AMERITRON AL-80B, Instruction Manual

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AL-80B Instruction Manual
17
ALC Limit Adjustment (rear panel)
This adjustment procedure should be used if "pumping" occurs from excessive transceiver ALC
sensitivity and/or slow transceiver ALC response time:
1. Load the amplifier for maximum output on any band (see tuning instructions later in this
manual).
2. Adjust the "ALC SET" control on the front panel and the rear panel "ALC Limit" potentiometer
to their full counter-clockwise positions.
3. Apply full exciter drive power, and adjust the rear panel "ALC Limit" potentiometer clockwise
(rear view) until the amplifier's ALC output voltage meter (multimeter "ALC" position)
indicates 6 to 10 volts. As an alternative, the potentiometer can be adjusted clockwise until the
RF output power reaches 300-500 watts.
4. Adjust the front panel ALC SET control to the desired power level.
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-80B'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.
The amplifier is 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.