Decca aw 10 service manual

Page 1

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" TRADER SERVICE \SHEET

432

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HESS -_ liU'lTON tuning of tho
Pmechanical type for eight sinuous

(including 3 MW and LVV slation on
each of two buttons) is provided in (hi:
Decca AW 10 receiver.

The receiver is a Swalve (plus recti-
lior) Zi-band superhet, Suitable for ope
lion from M19250 V, 50450 C/S mains.

'llie short-wave range is 16-50 in., and
provision is made for the connection
of a. gruniophone pick-up and a. high im-
pedance external speaker. Two beam
lctrndo Valves are connected in parallel
to iced the two internal loudspeakers,

Supplemem la The Wireless &
Electrical Trader, Our 1

»

DECCA AW IO

PRESS-BUTTON

which are also connected iii

In connection 'h the press-button
unit, it magnetic i ay is fitted to elimi»
mate the manual friction drive, so that
quite n light pressure on the buttons is
sufiicient to turn ihc gang. The opera-
tion of tho relay, which acts automati-
cally, is described in (Tirmuf Drscrip-
lion and Gum'ul Nutcsi

erww (late: August, 1931).
CIRCUIT DESCRIPTION

Aerial input is via coupling condenser
02 and L2 (SW), and L3 (MW and
LW) to singlo tuned circuits L4, (:33
(SW), L5, C33 (LVV) or L6, 033 (MW).

Coupling on MW is quite straight-
forward from L3, while L5 is short-cir-
cuited by switch S4; but on LW,
coupling to L5 is via L3, L6 and 03,
while 82 is closed.

First. valve (VI, Mallard metallised
TH62) is a triode hexode operating as

paralleli

frequency changer with internal
coupling Triode oscillator grid coils
L7 (SV ), L8 (LW) and L9 (MW) are

tuned by C34; parallel trimming by 035
(51V), 011, C36 (LW) and 037 (MW);
series tracking by 03 (SW), c9 (LW)
and (:10 (MV I. Reaction hy anode coils
L10 (via stabi ising resistance R6. SW)
and L11 (MW and LW).

Svcond \alve (V2, Brimar GU76) is a

AC SUPERHET

iableqnu RF pentode operating as
intermediote frequency amplifier with
tuned-primsry tuned-secondary trans
former couplings (:38, L12, L13, C39 and
C40, L14, L15, C41.
Intermediate frequency «65 KC/s.

Diode second detector is part of double
diode triode Valve (V3, Mullard 6076).
Audio frequency component in rectified
output is developed across load resistance
R13 and passed viii 1F stopper resistance
R12, AF coupling condenser (:18 and
manual volume control R14 to CG of
triode section, which operates as audio
frequency ainplitierl IF filtering by R12,
017 and C19. Provision for connection

of grainophoue pickup by sockets
directly across R14.
Control potential to operate the

cathode ray tuning indicator (T,I_.. Mul-
Iard EN), to whose control grid it iS
applied via decoupling circuit R11 and
C16. is obtained from Junction of R12
and R13. The cathode circuit of the tun-
ing indicator, to which the CG resistance
R25 is returned, is returned to V3
cathode circuit.

Second diode of V3, fed from tapping
on L15 via coupling condenser 021,
provides DC potential, which is de-
veloped across load registance R18 and
fed back through decoupling circuits as

R7

SCALE imvs

K9 m

34-

b4-

Page 2

Under-chassis view.
A diagram of the
Sl-59 switch unit
is given overleaf.
Most of the trim-
mers (except those
of the IF trans-
formers) are in-
dicatedf The core
of LI, the IF filter
coil, is adjusted
through a hole in
the rear of the
chassis

GB to FC and IF valves, giving auto-
matic volume control. Delay voltage is
obtained from drop along M5 in V3
cathode lead to chassw. .
Resistance-capacity coupling _l)y R17,
023 and R19 between V3 trion and
parallel connected two~valve output
stage which comprises two beam tetrode
valves (V4, V5, Mullard

LIB

SVSGS). Provision for
connection of high iin-
pedance external speaker
)etween anodes (Via
stabilising resistances
R21 and 322) and HT
positive line. Variable
tone control by R23 zmd
C25 in anodes circuit.

