Power Supply Section - HP 608E Operating And Service Manual

Section IV
V20, and a balanced-bridge circuit containing PER-
CENT MODULATION meter M2. The Bolometer is
illustrated in Figure 7-4, and the remainder of the
section appears in Figure 7-5.
4-61. The output of diode CR2, capacitor C38 and
resistor R119 in the Bolometer is a dc Signal which
is representative ofthe RF output level, and the modu-
lating signal when internal or external modulation is
in process. The output is passed through RFI filter
FL8 and applied to blocking capacitor C39, which
couples the modulating signal to Amplifier VI8. The
output of Amplifier VI8 is amplified again in VI9 and
passed to the plates of Rectifier V20. A stabilization
feedback circuit connects the plate of Amplifier VI9
and cathode of Amplifier VI8, with resistor R99
installed in the circuit for frequency compensation.
CS5 ac couples the plate ofV19 to the cathode ofVl8.
4-62. Rectifier V20 is connected in a balanced-bridge
detector circuit consisting of twin-triode V21, PER-
CENT MODULATION meter M2, and associated cir-
cuitry. With no modulating signal applied tothe circuit,
the steady-state dc potential at the plate of Amplifier
V19 is coupled to the grids of V21A and V21B. Inthis
condition, equal current flows on both sides of tne
bridge, and the PERCENT MODULATION meter reads
zero. ZERO potentiometer RI06 is a front-panel ad-
justment to compensate for variations in tube and com-
ponent values. When a modulation mcxle of operation is
in progress, the peak value of the rectified modulating
signal is applied to the grid of V21B. The bridge is
unbalanced accordingly, and produces an indication
on the PERCENT MODULATION meter that is indirect
IJJ'vportion to the amplitude of the modulating Signal.
Triode V21A is unaffected during the detection cycle,
since the modulating signal is filtered by resistors
RIOO, RI01, and capacitor C5a.
4-63. POWER SUPPLY SECTION.
4-64. Four series-regulated power supplies are con-
tained in the power supply section. The power sup-
plies provide +225, -6.3, -165, and +25 voltsdc to the
Model 608 Signal Generators. The four supplies are
connected toa common input source through ON switch
83. A slide switch located on the rear panel of the in-
strument sets the generators for use with either a
115-Vac or 230-Vac power source, with AC LINE
fuse FI connected between the power supplies and
source as a protective device. The supplies are illus-
trated in Figure 7 _5 and are described in the follow-
ing paragraphs.
4-65. THE +225 VOLT SUPPLY. Input ac voltage to
the +225-volt supply is received across transformer
4-8
Model 60aE/F
T1. The secondary contains bridge rectifier CRa
through CRll and filter capacitor C40. The supply is
series regulated through triodes V13A, V13B, and
VI6B, with the output connected to the load through
front-panel mounted DC 0. 25 AMP fuse F3. The -165
Volt Power Supply output is used as reference, being
applied through a voltage divider consisting of resis-
tors R70 through R72. Any change in the load is sensed
across +225 Volts Adj potentiometer and applied to the
control grid of Comparison Amplifier V12. The plate
of amplifier V12 controls the conduction level of the
series regulators, and holds the output voltage con-
stant. The +225 volt supply is used to reference the
+25 volt supply discussed in paragraph 4-69.
4-66. THE -6.3 VOLT SUPPLY. Input ac voltage to
the -6.3-volt supply is also received across trans-
former Tl. Rectification and filtering occur across
bridge rectifier CR16 through CR19 and capacitors
C75. Transistor Ql operates as a comparison ampli-
fier and series regulator, with the base circuit ref-
erenced by -7.5 Vdc developed from the -165 Vdc
supply across resistor R260 and Zener diode CR20.
The output voltage of 7.2 Vdc is applied to RFI Filter
FL4 where 0.9 Vdc is dropped. The -6.3 volts is
then used as a filament supply for RF Oscillator V6,
Buffer Amplifier V22", and Power Amplifier va. Fila-
ment voltage for the remaining tubes in the instrument
is prOVided by a separate secondary winding of trans-
former T1. The latter winding also supplies voltage
to a' light behind the MEGACYCLES dial, and to the
AC POWER light located on the front panel. Both
lamps are lighted when switch S3 is in the ON position.
4-67. THE -165 VOLT SUPPLY. Input ac voltage to
the -165 volt supply is received across transformer TI,
and rectified by diodes CR12 through CRI5. Tricxle
V16A is the series regulator, with the grid controlled
by the plate of Comparison Amplifier VB whose cathcxle
is referenced by gas tube v15. The voltage level is
controlled -165 Volts Adj potentiometer R80, with the
output applied to the load and to the +225 and ·6.3 volt
supplies for reference.
4-68. THE +25 VOLT SUPPLY. Components of the
+25 volt supply are located on the Modulator and ALC
Board, which also contains a portion of the Amplitude
Modulation Section circuits discussed in paragraph
4-37. Ac power to the supply is received across trans-
former T2, and rectified by diodes CR29 and CR30.
Transistor Qll is the series regulator, with the con-
duction level being control by Amplifier QlO. The
supply is referenced by +225 Vdc received across
resistor R239.
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