AL-800H Instruction Manual
18
Driving Power
This amplifier is designed to operate at full ratings when it is driven by an exciter that has approximately 70
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 70 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-800H'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. If this
happens, the LOAD control is set too far counter-clockwise and needs to be adjusted to a
higher number.
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, while excessive grid current indicates improper loading.
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
60 mA of grid current on CW carrier. The proper grid current during voice modulated
SSB will range from 0 to 20 mA. The SSB grid current will vary with the operators voice, the amount
of signal compression or processing, and the tube characteristics.
