HP 120A - Page 50

DIAGRAM NOTES
Heavy solid line shows main signal path; heavy dashed line shows control, secondary signal,
or feedback path.
Heavy box indicates front-panel engraving; light box indicates chassis marking.
Arrows on potentiometers indicate clockwise rotation as viewed from the round shaft end, counter 
clockwise from the rectangular shaft end.
Resistance values in ohms, inductance in microhenries, and capacitance in micromicrofarads
unless otherwise specified.
Rotary switch schematics are electrical representations; for exact switching details refer to
the switch assembly drawings.
Relays shown in condition prevailing during normal instrument operation.
t indicates a selected part. See parts list.
Interconnecting parts and assemblies are shown on cable diagram.
VOLTAGE AND RESISTANCE DIAGRAM NOTES
Each tube socket terminal is numbered and lettered to indicate the tube element and pin number,
as follows:
♦
=
no tube element
P
-
plate
H
=
heater
T
=
target (plate)
K
=
cathode
R
=
reflector or repeller
G
=
control grid A
=
anode (plate)
Sc
=
screen grid
S
=
spade
Sp
=
suppressor grid Sh
=
shield
Hm
=
heater mid-tap
NC
no external connection to socket
Is
=
internal shield A
=
indefinite reading due to circuit (see 2.)
The numerical subscript to tube-element designators indicates the section of a multiple-section
tube; the letter subscript to tube-element designators indicates the functional difference between
like elements in the same tube section, such as t for triode and p for pentode.
A socket terminal with an asterisk may be used as a tie point and may have a voltage and
resistance shown.
Voltages values shown are for guidance; values may vary from those shown due to tube aging or
normal differences between instruments. Resistance values may vary considerably from those
shown when the circuit contains potentiometers, crystal diodes, or electrolytic capacitors.
Voltage measured at the terminal is shown above the line, resistance below the line; measure 
ments made with an electronic multimeter, from terminal to chassis ground unless otherwise
noted.
A solid line between socket terminals indicates a connection external to the tube between the
terminals; a dotted line between terminals indicates a connection inside the tube. Voltage and
resistance are given at only one of the two joined terminals.