Palstar COMMANDER HF-2500 EXPORT, Owner'S Manual, Page: 14 / 30

14
Theory Of Operation
The Commander HF-2500/HF-2500 M
AGNUM
uses a pair of C.P.I. Eimac 3CPX800A7
pulse rated ceramic/metal triodes in a class AB
2
grounded grid configuration. Nominal drive
power of 20 to 60 Watts will produce 1500 Watts of clean RF output power.
This amplifier will operate on the following amateur bands: 160, 80, 40, 20, 15, 17, 12 and
10 meters.
Metering Functions
The Commander HF-2500/HF-2500 M
AGNUM
has two illuminated cross-needle panel me-
ters. The left-hand meter continuously displays 3CPX800A7 grid current and relative output
power. Under typical operating conditions the grid current will be 20-50mA.
Plate voltage and Plate current are continuously displayed on the right-hand meter. The
typical plate current under nominal rated output (1500 Watts) should range from approximately
700mA to 800mA on the HF-2500, and 900mA to 1100mA on the HF-2500 M
AGNUM
, with an
absolute maximum of 1200mA.
Tuned Input Circuits and Adjustments
The tuned input circuits utilize an
π
impedance matching circuit with a high
Q
design.
These circuits employ RF phase compensating capacitors to reduce intermodulation products.
The use of mica trimmer capacitors allows adjustments to match the transceiver to the ampli-
fier. The rear panel provides easy access to these trimmer capacitors. A front panel band switch
selects the appropriate input filter.
Your Commander amplifier has mica trimmer capacitors which are easily accessed thru
holes located on the rear panel. The tuned input circuits are factory tuned and should not be re-
adjusted unless necessary. You can easily make adjustments for any change in your preference
for operating frequency range. Also, slight adjustments may be necessary because of slight vari-
ances in impedances between your transceiver and the tuned input circuitry of the amplifier.
1. Install a SWR meter between the transceiver and the amplifier.
2. Make sure the Standby/Operate switch is in the Operate position and the band switch
is set to the same band as the one for which you are making adjustments. Your ampli-
fier should also be properly tuned and loaded (preferably onto a dummy load of suffi-
cient capacity).
3. Apply drive, observe the SWR, and adjust the trimmer capacitor for minimum SWR.
Be careful not to overdrive the amplifier.
4. Repeat this procedure for each band.
Automatic Level Control and Adjustments
An adjustable Automatic Level Control (ALC) circuit limits the peak output power. When
properly set, this circuit insures that the amplifier can not be overdriven. Rear panel access al-
lows for easy manual adjustment. A sample of the RF input derives the ALC voltage.
Your transceiver's internal ALC will maintain linearity. The amplifier's ALC will prevent
overdriving the amplifier. The HF-2500/HF-2500 M
AGNUM
's ALC circuit was designed for
negative going ALC voltage. Proper adjustment is as follows:
1. Use an insulated tool when making these adjustments.
2. Tune the amplifier for operation on the 20 meter band for full 1500 watts output.