Decca aw 6 service manual

Page 1

TRADER SERVICE SHEET

4|8

The Decca AW6 receiver.

HE Decca AW6 IS a 4-valve (plus
rectifier) AC 37band superhet, suit~

able for mains of 200-250 V,
50760 CS. The SW range is from 12-32 n1.
There is provision for a high impedance
external speaker, and for a gramophone
pick-up, a gram. position being provided

on the wavechange switch. An IF filter
and a 261 m rejector (on LW) are
incorporated.

Release date : February, 1939.

CIRCUIT DESCRIPTION

Aerial input via series condenser 02
and coupling coils L3 (SW), L4 (MW)
and L5 (L\V) to single~tuned circuits
L6, 083 (SW), L7, (:33 (MW) and L3,
033 (LW). IF filtering by L1, 01 across
aerial circuit. Rejector circuit L2, 03,
connected in series with LVV coupling

Supplement to T he Wireless &
Electrical Trader. July 29, 1939

DECCA AW6

3-BAND AC SUPERHET

coil, is tuned to 261 m to prevent MW
break-through on LW band.

First valve (V1, Mullard metallised
T362) is a triode hexode operating as
frequency changer with internal coupling.
Triode oscillator grid coils L9 (SW),
L10 (MW) and L11 (LW) are tuned by
034. Parallel trimming by 037 (SW),
010, 038 (MW) and (111, 039 (LW);
series tracking by 08 (SW), .09, 035
(M\V) and C36 (LVV). Reaction by
coils L12 (SW), L13 (MW) and L14 (LW).
On SW, (112 and L15 are connected
across the reaction circuit to maintain a
constant oscillator efficiency throughout
the band.

Second valve (V2, Brimnr 61176) is a
variablevmu RF pentode operating as
intermediate frequency amplifier with
tuned-primary tuned-secondary tranSr
former couplings 040, L16, L17, C41
and 042, L18, L19, 043.

Intermediate frequency 465 KO/S.

Diode second detector is part oi
double diode triode valve (V3, Mullaid
6Q7G). Audio frequency component in
rectified output is developed across load
resistance R11 and passed via IF stopper
resistance R10, AF coupling condenser
019, switch 823 and manual volume
control R12 to CG of triode section,
which operates as AF amplifier. IF
filtering by 017, R10 and (218. Provision
for the connection of a gramophone
pickrup via switch S24 across 312:
when the waveband control is turned to
the gramophone position, S24 closes.
while 823 opens to mute radio.

Second diode of V3, fed from a tapping

on L19, Via 021, provides DC potential
which is developed across load resistance
R16 and led back through decoupling
circuits as GB to FC and IF valves,
giving automatic volume control. Delay
voltage, together with GB for triode
section is obtained from drop along
resistance R13, which is connected in the
cathode circuit of V3.

Resistance-capacity coupling by R15,
023 and 317 between V3 triode and
beam tetrode output valve (V4, Mullal'd
BVGG). Fixed tone correction by 025 in
anode circuit. Variable tone control by
R20, 028, also in anode circuit. Pro-
vision for connection of external speaker
between anode and HT positive line.

HT Current is supplied by IHC full-
wave rectifying valve (V5, Brimar 524G).
Smoothing is effected by speaker field
L22 and dry electrolytic condensers 027
and 028. Mains RF filtering by C29.
Fuse F1, which is located in the voltage
adjustment plug, performs the dual
functions of voltage adjustment con-
nection and mains circuit fuse.

DISMANTLING THE SET

The cabinet is fitted with a detach-
able bottom, upon removal of which
access may be gained to the underside
of the chassis.

Removing Chassis.~1f it should be
necessary to remove the chassis from
the cabinet, remove the {our control
knobs (recessed grub screws) from the
front of the cabinet, and the four bolts
(with lock-washers andclaw washers)
holding the chassis to the bottom of the
cabinet, when the chassis may be with-

scns wmwox imp;
AAMPS

sw nw w
W

x5 R8

Circuit diagram of the Decca AW5 receiver.

L1, 01 form an aerial circuit IF filter, and L2, 03
aMW reiector tuned to 261 m. F1,the mains circuit fuse, forms part of the voltage adjustment plug.

Page 2

Supp/mm m The WireIe:: & 4 I DECCA
Electrical Trader, July 29, 1939

AW6

Under-chassis
view. The RF
and oscillator
trimmers are
shown mounted
at the ends of
their respective
coil units. 012
is mounted in-
side the L9,L12,
L15 unit. The
three switch
units are indi-
cated by num-
bers in circles,
and the arrows
show the direc-
tions in which
they are viewed
in the diagrams
overleaf.

