Advertisement
In regard to loudspeakers, however, a few points
should be emphasized. Facilities are provided for two
speakers. A third speaker may be added by addition
of accessory speaker relay kit MI-11748. The loud-
speaker should have a voice CQil impedance of 15
ohms, or an impedance matching transformer MI-
11731 must be provided.
As to warning lights, the MI
-11
706
Series are
recommended for the Studio and Control Room. The
lights which are available with inscription, are listed
as follows:
ON AIR
REHEARSAL
AUDITION
STANDBY
SILENCE
MI-11706-1
MI-11706-2
MI-1l706-3
MI-1l706-4
MI-11706-5
An MI-11702-A Warning Light Relay is recom-
mended for each warning
light.
Circuit Description
The BC-3C Consolette amplifiers are constructed
on individual etched circuit boards. External connec-
tions are made through turret type terminals on each
board. The boards are secured with standard hard-
ware to a metal chassis and are easily loosened or
removed to gain access to the etched wiring.
Figure 3-Preamplifier (SAR J-SAR3J Printed
Circuit
Soard
\
5
Preamplifiers SAR 1 to SAR3
The circuit of the microphone preamplifiers is
shown in the schematic diagram of figure 5. The
input signal is derived from an unloaded step-up
transformer which is mounted under the preamplifier
mounting shelf and is applied to the grid of the
input stage. This stage is RC coupled to the second
stage, with negative feedback from the plate of the
second stage applied to the cathode of the input stage.
This minimizes distortion at high input levels. A
MI-1l299 tube which is a 12A Y7 selected for low
noise is used in this stage. The output of the second
stage is connected through the coupling capacitor tC2
to a potentiometer type MIXER gain control and
hence to the grid of the third stage. The output of
this stage is capacitively coupled to the cathode fol-
lower output stage. A 12A Y7 tube is used here. To
eliminate any doc output voltage which could produce
switching clicks, two capacitors IC5 and lC6 are
connected in series between the cathode and the out-
put terminal with shunt resistors lR12 and IR13
bleeding l\ny charge to ground. The voltage gain of
the amplifier is approximately 46 db. An input signal
to the transformer primary of -50dbm produces an
output signal of approximately one volt.
Figure 4-Preamplifier (SAR4, SARSJ Printed
Circuit
Soard
Advertisement
