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Model 5065A
Circuit Diagrams, Theory, and Maintenance
POWER SUPPLY AND REGULATOR CIRCUIT
A15 THEORY
The A15 Power Supply and Regulator Assembly pro
vides regulated +20 V.
In addition, there are three other power supply cir
cuits in the A15 Assembly:
a. The full-wave bridge rectifier, energized by
chassis-mounted T 1 , which delivers +24 to 32 volts to
the LC filter consisting of chassis-mounted L1, C1,
and C2.
b. The magnetic field regulator which supplies dc
current for the magnetic field winding in A12 RVFR
Assembly according to the setting of the MAGNETIC
FIELD control on the front panel.
c. The -20 volt supply.
In the +20 volt regulator, +24 to 32 volts connects to
chassis-mounted Q1 and through A14(4) to the +20
volt regulator circuit. Regulated +20 volts connects to
the voltage adjustment R17 which controls Q5A bias.
The other side of differential amplifier Q5A and B is
stabilized by Zener diode CR5 to provide a 9 volt refer
ence.
Q5 output is amplified by FET Q4, used as a
source follower, and A15Q1 to provide bias control of
chassis-mounted transistor Q1. In this way, Q1 output
is held at +20 volts. Overcurrent protection is provided
by the voltage drop of R2 which biases Q3 to drive Q2
and Q1; this turns off Q1. Ripple in the output at A15(8)
is minimized by L2 and C11.
Full-wave bridge rectifier CR1 through CR4 is part of a
basic power supply which includes chassis-mounted in
put transformer T 1 , and LC filter C1, C2, L1 and C7.
The 24 to 32 volt output connects through a blocking
diode on A18 circuit board to the 24 and 32 volt input
of the +20 volt regulator circuit.
The magnetic field regulator consists of differential
amplifier Q6A and B and Q7 which drives the magnetic
field winding in A12 RVFR Assembly.
This circuit
works with the front-panel MAGNETIC FIELD dial to
produce linear control of the resonant frequency of
A12 RVFR Assembly. Since the resonance frequency is
not directly proportional to magnetic field control, fixed
resistances R8 and R12 pad the MAGNETIC FIELD
potentiometer (R6) to provide the required linearity.
Series reference resistors R10 and R11 provide Q6B
with voltage information proportional to magnetic field
winding current. Q6 differential amplifier drives Q7 to
equalize Q6A, B base voltages. In this way, Q7 collector
current through the magnetic field winding is a direct
function of the voltage impressed on Q6A base by the
front-panel MAGNETIC FIELD control.
In the -20 volt supply, +20 volts energizes the saturable
transformer inverter circuit of Q8, Q9, and T 1 .
The
approximate 2 kHz output of T1 is full-wave rectified by
CR6 and 7. C9 provides filtering. -20 volts connects to
the output at A15(11) through voltage regulator Q10,
whose base is referenced at about -20 volts by CR9A
and B, and CR8.
A15 MAINTENANCE
NORMAL OPERATION
The A15 Assembly supplies the following voltages and
currents to power the 5065A.
Pin No.
6
8
11
1,9 Adjustable
Voltage
+20 V ± .2
+20 V
-20 V ± .2
+2 to 4
1
/
2
Current
700 mA
130mA
25 mA
2.5 to 6 mA
In addition, the A15 Assembly has over-current pro- —
tection circuit in the +20 V line.
OPERATIONAL CHECK
a.
Using a dc voltmeter, check voltages at pins 6,
8, and 11. They should be as shown in the above table.
—
b. Connect voltmeter to pin 1 and (see NOTE)
adjust MAGNETIC FIELD dial from 9 to 100. Voltage
_
should be approximately as shown in the table.
NOTE
Be sure to note setting of MAGNETIC
—
FIELD dial before making this adjustment.
The dial should be returned to that setting
after this test.
REPAIR AND ASSEMBLY REPLACEMENT
~
After making repairs, A15R17 should be adjusted. To
do this place the A15 Assembly on the extender board —
provided and adjust R17 so that the voltage at A15(6)
is 20 V + .2 V.
When replacing A15 the output voltage should be ad- —
justed as described above. In addition, AT5R10 and R11
should be removed from the old board and installed on
the new one. This will help maintain the same magnetic
field calibration.
8-64
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