Broadcast Electronics 3000 Series - Cue Circuitry Bias Control; Record Control and Tone Generator Board; Configurations

Following the FET, the program signal is coupled through the bias
trap
C35 (C38), L1 (L2) which prevents the high level bias from overloading
the record
amplifiers. The variable inductor permits tuning the bias trap
to the exact frequency of the bias oscillator. Following the bias trap, the
audio signal
is mixed with the bias supplied through R3 (R2) and R64 (R63).
The variable bias control permits adjusting the bias level for optimum re-
cording from the particular tape used.
To prevent bias from appearing on the program track of the record
head except in the record mode, the switching circuit Q8, Q6 (Q7) is con-
ducting
C28 (C29) shunt the bias to ground. The base of Q6 (Q7) is connected
through zener diode
CR3 (CR4) and R46 (R45) to +24 VDC to permit Q6 (Q7) to
conduct.
In the record mode the base of Q8 is drawn towards ground through
CR5 to the record logic. Transistor Q8 begins conducting to bring down the
base of
Q6 (Q7) to shut this device off and to restore the bias. When the
record
logic is not in the record mode, the base of Q8 is held high through R50
and R51 to keep Q8 turned off. The bias is again shunted as Q6 (Q7) is held
in conduction.
Transistor Q1 in conjunction with C7 and C6 provide noise de-
coupling
for +24 VDC supply for the record amplifiers.
4-17. CUE CIRCUITRY BIAS CONTROL
The audio signal for the cue track is supplied from the Record
Control and Tone Generator Board to terminal 19. The audio is coupled
through the bias.
trap (C37, L3, C40) as in the program circuitry. The audio
is mixed with the bias from R1, R62 and supplied to the cue track of the
record head.
As in the program circuitry switching transistors Q9 and Q10
are employed to shunt the bias except when cue tones are actually being re-
corded. When Q10 is conducting, the bias is shunted. When QlO is turned off
by Q9 drawing the base of Q10 low, the bias is supplied to the head.
Transistor Q9 is turned on by a positive voltage supplied to its
base through R52. This voltage is supplied by the cue bias switch control
on the Record Control Cue Generator Board when any of the cue generators are
running or
when the external cue record is activated.
4-18.
4-19.
RECORD CONTROL AND TONE GENERATOR BOARD
CONFIGURATIONS
The Record Control and Tone Generator Board installed in record
models incorporates the record logic flip-flop, the VU meter amplifier,
and the 1 kHz stop cue generator. In units equipped with the QI 150 Hz
and QII 8 kHz Q-Trips, the generators for these cue tones are also included.
The board is built in four different configurations depending on whether
monophonic or stereophonic and whether or not Q-Trips are installed. These
versions are shown in Section VI.
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