Instruction manual

AL-800 Instruction Manual
19
The amplifier being over-driven for a given
"LOAD"
setting when the grid current increases
rapidly while the plate current and output power increase slowly. The amplifier
"LOAD"
control
needs to be advanced to a higher number if this condition occurs. Non-linear operation, splatter,
and
excessive grid current will occur if the
"LOAD"
setting is too low. Excessive plate current is the
proper indicator that the drive power limit has been reached.
Tube and Component Life
These guidelines will help prolong tube and component life, and minimize splatter.
1.) On SSB or other linear modes virtually any amount of power will cause splatter if the loading
is too light (
"LOAD"
control too far counter-clockwise). Always tune for maximum output
with maximum drive power. Reduce the drive power to reduce the output power on SSB, not
the loading control.
2.) Lightly loading an amplifier will also result in large voltages building up in the tank circuit.
Under-loading an amplifier is much harder on the tube and other components than operating a
properly loaded amplifier into a high SWR or with excessive drive power.
3.) Never depend on average reading power or current meters to indicate proper operation on SSB
or other linear modes. The best indicator of linearity is either an oscilloscope or the internal
PEP RF output meter. Maximum linearity can be determined by finding the maximum output
power possible and then reducing the exciter power for a slight reduction in output power.
4.) Never exceed 25 mA of grid current on CW carrier. The proper grid current during voice
modulated SSB will range from 0 to 12 mA, and will typically be at 5 mA or less. The SSB
grid current will vary with the operators voice, the amount of signal compression or processing,
and the tube characteristics.
Additional SSB Notes
The peak power output developed on SSB is limited by the amplifier loading, RF drive, and peak-
to-average power of the RF wave form. The
"LOAD"
setting is the single most critical adjustment
for proper operation. Properly loaded, this amplifier will produce excellent linearity with output
powers of well over one kilowatt. Improperly adjusting the
"LOAD"
control can produce flat-
topping and splatter with only a few hundred watts of RF output.
Note:
Always remember that the
"LOAD"
control setting is much more important than any other
parameter for good linearity!
To maintain linearity, always be sure that the
"LOAD"
control is adjusted far enough clockwise for
the peak drive that will be applied.
Be considerate of others. NEVER "push" this amplifier into envelope clipping or to the point where
the grid current approaches 12 mA on voice peaks. Envelope clipping can be also be avoided by
adjusting the amplifier's
"ALC SET"
control until the peak output power drops slightly from the