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8att<ry ,·oltagc
is appli,d
to the unit by the operation of the OFF-ON
switch S6.
In
the l'NIA (pomble) version of the equipment this
is
a push
switch which
extends
on
a hanging
lead from the
right
reor
of
the chassis.
It is secured to the bottom of the use n<ar the
right
edge, so as to
be
within
easy reach of
the
operator when he is carrying the unit. In the
PN1B
(fixed
station) ,.,rsion S6 is
a
standard
toggl<
type switch, and is
mounted
at the
low« left hand comer of the front panel next to the C.\'v'.-PHONE switch.
When the OFF-ON switch is placed
in the "ON" position,
connections are
made to the transmittec,rteeiver
circuit,
from the "A" positive, and
from
the
combined
"A" and
"B"
negative lead, of the batteries.
The voltages dcliYer<d by the
batteri:s
arc
180
volts, with
a
tap at I})
Yolts,
foe
the "B" supply, and three
volts
for
the "A"
supply. The recei,-cc
,·alves require 1.4
lo
I.)
volts for each nl1mcnt, and are connected in a series
par>llel
arrangement
across the ; volt source.
A
rheostat is employed to reduce
the supply to between 2 0 and 2.1 volts for the transmitter valves. This
rheostat
is
mounted on the front panel, where its control is designated
"Fil.".
The fli!lh tension
required
for the receiver is approximately
90
volts and is
obtained throu!(h the dropping resistor
R31
suitably
bypassed
by
the electro-
lytic condenser C26.
Mount<d in the center of the chassis is a telephone type relay which
is
oper.1ted from the 3 volt supply circuit
through
either the SEND-RECEIVE
switch on the panel, or the "Press-to-Talk" switch on the microphone. It
transfers the 3 volt supply from the receiver valve, to the transmitter vahcs,
:i.nd also tr.insfcrs the ancenna from the receiver to the tr.1.nsmitter.
The
receiver
section occupies the left-hand portion of
the
combined
chassis. It
ublius six vah·eJ in
a.
superheterodync
circuit
performing: nine
functions,
as
follows.
The r.( amplifier us,s •
type
IP5GT/G pentode valve. Th~ .J!rid of this
valve
receives the
incomin.l(
si}!nal from
the
tuned grid winding of tht r-f tr>ns-
former Tl. The base of this winding is connected through
Rt
to
the
·
a utomatic volume control circuits,
the
tuned
circuit bein~ completed
through
the
.Ol
uf. condenser Cl. The antenn• windin11 of Tl
is
of
high
impedenct
and m•tches tither the wire or
the
rod antenna. The plate
of
the I P,GT/G is
connected through
the primary winding of the
detector
transformec T2
to
the
m:un 90
,·olt
high tension
supply.
The detector-oscillator or converter valve is a type
I A
7G'f/G which
performs
the
double
function of o
frequency-_changing
rectifier and high
frequency oscillator. A1:ross its signal grid ,re imoressed
the
incoming
r-f
signals,
"hich
h1ve been selected and ampli~cd b)' rhe
r-f
and
detector
trans-
formers and the
r-f
amplifier valve. The triode portion of the converter yalve
i,
used
for the
high-frequency
l)Scillator
and
is shunt-fed;
the •node
grid
receivin.1t its 1•oltage from the
90
,olt supply throuRh the
droppin~
raistor
R).
The
oscillator
transformer
T3 pro,-ides pJ.te-to
~rid
coupling,
•nd
grid tuning,
and the
grid
tank
circuit is normally tuned
10
a
frCQuency 455 kilocycles
hiJ?hec
than the
r-f signals.
The oscillations
set up
arc fed through the grid coupling
3
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