Instruction manual

AL-800 Instruction Manual
18
"PLATE" Control
The
"PLATE"
control adjusts the output tank circuit to resonance. This control should always be
adjusted for maximum RF output power. Maximum RF output power normally occurs
simultaneously with maximum grid current and very close to the plate-current "dip."
"LOAD" Control
This control adjusts the coupling of the amplifier to the antenna. This adjustment is necessary to
insure optimum coupling to the load as the SWR of the load, the operating frequency, or the power
level is changed. Advancing the
"LOAD"
control clockwise increases the RF power output
capability and the linearity of the amplifier. Advancing the
"LOAD"
control also decreases the
grid current and increases the plate current for a given amount of drive.
The efficiency of the amplifier and the grid current decrease if the
"LOAD"
control is rotated
beyond the point of maximum output. The linearity, however, will increase. The proper position
for this control is slightly clockwise from the setting that produces maximum output with full drive-
power applied. Never use this control to adjust the output power.
CAUTION:
Failure to adjust the loading control properly can result in excessive tank
circuit voltages and damage to components.
The
"PLATE"
control should always be checked after the
"LOAD"
control is adjusted by more
than one number. For example, if the
"LOAD"
is advanced from 1-1/2 to 2-3/4, the
"PLATE"
should be re-tuned. If the
"LOAD"
is touched up a small amount, the
"PLATE"
setting will not
usually require re-adjustment.
Driving Power
This amplifier is designed to operate at full ratings when it is driven by an exciter that has
approximately 85 watts of RF output. An exciter with a lower output power may be used with a
resulting decrease in amplifier output. Both the driving power and the
"LOAD"
control must be
carefully adjusted when using an exciter that delivers more than 85 watts. Proper control settings
will help prevent excessive grid current and spurious signals, which create needless interference to
other operators. A monitor scope is recommended for continuous output observation. An
oscilloscope is the best way of determining if the amplifier is "flat-topping" and producing excessive
distortion products.
A second method of determining linear operation is to monitor the peak RF output power carefully
on the AL-800's internal meter. Determine the maximum obtainable RF output power and reduce
the exciters power until there is a noticeable margin from the maximum output power. This will
insure some reserve power is available for random voice peaks.
Note: Never increase the drive power beyond the point where the amplifier's output power
stops increasing. This is also the point where the grid current will begin rising rapidly.