Instruction manual

AL-800 Instruction Manual
22
adjusted until the ALC voltage meter slightly flickers (ALC position of the
"MULTIMETER"
switch) while operating with normal output power levels.
The ALC circuit will limit the amplifier's grid current to a safe value if anything accidentally
changes in the station or the antenna. The CW keying waveform of the radio will remain unaltered
when the ALC is adjusted in this manner.
Note: Caution should be exercised if the "ALC SET" is used to control the CW power output
with the exciter power control set at maximum. Key clicks may be produced if the
exciter has a poor ALC response time. Check for proper wave shape when using the ALC
in the amplifier exclusively to control the RF output power.
Rear-Panel "ALC LIMIT" Control
The
"ALC Limit"
control (rear panel) limits the maximum voltage available from the ALC circuit.
This control is necessary only because the ALC response times and voltage requirements for
exciters have never been standardized. The ALC voltage requirements may even vary between
different models produced by the same manufacturer.
If the ALC response time of the exciter (transceiver) is faster than the rise time of the RF envelope,
there will be no voltage compatibility problems. The ALC voltage from this amplifier will
automatically adjust to the limit required by the exciter.
If the ALC voltage requirements are low and if the ALC attack time is slow, the ALC may cause the
output power to "pump" at a very slow rate. The undesired "pumping" can be corrected by reducing
the amplifier's ALC output voltage with the
"ALC Limit"
control (R1).
A full counter-clockwise
"ALC Limit"
setting will produce approximately 10 volts of maximum
negative ALC voltage. A full clockwise setting (viewed from amplifier rear) will produce no ALC
voltage. Always start with this control fully counter-clockwise before slowly advancing this control
clockwise. The
ALC Limit Adjustment
section that follows gives adjustment details.
An external 1,000 to 5,000 ohm potentiometer can be added from the ALC output line to ground if
the particular amplifier you are using does not have a rear panel
"ALC Limit"
control. The chassis
(shield) of the amplifier's ALC output jack must connect to the clockwise (shaft end view) terminal
of the ALC exciter voltage control. The ALC jack center pin on the amplifier must connect to the
counter-clockwise terminal (shaft end view) of the external control. The center of the control
connects to the ALC input of the exciter.
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).