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4
i
CIRCUIT DESCRIPTION
DC DETECTION
The relay is released when DC voltage appears at the out-
put terminals.
Thus the loudspeaker system can be protect-
ed.
When positive (+} potential is generated at the output
terminals, Qe19
is turned on to turn off Qe21
and Qe22,
and
the
relay
is released.
When
negative
(—) potential
appears at the output terminals, Qe18 is turned on to turn
on
Qe20.
This causes
Oe21
and Qe22 to turn off, and
the relay to be released.
MUTING
OPERATION
FOR AM
+Vcc
Relay
AM
signal line
Signal
short-
circuited
to GND)
Transistor
Qg6
composes
an AM
muting circuit.
When
the selector switch, Sg1, is set in the FM position, +14 V is
applied to the anode of Dg3. Then voltage is applied to.the
base of Qg6 to turn it on.
The AM signal is transferred to
the GND circuit and the tuner output cannot be fed to the
preamplifier.
In the AM
position, voltage to the base is
applied from the —50 V and Og 6 is turned off. The signal
is then fed to the preamplifier.
When
the power switch,
S1, is turned off while the selector switch is in the AM
position, there may be a signal leakage.
To avoid it, the AM signal is transferred to the GND circuit
simultaneously when the power switch is turned off. When
the power switch is off, the relay driving transistor Qe21
is also off and the collector potential is raised as a result.
This potential is applied to the base of Qg6 through Rg82,
and the AM
signal is led to the GND
circuit as described
previously.
MUTING
OPERATION
FOR
FM
+14V during
+18V
the FM position
| +B for the FM
| front end circuit
I and
ICg3
\Cg1
Rg78
No. 12
terminal
Dgs
12 (switch)
Y
\cg3
Qg
'
No. 10
ICg3
terminal
No. 11
terminal
Qg8 | Qg9
|0g10]
Qg12 (switch)
short-circuit
During tuning
During detuning
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