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In some
instances
of
unusual loading conditions, particularly
very low impedance antennas, the value
of
tank padding conden-
ser
C33,
may be affected
as
applied
to
normal charts and
if the
amplifier will not resonate with
the
load applied,
it
would be
the antenna and would only be in case
of
direct coupling, infor-
mation
as to
the
antenna or loading characteristics should be
immediately supplied
to the
factory.
Audio Chassis
The audio chassis
is the
hinged chassis
on the right
hand
of the
cabinet facing the rear and accommodates the push -pull 6L6G (1622)
Class A audio driver, the
push
-pull Class B 810
modulator tubes
on the top of the chassis and also accommodates the
combination
oscillator -bias supply
and its associates 5Ú4G tube and the
vacuum type time delay relay
E6.
The output of the 810
modulator
tubes terminates
to
modulation transformer
T3,
located in the
bottom
of the
cabinet.
The plate voltage to the
6L6G tubes
is
approximately
375 volts.
The
modulator tubes operate
at
the full
plate voltage
of the
main power
supply.
For under- chassis servicing
of the audio deck, it is
only neces-
sary
to
remove the knurled thumb screws and this chassis hinges
back revealing
all
under- chassis wiring
and
components for fast
servicing where required.
It
should be noted that
the
oscillator
bias power supply
is so
constructed that 60 volts
is
taken from
the
negative side
of
this supply
to
provide bias voltage for
the
modulators, which
is
individually adjustable by bias resistors
R4 and
R5.
Relays
The thermal operating filament time delay relay is
mounted
on the
audio chassis; the control element
being connected across
the
filaments
of the
6L6G tubes.
In case of
breakage
of the time
delay relay by accident or failure,
to
resume
operation
a
temporary expedient can be had by removing
the
time delay tube
from the audio chassis and placing
a
jumper between terminals
67 and 68.
In this
way there
is no
time delay action and the
overloads may trip from
a
cold start.
This
is
usually
due
to
the
bias voltage not having obtained full value.
By waiting
a
few seconds after the initial start no trouble will be encountered
Using
the
transmitter without
the time
delay
tube, of course,
is
not
recommended and the above
is
mentioned only
for servicing and
emergency procedure.
(4/11/63
-4-
BC- 250GY
-1
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