resistors R30
rated value.
and R31 can be connected in series with meter
b. A simplified schematic diagram of the emis-
sion measuring circuit of Test Set, Electron
M3 through GM-SIGNAL RANGE switch S5.
10
AGO 1428A
