Specifications

R.5.14.1 Driver Tuning
The Driver Combiner pipe is tuned to series resonance by the
Driver Tuning Assembly. A binary combination of inductor L1
through L6 and capacitors C1 though C6 are switched by vacuum
relays K1 through K5. The Driver tuning is a 5 bit signal that
breaks the frequency range into 31 bands.
R.5.14.2 Driver Level
The Bit 0 output is a 2 band output for switching the toroid T1
via K1 into the boost (de-energized)/no boost (energized) con-
nections.
R.5.15
Servo Circuit Descriptions
The main purpose of the servo drive circuits is to allow the PA
tuning and loading to be quickly adjusted to the optimum point
for each given frequency.
The servo circuit requires a reference voltage which determines
the correct servo position. The reference voltages required for the
servos are recorded on the Transmitter Band Chart for the differ-
ent frequencies. The position voltage is feedback from a poten-
tiometer mechanically connected to the servo mechanism. When
the servo is activated, the servo will always try to make the
position voltage from the feedback pot the same as the reference
voltage.
NOTE
The SERVO REFERENCE PAL U22 is not used in this applica-
tion.
R.5.16 Tune Servo Assembly
The Tune Servo motor B1 in the 2A6 Servo Drive Assembly is
connected via a gear assembly to 3 variable capacitors, 2C1B
through 2C1D. This group of three capacitors is connected across
fixed capacitor 2C1A. As the servo is varied,the total capacitance
changes, and the input bandpass filter is tuned to resonance.
R.5.17
Tune Servo Amplifier
The Tune Servo Amplifier U41 is a high power operational
amplifier in a TO-3 case mounted on the heatsink underneath the
board.
The +17/-15VDC supplies are connected to the supply pins.
This amplifier will compare the reference voltage at the (-) input
with the servo position voltage at the (+) input. If there is a
difference in the two voltages, the servo amp output at J14 will
produce sufficient current of the proper polarity to drive the servo
motor B1 to the correct location and make the position voltage
the same as the reference.
The Tune Gain feedback potentiometer R81 is adjusted so that
when the circuit is active, hunting or oscillations do not occur in
the system.
Feedback resistors from the output limit the maximum drive
current to 6.5A, and diodes from the output to the supplies
clamps any voltage spikes for driving the inductive load.
R.5.18
Digital Reference Circuit
The function of the Digital Reference circuit is to develop the
reference voltage for the servo amplifier. This voltage is varied
in increments as a function of the particular frequency chosen.
A frequency shiftable digital up/down counter and digital poten-
tiometer is used to provide coarse/fine adjustment of the refer-
ence voltage as needed during the different tuning modes.
R.5.19
Tune Reference Digital Potentiometer
The digital reference circuit consists of an 8 bit digital potenti-
ometer U33, which will produce an output voltage of negative
0-14VDC depending on the 8 bit input.
The Tune Upper Limit pot R510 sets the maximum +14VDC
input reference voltage possible, which corresponds to the upper
mechanical stop of the assembly.
If all 8 DB0 through DB7 inputs are logic high, the output voltage
at U33-1 will be +12.7VDC. When all inputs are logic low
(except DB0 discussed later), the output will be 0VDC. The
output reference voltage is inverted and connected to the Tune
Reference Bypass Jumper JP3.
When JP3 is in the Normal position, the output is connected to
inverter buffer. If in the Bypass position, the servo can be manu-
ally tuned with the Tune Bypass Reference Adjustment R91.
R.5.19.1 Inverter Buffer
The negative 0-14VDC input is inverted to a positive voltage by
U31 and connected to the Servo Amplifier (-) input, the Tune
Servo Fault Detector, and the Tune Reference Multimeter at J19.
The Tune Lower Limit pot R511 is adjusted so that when the
input is 0VDC, the output is approximately +.7VDC. This cor-
responds to the lower mechanical stop of the assembly. (This
voltage is 1.2VDC for the Load Servo).
R.5.20
REFERENCE COUNTER PAL
The REFERENCE COUNTER PAL is a 5 bit two frequency
up/down counter that controls the digital pot that provides vari-
ations in the reference voltage. It also contains some of the logic
for detecting a Tune Servo Fault.
Refer to Figure R-3 REFERENCE COUNTER PAL Encoder for
the following example.
R.5.20.1 Up/Down Counter Clocks
When in the Frequency Change mode, the clock input from the
SERVO PAL will be 12.5Hz and the active high Raise/Lower
inputs will cause fast up/down binary counting of the 8 bit output
and corresponding servo movement.
When in the Low or High Power Tune modes, the clock input
from the SERVO PAL will be 3.1Hz and the active high
Raise/Lower inputs will cause slower up/down binary counting
of the 8 bit output and corresponding servo movement.
R.5.20.2 Counter Reset
The highest up count 8 bit output is all logic high. The lowest
down count output is 00000001 from DB7 to DB0 respectively.
If the A/C power is lost and the battery backed-up +5VC is
depleted, the Reset input will be logic low. When the power
R-6 888-2339-002
WARNING: Disconnect primary power prior to servicing.