Electrometers 3 and V4, Circuit Description

m e t e r i n g circuit in the main unit.

coupled to the metering circuit in

(2) Electrometer V4 also functions as

the main unit.

an extremely high input impedance

d. Electrometers 3 and V4, Circuit De-

t r i o d e amplifier. Similar to elec-

s c r i p t i o n . Because of the very high input

trometer V3, the plate (pin 1) and

i m p e d a n c e of the type 5886 electrometer

screen (pin 2) are tied to the com-

t u b e , almost no grid current is drawn by

mon source of plate potential. For

V 3 and V4. Resistor R12 and capacitor

V4, however, the source voltage is

C13 in the grid circuit of electrometer V3

t h r o u g h terminal 4 of J2, which

serve as a filter for the detected if. signal.

c o n n e c t s to the cathode of meter

Capacitor C13 also functions to place the

cathode follower V702B in the main

grid of V3 at low rf potential. An identical

u n i t . The heater circuit of V4 re-

circuit is used at the input to electrometer

ceives 1.2 volts dc, through termi-

stage V4, with R13 and C16 as the if. filter

nals 2 and 3 of J2, from a separate

elements. Capacitor C12, connected to the

rectifier circuit in the main unit

j u n c t i o n of thermal relay heater resistors

power supply. Capacitors C15 and

R14 and R15, bypasses if, currents in the

C18 bypass rf currents in the heater

heater circuit of thermal relays K1 and K2

circuit to chassis ground, and serve

to chassis ground.

t h e same functions as capacitors

C 1 4 and U17 for stage V3. Sim-

( 1 ) Electrometer V3 serves as an ex-

ilarly, R17 is the balancing resistor

tremely high impedance triode am-

for the heater circuit. For this

p l i f i e r . Its screen (pin 2) and its

stage, the detected signal envelope

plate (pin 1) are tied together and

voltage is one-third the amplitude

receive a dc plate potential through

of electrometer V3, since the volt-

t e r m i n a l 10 of receptacle J2 from

a g e divider at the input to meter

t h e cathode of meter cathode fol-

d e t e c t o r V2 divides the incoming

lower V702A in the main unit. The

i f . signal into a ratio of 3 to 1.

h e a t e r circuit of V3 receives 1.2

This detected signal envelope volt-

volts dc through terminals 1 and 9

age (negative with respect to

of J2 from a rectifier circuit in the

g r o u n d ) is taken from the heater

main unit power supply and is re-

t u r n e d to -150 volts dc through

circuit (pin 3) and is applied through

t e r m i n a l 3 of J2 to the metering

R719. Resistor R719 serves as the

circuit in the main unit.

e l e c t r o m e t e r output load and the

e. Signal and Power Paths. Interconnec-

g r i d return of V702A. Capacitors

tions from the output of the detector and

C 1 4 and C17 bypass rf currents

e l e c t r o m e t e r assembly to the main unit

in the heater circuit to chassis

are identical in all four tuning units. Es-

g r o u n d and prevent modulation

s e n t i a l l y , four components comprise the

feedback to the power supply. Re-

i n t e r c o n n e c t i o n system. These are:

s i s t o r R16 is a balancing resistor

(1) A multipin receptacle, J2, which

which is tied across the two heater

i s an integral nonreplaceable part

terminals. The value of R16 is se-

o f the detector and electrometer

l e c t e d in production to counteract

assembly.

variations in heater resistance

(2) A mating multipin connector (P9

w h i c h are inherent in the manu-

for tuning unit 1) which is a sub-

facture of these tubes. The de-

m i n i a t u r e plug-in connector that

t e c t e d signal envelope voltage

m a t e s receptacle J2.

(negative with respect to ground),

(3) A wiring harness which intercon-

which is identical in amplitude with

n e c t s the tuning unit and the de-

the output of meter detector V2A,

t e c t o r and electrometer assembly.

i s taken from the heater circuit

(4) A 2 0 - p i n c o n n e c t o r w h i c h i s

(pin 3). This signal is a p p 1 i e d

m o u n t e d at the rear of the tuning

t h r o u g h terminal 9 of J2 to the