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Model 5065A
Circuit Diagrams, Theory, and Maintenance
'aractor A2A1CR1 capacitance decreases as the biasing
oltage applied from A9 Assembly through J1 (-EFC)
-increases positively producing an oscillator frequency
icrease.
In this manner, oscillator frequency is cor
s e t e d by the dc error voltage to maintain frequency
stability with respect to the Rb
87
resonance. The other
;
nput to Varactor A2A1CR1 is the FINE Oscillator Fre-
uency input through J2 (+EFC) from the front-panel
-^INE knob.
This control is normally used only for
testing and with the instrument operating, is set at 250.
he A2A2 AGC Assembly contains two tuned 5 MHz
-amplifiers, the AGC circuit, and the 6 and 15 volt power
supplies. The +6 volt supply is used as A2A1Q1 col-
sctor supply and as A2A2Q1 and A2A2Q2 bias supply.
he +15 volt supply is the reference voltage for R3, the
Tront panel Oscillator Frequency FINE adjustment.
he open-loop gain of tuned amplifier A2A2Q1 is ad-
_jsted by A2A2R3; the closed-loop gain of A2A2Q1 an
A2A2Q2 is determined by feedback resistor A2A2R9.
A2A2C5 tunes A2A2Q1 collector resonance.
Second
ined amplifier stage A2A2Q2 provides output power
- J 5 MHz to A10A3. One secondary winding from out
put transformer A2A2T2 provides a feedback signal that
'- in phase with the input signal at A2A2Q1 base; this
gnal is fed back to A2A2Q1 emitter through A2A2R9
-ror gain stabilization of the amplifier pairs; to A2A2Q2
base through A2A2C3 for neutralization; and through
2A2C13 to AGC detecting diodes A2A2CR3 and
. _2A2CR4.
A2A2C11 tunes A2A2T2 for resonance.
Diodes A2A2CR3 and A2A2CR4 provide a dc voltage
-oportional to the 5 MHz output voltage level this volt-
je is algebraically added to the bias voltage estab
lished
by
A2A2R11
and
AGC
gain
adjustment
A
2A2R12. The resultant voltage is fed back to the base
:
A2A1Q1 oscillator stage for bias control to regulate
^oCillator drive level to the quartz crystal.
,
0A3 POWER AMPLIFIER
The A10A3 assembly contains the 5 MHz output ampli
fiers and the dc controller circuit which supplies dc
i rrent for the oscillator oven heater. For a discussion
c_ the dc controller, see "Proportional Temperature
Control Circuit" at the beginning of this section.
i
MHz from A2A2 couples through A3C1 to buffer
emiplifier A3Q1. Selected resistor A3R9 sets A3Q1 gain
for the correct ouput at J4 (factory adjustment).
This
; ige feeds adjustable crystal filter network of A3Y1
,
E12, A3C9, 5 MHz crystal filter adjustment A3C10,
A3C11, A3C6, and A3C8.
Capacitor A3C6 and A3C8
provide ac voltage division for the 5 MHz output to the
i
Frequency Divider Assembly.
Emitter follower A3Q5 couples the filter network to out
put amplifier A3Q6. The gain of A3Q6 stage is adjusted
I
A3R19 and collector resonance is tuned with A3C12.
Cjtput transformer A3T1 feeds the A3 Multiplier As
sembly through A3J3.
Supply voltage filtering is supplied by A3L1 and A3C5
for A3Q1 and by A3R11 and A3C15 for A3Q5 and A3Q6.
Additional RF decoupling for A3Q1 is supplied by A3R5
and A3C3.
A10 MAINTENANCE
The oscillator assembly is not recommended for field
repair. Instrument warranty is void if repair or adjust
ment is attempted inside the assembly.
Adjustments
other than those available on instrument front panel will
also void the warranty.
If it is established that a de
fective component or circuit trouble exists within the
oscillator
assembly,
contact
the
nearest
Hewlett-
Packard Sales and Service Office for shipping instruc
tions (see paragraph 2-10 for packing information).
OPERATIONAL CHECK
The following procedures may be used to determine
proper operation and should be used if the assembly is
replaced.
CIRCUIT CHECKS.
The following circuit checks in
volve checking oscillator inputs and outputs.
a. Set instrument to normal operation with front
panel MODE switch set to LOOP OPEN.
b.
Disconnect the +20 red wire from the oscillator
assembly.
Connect a high impedance dc voltmeter
positive lead (+) to the disconnected red wire. Connect
comman (-) voltmeter lead to instrument chassis. Volt
meter should indicate +20 V.
Disconnect voltmeter
and connect red wire back to +20 terminal on oscil
lator assembly.
c.
Disconnect the +24 white-red-blue wire from
oscillator assembly.
Connect a high impedance dc
voltmeter positive lead (+) to the disconnected white-
red-blue wire. Connect common (-) voltmeter lead to
instrument chassis. Voltmeter should indicate between
+22 and +33 volts.
Disconnect voltmeter and connect
white-red-blue wire back to +24 terminal on oscillator
assembly.
d.
Connect high impedance dc voltmeter to wht-
orn wire on OSC FREQUENCY XIO"
10
control. Connect
common (-) lead to chassis ground. Voltmeter should
indicate between +14 and +16 volts.
Disconnect
voltmeter.
e. Connect dc voltmeter to OSC OVEN pin on
Terminal Board Assembly A17(5). Connect common (-)
lead to chassis ground. Voltmeter should indicate about
+16 volts. Disconnect voltmeter.
f.
Connect
an
oscilloscope
vertical
channel
through a 50-ohm feedthru to A10P3.
Oscilloscope
display should be 5 MHz, 3 V peak-to-peak.
Remove
oscilloscope and replace A10P3.
8-51
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