Calibrator Section; Power Supply Section; Detailed Description; Rf Generator Section - HP 608E Operating And Service Manual

Model 60aE/F
4-17. CALIBRATOR SECTION.
4-18. The Calibrator Section consists of5-MHz Oscil-
lator V9A, I-MHz Oscillator V9B, Amplifiers VIOA
and VH, and the associated circuits. Operation of
the oscillators is controlled by the XTAL CAL toggle
switch that has three positions; OFF, 1 MC, and 5
MC. With the selector switch in either the 1 Me or
5 MC position, an output from the active oscillator is
mixed wtth a sample RFsignal from Power Amplifier
V6 in the RF Generator Section to produce audio beat
signals. The audio signals are passed through ampli-
fiers VIOA and Vll to a matching transformer. The
transformer output is then applied to XTAL CAL
OUTPUT connector J3 for use by an operator during
frequency calibration operations. A XTAL CAL GAIN
control cOMected in the output circuit of Amplifier
Vll provides an audio output level adjustment.
4-19. MODULATION METER SECTION.
4-20. The Modulation Meter Section consists of sta-
bilized wideband amplifiers V18 and V19, rectifier
V20,
and
twin-triode V21 cOMected
in
a bridge cir-
cuit. Prior to operation the PERCENT MODULA-
TION meter, also connected in the bridge circuit, is
calibrated by use of the Meter Calibration control, an
internal adjustment. Also, the bridge circuit is bal-
anced to electrical zero by the ZERO adjustment
located on the front panel of the instrument. The R F
Signal output of the Attenuator Section is detected
across diode CR2 and applied to a filter network that
produces the modulating signal. 'Phis signal is ampli-
fied in via and V19, rectified in V20, and applied to
the bridge circuit. The bridge circuit is unbalanced
in direct proportion to the-peak amplitude of the input
modulaUng signal; therefore, the PERCENT MODU-
LATION meter connected across the bridge indicates
the degree of unbalance in the bridge, or the percent-
age of modulation, The percentage of modulation is
established by use of the MODULATION control in the
Amplitude ModulaUon Section.
4-21. POWER SUPPLY SECTION.
4-22. The Power Supply Section consists of four
series-regulated interrelated power supplies. The
+225-volt power supply contains Comparison Ampli-
fier V12 and a Series Regulator comprised of both
sections of VI3 and V16a. The +25-volt power sup-
ply contains Reference Amplifier QlO and Series Reg-
ulator QI1. The -165 -volt power supply consists of
Reference Tube VIS, Comparison Amplifier V14, and
Series Regulator v16A. The -6.3 volt supply con-
tains a reference diode and Series Regulator Ql. The
-165 volt supply is used to reference both the -6.3
volt and +225 volt supplies. The +225 volt supply is
used to reference the +25 volt supply. A further dis-
cussion of these power supplies is contained in the
detailed circuit description that follows.
4-23. DETAILED DESCRIPTION.
4-24. This discussion describes the circuits in the
RF Generator Section (Model 60SE), RF Generator
Section IV
Section (Model 60SF), Amplitude Modulation Section,
Attenuator Section, Calibrator Section, Modulation
Meter Section, and the Power Supply Section. Figures
7-4 and 7-5 will be used as reference during the des-
cription, and where tr:;,nsition from one diagram to
the second is required appropriate notice will
be
made.
4-25. RF GENERATOR SECTION, MODEL 608E.
4-26. The RF Generator Section in the Model 60SE
includes RF Oscillator V6, Buffer Amplifier V22, and
Power Amplifier VS. RF Oscillator V6 is a type 4042
triode connected across the +225 and -165 Vdc sup-
plies in a Colpitts circuit. The oscillator tank cir-
cuit contains split-stator capacitor CI7A and five
separate RF transformers mounted on a revolving
turret assembly. Capacitor segment CI7A is mech-
anically linked to segment C17B in the output circuit
of Power Amplifier V8, and the oscillator turret as-
sembly is linked to an amplifier turret assembly also
located in lhe output circuit of VS. Choice of frequency
band
1s made by operating the FREQUENCY RANGE
switch located on the front panel of the instrument.
This function rotates the oscillator and power am-
plifier turret assemblies simultaneously to the se-
lected range (Range A through E), and sets the asso-
ciated inductor (LI through L6, and Ll2 through L16)
into the output circuits of RF Oscillator V6 and Power
Amplifier VS respectively. Capacitors Cl7A and
CI7B are then tuned by the front-panel mounted Fre-
quency Control to the desired frequency within the
range. Minor frequency adjustments can be made by
tuning capacitor C68 (FINE FREQ control) in the tank
circuit of Oscillator V6.
4-27. The plate circuit of RF Oscillator V6 is series
fed through resistors R246 and R247. These resis-
tors in conjunction with resistor R43 in the cathode of
the stage serve to limit plate current within safe
limits. The cathode of Oscillator
V6
is bypassed by
capacitor C25, which is part of the tube mounting plate
and Is not visible when the plate is in positIon. Bias
for the stage Is developed by cathode resistor R249
and grid resistor R248, with coupling capacitor Cl6
returning feedback to the grid to maintain oscillation.
Capacitor C59 connected across a portion of the tuned
circuit is used to calibrate the high end of the frequency
dial after replacing an oscillator tube. Capacitor
C18, installed in the Model 60BE only, is used to im-
prove tracking characteristics of the tuned circuit at
higher frequencies. Adjustment of this internal con-
trol is critical, since a compromise must
be
reached
between tracking capabilities and optimum power out-
put. Misadjustmentof capacitor CIS can produce im-
proved tracking capability but a loss in RFpowerout-
put. The control is factory aligned, and no further
adjustment should be reqUired.
4-2S. All voltages applied to RF Oscillator V610cated
in the RF Generator hOUSing assembly are regulated,
and brought into the stage through RFl filters. The
+225 vdc plate voltage is received through filter FL5,
the -165 Vdc supply is received through filter FL2,
and
a regulated -6.3 heater voltage is received through
filter FL4.
4-3