Fixed tone correction
by 026. also in anodes
circuit, b n t returned

directly to chassis

The speech coils L16
and L11 of the two in-
ternal speakers are con-
ted in parallel nor ~

, Circuit diagram of

the Decca AWio.
Note in the cathode

:27:=: cze:==

return circuit of
V4, V5. the relay

winding, which
operates in con-
junction with Slo.

Supplement to The Wireless 4:
Electrical Trader, 01:1. 2.1, 1939

the single internal speaker input trans-
former T1.

The common V4, V5 cathode hissing
rolnponents R20 and 024, together with
lhe common CG resistance R19, are nor-
mally connected to chassis via. switch

$10: but (hi switch. with sw1tch $11,
,pe single-pole changeover
switch unit which is associated with the
mechanical press-button unit. When
one of the buttons is pressed, $11 closes
to mute the speakers. and $10 opens, so
that the cathode current of V4 and V5
flows In chassis through the magnetic
relay}, whose armature is thus attracted.
The application of this device is thence-
lorth entirely mechanical, and is dealt
with under General Notes

HT current is supplied by IHC full-
wave rectifying valve (V6. Brimar
524G). Smoothing is effected by iron-
cored choke L18 and dry electrolytic con-
densers 027 and 028. Mains BF filter-
ing by C29. Fuse F1 affords the input
circuit protection against damage in
case of accidental shortcircuit, while its
niounting acts as the voltage adjustment
it "Hi

. D|SMANTLING THE SET

Before the chassis can he removed. it
will be necessary to remove the
speakers, though some measure of access
may be gained to it through the open»
mg in the chassis supporting shelf.

Removing Speakers. -Unsolder the
speaker leads and remove the eight nuts
[with lock washers) holdng the speakers
to the sub-baffle.

When replacing, see that the smooth-
ing choke on the left-hand speaker faces
the input transformer on the right-hand
speaker when the speakers :lle viewed
trom the brick of the cabinet, and con»
noon the leads as follows. niunbering lhl
fog: on the input iransfmmt'r from top

oECCA
AW I0

432

to bottom: 1, black lead with white
trainer from left»ha,nd speaker together
With black lead from two-core cable: 2,
block lead from three-core cable; 3, blue
lead from three-core cable together with
upper lead from smoothing choke on
left-hand speaker; 4, red lead from
three-core cable together with lower lead
from smoothing choke on left-blind
speaker; 5, red lead from two-core cable
together with other black lead with
white tracer from lefthund speaker.

Removing ChassisiRemove the four
control knobs (recessed b screws},
the six press buttons (pul oil), and the
four bolts (with claw washers) holding
the chassis to its supfporting shelf,
ll'llen replacing, do not orget. to place
:i felt washer between each of the con-
1 WI knobs and the cabinet, except in the
(ilse of the tuning control knob

COMPONENTS AND VALUES

, v i l Value:
RESIsrAMLs (ohm)
in v1 hexode (JG resistance 500,000
R2 v1 hexode (JG decoupling 500,000
, its Vi hexode mid stopper 40
, RA V1 fixed GB resistance 250
, 105 v1 om CG resistance 50,000
i Re One. motion sw damping. 70
in v1 osc. anode HT feed 35,000
as v2 CG decoupling . . 500,000
110 v1. V2 SGs HT feed. . 35,000
1 R10 v2 fixed GB resistance 250
im '1.l. CG decoupling 1,000,000
, 1012 1r stopper 1 70,000
, me vs signal diode load 300,000
; rm | Manual volume con 1 500,000
> ms vs mode GB and AVCdelny
resistance . l 0,000
me vs mode anode decoupling 25,000
m7 v3 mode anode load... 100,000
K18 vs AVG diode load , 500,000
, R19 V4, V5 CG'S resistance l 250.000
1 mo V4, v5 fixed on resistance." i no
, R21 v4 anode stomlei .. l mu
1022 - vs anode stopper . , 100
1 R23 Variable tone contro 50,000
i 1:24 1:1. anode Hr feed i 2,000,000
1:25 ; TI. on resistance 000 000