HP 400D Operating And Servicing Manual page 18

m
Sect. Page 4
diode CR 1 is non-conducting, as capacitor C32 dis­
charges, current flows through the meter and diode
CR2 to the generator. As capacitor C33 discharges,
current flows through CR2 to the generator.
of
action capacitors C32 and C33 results in the flow
of an alternating current
phased that It ls negative in effect with respect to
the signal on the grid of V2. Capacitor C34 across
the meter integrates the ac component.
3-4 POWER SUPPLY
The powQr supply circuits provide a high-voltage
regulated dc for the plate circuits of tubes VI to
V5 and a low-voltage unregulated dc for the filament
circuits of tubes VI to V4. The filament circuits of
vS
tubes V5 to are supplied directly with 6. 3-volt
ac from windings in the secondary of power trans­
former T l .
a. Input Circuit
The primary windings
may connected for operation from either a 115 volt
be
The
in
the feedback loop, so
of
power transformer T1
(± 10%) or a 230 volt (± 10%) 50/1000 cps source.
The primary circuit is fused. When switch 82 is
in
the ON position, power from the line is applied
to the primary winding of transformer Tl.
b.
by V6, and regulated
trol voltage is supplied to grId
section of VB. The triode section of VB acts as a
dc cathode follower driving the pentode section.
Noise from reference tube Vg is eliminated by low­
pass filter R63 and C35.
Dc drift due to changes
canceled by differential action between the two
sections of VB.
c. Filament Supply
Current for the low-voltage dc filament supply
is rectified by selenium rectifier SRI
by capacitors C39A and C39E. Variable resistor
H66provtdes a means of adjusting the filament voltage.
triode Amplified con­
of
V7 by the pentode
in
VB filament voltage is
and is
filtered