Advertisement
SECTION
II
BC- 250GY
-1
TRANSMITTER DET
^AILS
The following information on the BC -250GY
transmitter pertains
to the
general construction and operational detail surrounding
the transmitter itself.
As
in all
modern transmitting equipment
it is
best
to
look
at
the
transmitter
in its
various sections
as
pertaining
to
overall performance detail.
Oscillator Unit
The
oscillator unit
is
located on the inside left
of
the cabinet,
facing the back, directly below the 813 intermediate amplifier
stage.
This is the
standard Gates M -5422 Oscillator Unit, using
vacuum
crystals.
It
can be readily removed by loosening the four
mounting
screws, and
unplugging
the
connecting cable.
The operation of the M -5422 oscillator unit
is
explained in detail
in
a
separate section
of
this instruction book.
The
filament
and
plate supply
are
obtained from
a
power supply on the audio driver
chassis;
a
part
of
this supply also
is
used for the modulator bias
voltage.
A voltage divider delivers approximately 150 volts
to
the
M
-5422 oscillator unit, and with this voltage the unit
delivers
ample power
to
drive the following 813 stage.
The 813 stage
is
equipped with
a
grid current meter
M8,
mounted
on the 813 chassis.
The
M
-5422 oscillator unit, which
is
oper-
ating when the filaments
are on,
can be tuned according
to
in-
structions for the maximum grid current reading on
the
meter
M8.
This will be approximately
8
-
10
milliamperes without voltage
on
the plate of the 813.
The
vacuum crystals have
zero
temperature
characteristics,
and are
operable on frequency
as
soon
as
the
tubes heat
to
normal emission.
Any delay in setting the fre-
quency will be due
to the
requirements
of the
frequency monitor
having
to
reach
a
stable heat level.
There are no gaps to set.
The
crystals
are
normally received from
the
supplier after having
been calibrated
in
a
M -5422 oscillator unit, and before shipment
are
retested
in the M -5422
oscillator unit supplied with the
transmitter.
It
can be
anticipated that the frequency will
be
within
a
very few cycles
of the
specified frequency, within
the
range
of
adjustment
of
the frequency trimmer condensers.
9/11/63
-2-
BC-250GY-1
Advertisement
