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minutes after first turning the unit on.
Stray capacities of
tubes tend to change slightly as the tube warms up and a small
change of even 1/4 pf can considerably de- tune a circuit operat-
ing in the VHF range.
Frequency adjust control 0104 should be set to the value given
in the factory test data sheet.
Oven pilot lamp A101 will
start cycling after the oven heater has been on for about 20
minutes.
The crystal oven does not really stabilize until it
has been on for about 1 hour.
If,
after this length of time,
the carrier center frequency does not agree with that shown on
a frequency monitor of know accuracy,
readjust the C104 for
proper center frequency.
Normal cycling of oven pilot lamp
A101 will be"ON" 1/3 and " OFF" 2/3 timeswise for a room temp-
erature of 75
0
F.
A quick check of the 13
7
Z voltage is advisable.
This can be done
by placing the negative probe of a 20,000 ohms per volt meter
into a black test point ( TP122 or TP123),
and a positive probe
into TP121.
The voltmeter should read .320 volts DC.
DAILY OPERATION
It is considered good practice to arrange wiring and control
circuits so that the crystal oven heater operates independ-
ently of the main power switch.
If this is done,
and the
crystal oven remains on all the time, the exciter will be close
to center frequency,
even fro': a cold start. Power requirements
for the oven are about
6
watt and this only intermittently;
On a presumed basis of the oven being " ON" 1/3 of the time,
the oven would use only 2 watt of power per hour.
Assuming that the crystal oven is ón continuously, then the
only thing that needs to be done in the normal
days
operation
is to turn the main power " ON" when starting the oreadcasting
day and " OFF" when finished.
In most cases, this will be
accomplished when the low voltage switch is turned on in the
transmitter, whether the transmitter be 250,
1000 or 5000 watts.
If the exciter is turned on 10 or 15 minutes before . TAIR" time,
no other adjustments should be necessary.
The exciter will
reach
S O
to 90% of full power in about
5
minutes and full power
in 10 to 15 minutes.
This assumes that the unit was fine tuned
while thoroughly warmed up.
-5.
M6095 Exciter
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