Technical description
HF SSB Transceiver 9323/9360/9390/9780 Technical Service Manual 4-31
Driver stage
The push–pull, class B, driver stage V21 and V22 is voltage driven from the
secondary of T2. The transformer T3 provides the current drive to the output
stage.
The bias for the driver stage is applied to the centre tap of T2. This is provided by
the total current of the emitter follower and pre-driver stages (V15 and V16) via
transistor V17, which is connected as a diode. The bias is set by the SOT resistor
R54 and changes the voltage drop across the collector-emitter of V17.
Output stage and bias regulator
The push–pull, class B, output stage V23 and V24 is driven from the centre tapped
secondary winding of transformer T3. The centre tap provides the bias feed from
the bias regulator.
The bias regulator V19 and V20 provides a constant voltage to the bases of V23
and V24. The transistors V19 and V20 form a feedback voltage regulator. The
output voltage is the base-emitter voltage of V19 and is adjustable by the preset
potentiometer R59. The transistor V19 is mounted on the PA heatsink and
provides temperature compensation to the bias network.
When low power is selected, the microprocessor (via the serial bus) latches IC1
pin 11 low. This energises the transistor V25 and changes the current through
V19. The result is an increase in standing current to the output transistors V23 and
V24. This increase in bias improves the intermodulation distortion at low power.
The zener diode V18 and resistor R61 increase the bias for a low DC supply
voltage (< 11 V). This, in conjunction with the power output reduction circuit in
the ALC (see page 4-32, ALC control), reduces the intermodulation distortion
when operating from a low DC supply.
The balanced/unbalanced impedance matching output transformer T4 couples the
power amplifier output to the band filters via the transmit/receive relay K7.
Output filters
The transmit frequency range is dependent on the PA assembly fitted and uses six
LPFs, which are selected by relays K1 to K6. These are operated from IC1 and are
selected to remove the harmonics generated by the PA.
The output of the filter circuit passes through the ALC RF bridge to the antenna
output J1.
PA assembly 2.25 to 30 MHz has an optional external filter to increase the lower
range to 1.6 MHz. The filter is attached to the rear of the heatsink and is relay
selected by a low on IC114 pin 18 [104-02976] via the antenna control
connector J202/2.
To Next Page
Loading...
Need help?
General