drawn to the extent of the speaker leads, Anode Anodc 5mm l V
\VlnCh )3 sufficient {or normal purposes. \nlre Voltage Current Voltage Current kESlsTAXCEs 11::er
To free the chassis entirely, unsolder (Vi in) (V) A) 7,, ,.._._ 7, ,fi,, ,fiW. .
the three leads from the paxolin cone "7" ' {280 2.0 ' 777 Rr Vihexodegif resistance 500,000
meeting strip on the speaker transformer \"r 11-10: 1 Cam laklr } m 2, E2 . ill hefgélebttrélecollplrirg 500,03:
- V n 3 , 1 u | . r.
WM" Veplamng, "5 that the 0 We" V76L7G 1;; g: m 2.7 k. Vr nwrlollrsslstanco ,. 300
control knobs are those With flattened \r; 6070 g 0.85 __ 7 k5 Vin CGres Kuulcé .. 50,000
sides, while the two inner ones are vi 6V0 circular; a felt washer should be fitted V5 5er 2 27 A- 7 7 R; V: gag'figgmy ;; 53:33:;
to each control spindle, between the rgflthmmdfirc R0 V2 fixed GB resistance .. '300
knob and the cabinet; and the speaker gm {Fsgopplerr d'lonl" .. $3333
,, n gslgxla (lo 0 r .. ,
leads should be connected as Iollwsl COMPONENTS AND VALUES R12 Manual volume control 500,000
numbering from bottom to top: 1, no R13 V3triude GB: AVC delay 3,000
connection; 2, red from chas . and red com}.- S R5 Values R14 \(31110de anode lclett-Iurllmg 25.000
from speaker; 3, no connection ; 4, fl _7777 liL_ git: l}; KQYElEiAEeIOSi $323:
black; 5. blue Irom chassis and blue Ct Aerial IF . 000000 R17 V4 cc. resistance .. .. 25 .000
from s eaker. C2 Aerial wmdeuser ,. l 0000.); R18 v4 GB rosisln 00 .. ., Mo
p C3 LW Jena] 201m rejeclor , kl V4llno . . 9 .
Removing Speaket.7$hould it be 'tuuing p. ., .. l 0-0000 R20 Yarmbletone control .. 50,000
desired to remove the speaker from the l; 2:33: C((i 3335,33,; " 3233
cabinet, unsolder the three connecting chailxo mums :: , 01
leads from the panel on the speaker Vinsocgmndenser .. l 000006 , ,4,me
transformer and remove the four hexagon 050, Circultswfimm - r °'°°5 OTHER COMPOXENTS Values
. . 050 Circuit M fixed tracker , 0-0003 (ohms)
nuts (w-th loclrwashersl holding the 0- mmnwnrernnmr mm H-
rlm~oi the speaker frame to the sub- Osc ircuitLWfiXedlrin-imer l 000000 Ll Aeriaumem 35
baffle, when the speaker may be with- {WWWMoweqmliivr 0-0000 L2 1 LWaerlalzsrmrere'c'mrco'li 555
drawn 7 C- amd? 5°leg . - 000: L3 l Aerial SW coupling coil 0:
' , CG dewl"€ -» ~- 0 L4 AerialMWcoupling coil .. 14~o
When replatmg, see that the trans ¥1,V2!Sg'sbdecr)ilplliig .. 0-! L5 , :criale coupling 00 .. 75 o
-. - '2calio e y~pass .. . 0-: - l - ~ - v *
iormer is on the right of the speaker and b d 0-0001 {:5 l fielaifiiilvtihnrling ccoolill .. i ely'éOM
connect the leads as indicated above. 11 Y-Pass w sums 0.00 L; 1 km; i_w (uningmn r 1;.0
AF conplingto Vgtriode ., 0-02 h 0' » - - ' l r ,
- ) s0. EIrCullbW tuning coil , Very 0n
VALVE ANALYSIS V3 39 we d°°°uplg- » 40 1.10 050 circuit MW tuning Coll l 2-5
Coupling to V3 AVC diode .. . 0-000r . o 0 c. c n Lw mm" co .0
Valve voltages and currents given in the \{3 cathode b."P35§ , - 50-0 ii; 1 0:511:50: sw rcactiong its
table (col. 5) are those measured in our 1/; égflifdzobzfp: coupling ngg In; 3 Oscillator MW reaction (,7
receiver when it was operating on mains Fixedtong c5mcgmj :: 0.0, E: , gilgfikhgififggguwr :2
of 230 \, using the 220-230 V tapping on Part of variable tone control 0-05 L15 lF Pi :: 3.5
the mains transformer. The receiver was EHT snnolhing condensers ., f is: L17 i 5' "05' l Seq. .. l 35
tuned to- the lowest wavelength on the Mains RF bypass .. r 0.006 11:;3 rind: "an; 1,5; tom 8::
MW band, and the volume control was at Aerial circulLSW trimmer ,. - L23 Speaker Speech c0 _j _ _ ,:7
maximum, but there was no signal input. 2:232:31: wivgflgg: : sz i Hum neutralising coil . o~x5
Volta es were measured on the 400 V vim , , " _ £22 ; Speaker .59 0°" ~~ ~ 2°?
g , fiend rcuwunmgv, lx bpsakerlnput Prl. ., 350~u
scale of a model 7 Universal Avometer, Oscillatorsclrcnntuning - ("54 {Sea .. 0.1
Chassis being negative. C35: Osc. Clrcult MW tracker f Pri, total _ . 34.0
If valve ada tors are used to connect C36; OSC'Cimmeimfler 7 72 i am l Hem 59° -' °"
, P . C37: 05m CEWW SW "Ynm" 7 1 trans. Reel. heal. see. . 01
the meter into circult for current measurer C38: . Osc, circuit MW trimmer ~ [ HT sec total _ . 530.0
merits, care should be taken to see that 2433; zlcilglcrgiislxtiiirfl? - Sx-Szz Waveband swltcheSH u .. _
, v x .- r t . 7 s: ,2 Radio ramchangeswnc es -
the \ahe screen 1:. sllpped oxer V2 and C: m. tmnssccmmlpg 7 823-2 Indica/tgoflam witches 7
5 7 P
earthed while the anode and screen C42: r 2nd lF trans. pn. tuning .. - 5:8 Mamswmh'ganged R . ._
currents are being observed, as otherwise C43: l 2"! IF a"; 53- '"g H * Fr Mains circuiuuse -
instability may occur. . Electrolytic. vvarlable. : Preset.