AL-800H Instruction Manual
19
Tuning
Follow the instructions below in numerical order. Proper tuning will produce excellent output power, a
clean signal, and good tube life. If the various meter readings are different than indicated in the text, check
the external amplifier connections. Consult the manual for the exciter if necessary.
WARNING:
The transformer must be wired correctly for your line voltage. This amplifier is
normally shipped wired for standard 240 Vac operation. See the Transformer
Connections section on page 13 for details.
Tuning Procedure
Important Note:
This amplifier contains an electronic grid protection circuit to prevent control-grid
damage. This amplifier will quit operating and the
"OL"
LED will illuminate if the grid dissipation
exceeds a safe pre-set limit.
The overload circuit responds much faster than the grid current meter.
The
overload circuit will respond to excessive grid current before the operator can observe the increase on the
grid current meter.
Some exciters generate high-level RF pulses when first keyed. These short duration pulses may greatly
exceed the exciter's steady-state operating output power. Unexplained activation of the grid overload
circuit may indicate the existence of this exciter problem. The grid overload circuit can be reset by
momentarily placing the
"STBY-OPR"
switch in the
"STBY"
position.
Never under-load the amplifier to reduce the output power. The amplifier
"LOAD"
control must be set to
a high enough position (clockwise) to prevent excessive voltage and arcing in the tank circuit or excessive
grid current. Repeated tripping of the grid overload circuit probably indicates the
"LOAD"
control is set
too low.
1.
Set the AL-800H front panel switches as follows:
POWER
to
OFF
OPR-STBY
to
STBY
MULTIMETER
to
HV
2.
Plug the ac line cord into the proper voltage outlet.
3.
Place the main power switch in the
"ON"
position. The meter lamps should light and the blower
should start. Read the 3500 volt scale on the multimeter. It should indicate 2600 volts nominal and no
more than 2700 volts.
4.
With the amplifier still on
"STBY"
, tune the exciter into a normal 50 ohm load according to the
manufacturer's instructions. Turn the exciter drive down after tuning.
