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Tuning Procedure
Close the filament start switch which turns on filament and
oscillator.
Set the
filament voltage
to 10
volts with the
filament rheostat.
When
the
30
second time delay relay E6
closes, and if the rear
door
is
closed,
high voltage may be
applied by pressing
the
"High Voltage ON" switch.
With
one
rectifier tube disconnected, slightly under half plate
voltage
will be obtained.
Tune the R.F. driver control C24 for
minimum
current on the
R.F.
driver current meter
M6.
With the reduced
voltage, this should be 40
-
60
milliamperes.
At the same time,
the
power amplifier grid current meter M3 should show
a
reading
of 30
-
60
milliamperes.
The
power amplifier tuning
032 can then
be adjusted for
a
minimum current reading
on the plate current
meter
M4.
This
value should be 100
-
120 milliamperes.
The amount of current
can be controlled somewhat with the "Loading" control
034.
Out-
put current should be indicated on the R.F. Line.Current
meter
Ml,
and should be
approximately half
the
value for
the
particular
transmitter load given in
the
tabulation
of
"TYPICAL VOLTAGE
CONDITIONS" included in this instruction book.
The power amplifier shows no tendencies for parasitic
or self
-
oscillations,
so no
concern need be felt on applying plate vol-
tage without the stage being completely neutralized.
Neutralizing
may be quickly
and
effectively done by tuning
the
plate condenser
C32
through
the
minimum current dip
to
10 or 20
milliamperes
on
each
side, and
watching
the
grid current
as
registered on the
meter
M3.
When first tried, the grid current may show
a
slight
increase on one side or the other
of
the
minimum plate current
dip.
Slowly moving
the
neutralizing condenser
C28,
tune back and
forth across
the
resonance dip with the plate tuning until
a
set-
ting for
the
neutralizing condenser
is
found where
the current
does not increase when the plate
is
tuned off resonance.
The
opposite side will show
a
pronounced decrease
of
grid current.
The
main criteria
is
that the grid current shows no increase from
the
minimum plate current point on either
side
of
resonance, and
decreases
if
sufficient detuning
is
possible.
.
9/11/63
-10-
BC-250GY-1
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