TM 32-5835-005-14 & P
output characteristics of the signal
6-3. Record/Reproduce Electronics.
electronics: receiver input 0.5 to 5
a. Signal Amplifiers. The AN/UNH-17A
VRMS, microphone input 0.1 to 1.0 MVRMS
and headphone output 0.0 to 20 milli-
Recorder/Reproducer utilizes different
amplifiers for recording and repro-
watts.
duction (See Figure 6-8.) For signal-
b. Record Amplifier. (See Figure 6-8.)
to-noise ratio considerations, the
This discussion will be confined to
playback pre-amplifier, which handles
low level signals from the playback
channel 1. The RECORD mode is selected
by simultaneously pressing REPRO and
heads, is located near the tape trans-
port mechanism on a small plug-in mod-
RECORD switches (A1A2S1 and A1A2S3) on
ule A1A8. This amplifier boosts the
the front panel. Microphone and re-
playback signal to a high level for the
ceiver signals are mixed in the resis-
main data signal amplifier A1A3, which
tive network R43, R44, R45. The com-
is common to record and reproduce pro-
bined signal is applied to K1 and then
cesses. In the RECORD mode, signals
to the non-inverting input of amplifier
from the MIKE jacks A1J2 and A1J4 and
U1A. This amplifier in turn provides
the RCVR jacks A1J3 and A1J5 are resis-
an amplified signal to U2A and then to
tively mixed and connected to the in-
drivers Q1 and Q2. The frequency re-
put of the amplifier through relays K1
sponse of this circuit card is 200 Hz
and K2 on A1A3. The amplifier outputs
to 8 KHz. No high frequency boost
are connected to summing points on
occurs here; headphone monitoring is
undistorted by pre-emphasis. The am-
the bias oscillator board A1A4 for add-
plifier U1A is followed by the gain con-
ition to the bias signal.
trol circuit, manual or automatic. Both
6-9.) The bias oscillator is turned on
manual and automatic gain control is
during the RECORD mode to provide high
frequency bias required for low dis-
accomplished by resistive shunting of
tortion recording and the combined
the output of amplifier U1A, which is
data signals and bias signals are
provided by A1A2R2 (front panel) in
applied directly to the record head.
manual mode and by field effect tran-
sistor Q3 in AGC mode. A portion of
The HEADPHONE jack A1J1 is connected
the output of amplifier U2A is converted
to the bias oscillator board and can be
energized by either a record or repro-
to DC by a voltage doubling rectifier
duce signal. The headphones monitor
circuit; the error (feedback) signal
the data signal electronics during
thus developed across C17 is applied to
RECORD/REPRODUCE and STOP. In RECORD,
the gate of field effect transistor Q3.
the pre-emphasis necessary does not
The magnitude of resistance presented
by Q3 is controlled by the voltage on
affect headphone response as the pre-
its gate and the position of AGC pot-
equalization occurs after the headphone
jack. The channel selector permits
entiometer R16. Resistive shunting in
headphone monitoring of channel 1
the AGC feedback loop varies in direct
and/or channel 2. Switching for
proportion to changes in the output
equalizers is achieved with solid
signal level. This arrangement permits
state analog switches. Switching
the output level to remain constant
for channel selection and record/
within 3dB with changes in input level
repro functions is achieved with
as great as 15dB. The amplifier output
miniature relays. During RECORD,
from Q1 and Q2 is applied to the bias
high level, high frequency sig-
oscillator board A1A4 through K3. (See
nals to the record heads would ex-
Figure 6-9.) At TP3 a 50 KHz sine wave
is added to the amplified data signal.
ceed the breakdown voltage rating of
analog switch devices. The relays
Q3 is connected in a Hartley oscillator
handle high peak-to-peak currents and
configuration. The combined audio and
also improve crosstalk in playback
bias signals are supplied to the record
mode. Following are the nominal input/
head via relay K1 on the pre-amplifier
Change 1
6-11
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