c. remains constant regardless of amplifier loading.
d. increases the amplifier's gain by adding to the input voltage.
9. A large paper cone is connected to the voice coil of a dynamic loudspeaker to
a. minimize mechanical resonance.
b. cancel out harmonic distortion of the ac waveform.
c. reproduce high and low frequencies with equal efficiency.
d. efficiently radiate sound waves by pushing large amounts of air.
10. Four types of loudspeakers are shown in figures 203 and 204, TM 11-665.
The
loudspeaker that does NOT use a permanent magnet is shown in
a. A of figure 203.
c. A of figure 204.
b. B of figure 203.
d. B of figure 204.
11. Assume that an output transformer in a push-pull electron-tube amplifier must
be replaced because of failure. This transformer has been used to match the plate-
to-plate impedance of 5,000 ohms to a voice coil impedance of 8 ohms.
The
replacement transformer should have a turns ratio of approximately
a. 15 to 1.
c. 625 to 1.
b. 25 to 1.
d. 900 to 1.
12. In the power amplifier circuit shown in B of figure 205, TM 11-665, the
plates are connected in series through the primary of the output transformer. The
primary is center tapped to permit feeding equal dc plate voltages to the tubes.
There must be enough turns in the primary winding so that
a. each half of the winding matches the plate-load impedance of one tube.
b. there is a direct impedance match between the primary and secondary.
c. two output signals, 180 out of phase, may be taken simultaneously.
d. two output signals of equal amplitude may be taken simultaneously.
13. In the transistor AF preamplifier shown in figure 4-1 of the attached
memorandum, degenerative voltage is taken from coil L2 in the output rather than
from resistor R3 in the input because
a. the voltage in L2 is in phase with the voltage in R3.
b. there is normally less dc voltage drop across L2 than across R3.
c. coil L2 couples the degenerative voltage into the following stage.
d. degeneration cannot cancel out distortion before distortion occurs.
322 L4
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