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User's Manual | ACOM 1500 | HF + 6 m Linear Amplifier
August 2021 S e c t i o n OPERATION | Page 29 of 52
If, for some reason, matching cannot be accomplished successfully, check BAND switch position and proper
antenna selection. Then check the antenna SWR at the same drive frequency.
d) Tuning hints
While turning the knobs, you will note that both tunings would be virtually independent. This is a benefit of
the TRI. The plate-load resistance increases to the right and decreases to the left of the TRI center.
The center of the scale corresponds to the proper
LOAD capacitor tuning, which presents an optimum load
resistance to the tube.
If you tune to the right, you will obtain more gain, but less undistorted output power will be attainable. You
may prefer to use this hint when your drive power is insufficient or when you need less output but better
efficiency, for instance at heavy duty modes (RTTY, SSTV, etc.) where less heat is wanted (not only in the
amplifier but also in the transceiver).
Tuning to the left of the center would lead to the opposite: less gain and more power attainable. Of course,
this requires more drive power, more plate current, and more plate heat, which shortens tube's-expected
life, as its cathode would be faster exhausted.
О ff-center tuning may also be used to compensate for line (mains) voltage variations in order to maintain
tube efficiency. In that case, tune to the right when mains is higher, or tune to the left if it's lower than the
nominal voltage. However, where there is more than a 5% difference from the nominal line (mains) voltage,
the voltage selector inside the amplifier should be changed (see Section
2.2 Line Voltage Selection
).
4.5. Continuous Carrier Modes
The maximum output power in continuous carrier modes such as RTTY etc. is 1200 W. You may exceed this
limit up to about 1300 W for short periods (one minute or less), while adjusting the drive power for instance.
Please, have in mind, that the mean output power should not exceed 1200 W for longer periods.
For prolonged transmissions the amplifier gain can drop between 5% and 10% during the first minute which
is normal while temperature balance of the tube is achieved. You can easily compensate this by increasing
the drive power slightly. Once the drive power has been set, the output power remains stable with the time
for hours.
NOTICE
For transmissions longer than 15 minutes the external auxiliary fan must be installed
(see Section
2.5 Installation of External Fan
).