Palstar COMMANDER HF-2500 EXPORT, Owner'S Manual, Page: 15 / 30

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3. With your transceiver set for 20 meter SSB operation, set the transceiver's microphone
gain for normal operation as specified in its owners manual.
4. While speaking louder than normal into the microphone, adjust the ALC pot through the
access hole on the rear panel . Adjust for 1500 Watts maximum output as indicated on
an external peak reading Wattmeter.
5. On some newer model transceivers this adjustment can be made in the CW position. On
these models (with your output at 1500 Watts) simply adjust for a slight drop in output.
Output Filter Circuit
The π variable network filter transforms the plate load impedance from approximately 2500
Ohms down to 200 Ohms, Two air variable capacitors and an associated inductor accomplish
this transformation. A heavy duty band switch selects the proper inductance from high
Q induc-
tors with appropriate taps for the desired band of operation.
A design
Q
of 14 allows for good harmonic attenuation on all bands. A special reactance-
tuned ferrite core 4 to 1 transmission line transformer steps down the 200 Ohm output of the π
circuit to the 50 Ohm nominal antenna impedance. This also provides further harmonic attenua-
tion of the output in the same manner as an L coil in a π-L network.
High Voltage Supply
The high voltage supply operates from 200/234 VAC, 20 Ampere line. The primary of the
high voltage transformer is switched on and off with relays and incorporates a step-start circuit
to limit in-rush current while the high voltage filter capacitors charge. The front panel On/Off
switch applies AC mains power to the controller circuitry which then controls AC power to the
filament and HV transformers. In the HF-2500 approximately 900 VAC is applied to a full
wave voltage doubler circuit. In the HF-2500 M
AGNUM
, 2400 VAC is applied to a full wave
bridge. Metering of the tube anode and grid current is accomplished by shunt resistors located
in the negative return of the 3CPX800-A7 cathode. Plate voltage metering is accomplished by a
resistor divider network in the B+ line of the high voltage circuit.