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by powerstat,
T804.
Press high voltage " ON" button on the
amplifier control panel.
Reduce screen voltage to approximate-
ly 400 volts.
It is best at this point to set the screen
grid cirrent switch,
S702, which is located on the amplifier
control panel to the screen current position and monitor screen
current as the transmitter is progressively tuned.
Increase the driver plate voltage in steps to approximately
2,000 volts.
This should give approximately 6 kilowatts out-
put on the amplifier.
Check tuning of the final amplifier with
the control marked " Plate tuning".
It will be noted that wen
tuning the amplifier plate circuit,
the best indication will
be obtained by watching the output meter,
as the amplifier is
quite heavily lorlded and plate current dip is slight.
This is
in accordance with operating characteristics of tetrodes.
They should be operated in a heavily loaded circuit.
It will be noted that the output loading or output coupling
control has a great effect on the power output.
This control
should be adjusted at a point where maximum power and minimum
screen current occur simultaneously.
This will not be the point
where a possible minimum screen current could occur.
This control should be trimmed for m
l
ximum power output every
time the amplifier operating characteristics are changed on
initial tuning.
It is well to note here that the tuning of an FM Transmitter
in the frequency range of 88 to 108 mes offers greater diffi.
culty in regard to tuning various circuits than is normally
encountered on the lower
N frequencies.
This results in great-
er reaction between various circuits caused by small inductance
and capacitive reactances that can be normally ignored at lower
frequencies, but which can become increasingly important at
these high frequencies.
Therefore, when tuning a high fre-
quency transmitter it is well to constantly recheck the pre-
vious adjustment as tuning progresses.
If all of the above conditions exist and all seems normal you
are ready to go to full plate voltage on the amplifier with full
power output.
First, turn the driver plate voltage off and the amplifier
plate voltage off.
Next, place the 6500/3000 volt switch to
the 6500 volt position,
then turn the amplifier plate voltage
on and the driver plate voltage on.
Increase the amplifier
screen voltage to about 800 volts.
Increase driver plate
voltage to the amount required to obtain 20KW output.
àslig
amount of retuning may be necessary on the grid of the ampli-
fier to obtain maximum grid current in conjunction with mini-
mum VSWR between stages.
The plate tuning of the
amplifier
may also have to be adjusted slightly for minimulD plate cur-
6/22/61
-11-
FM- 20B
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