User Manual

3.2 Low Band PA Setup Procedures
1. Set up a 48 V power supply, current limited to a little more than 1.2
amps.
2. Remove both fuses on the power amplifier. Turn both bias potentiometers to
their maximum resistance position ( minimum gate voltage).
3. Apply the 48V supply to the B+ terminal. Verify that the bias (gate)
voltage is at or near minimum by measuring the dc voltage at the gates of
the device. This voltage should be less than 1V. Install one of the fuses
and slowly adjust the corresponding bias potentiometer for 500 mA drain
current. Transfer the fuse to the other side and adjust the corresponding
pot for 500 mA of drain current.
4. Connect a 20 dB, 1 W attenuator to the output of the amplifier as shown in
the diagram below.
5. Install bothl fuses and apply B+ to both supply connections of the
amplifier module.
6. Apply a low level sweep to the amplifier and measure the DC input current
(not more than 1.2 amps) and gain. Gain of the amplifier alone should be
about 20 to 23 dB, and with the preamp in circuit the combined gain should
be between 40 and 43 dB. Flatness over the band should be better than
1 dB, as shown in the following diagram. Curves for chs 2-4 and 5,6 are
correct for the PA alone: