Decca 33 service manual

Page 1

ll (Supplement)

TRADER SERVICE SHEET 1

24-7

SHORT~WAVE range of 19-49
Ametres is included in the Decca 33

3»valve battery»operated receiverl
There is provision {or both a gramophone
pick-up and an extension speaker.

CIRCUIT DESCRIPTION

Aerial Input via coupling coil L1'(SiW.),
L2 (M.W.) and L3 (L.Wl) to single tuned
circuits L4, 013 (S.VV.), L5, 016 (MiW,)
and L6, (116 (L.W.), which precede first
valve (V1, Tungsrlnn metallised vpzs), a
variable-mu pentode operating as R.F.
amplifier with gain control by potentio-
meter R2, which varies G.B. applied.

Tuned anode coupling by L10, 021
(S.W.), L11, 021 (M.W.) and L12, 021
([..W.) between V1 iuid detector vaIve
(V2. Mullard metallised SP2), an RF.
pentode operating on the grid leak
system with R4 and 05. Reaction is
applied Iroln anode by coils L7 (S.W.),

THE WIRELESS & ELECTRICAL TRADER

September 18, 1937

DECCA 33

3-BAND BATTERY RECEIVER

COMPONENTS AND VALUES

RESISTANCES

reSIstance

R1 Vi ain control

R3 Vi I; and anode HIT'. runl' '

R4 vi grid leak

R5 V1 Gila, filament potential-i
no meter .. ..

R7 Vzanorlelozidrcsist. me ..
fig }Pnrisol V2 anode R.l~. film 1
RH) vac resistance

Rn V3C .k. qoppu

R12 V3alltonmi .

b s condensers

o' I iii to. ginningnni iii?

I

Values
(olmisl

20,000
600,000
10,000
1,000,000
loo

l .000
100,000
10,000
59,000
300.000

l no.ooo
son

Approxi
OTHER (OMION .MS Values
(ohms)
Aerm sw. rouplng 0-3
L2 Aerial M,w. oonpling -0
L3 AcrialLW coupling . 73o
L. . tuning coil Very low
L5 w. timing coil 5~o
L6 Aorinll w. tuning mil 17-0
1.7 on coil 0-5
Ls M.W4rr>a iononii .. 04
Lo LW. roactiontoil .. ., 4'0
[.10 V! anode sw. tuning mil .. o-i
Lu VI anode MW tuning coil ,. 3-:
Liz vi anode L.w, tuning mil .. 261)
L13 Spenkerspeoch (oil I.) . r8
. . , , n. 1350-0
1': Spealirr input Irons. [Sm M
SLSIB anebaud switches . .. - ~
519 L.T. circuit switch ,. ,. c.

DISMANTLING THE SET
A detachable bottom is fitted to the
cabinet and upon removal ( x counter-
sunk»head wood screws) gives access to
most of the components beneath the

C3 vi mlmiodeRJ . I) was; o-oi
Ls (M.W.) and L9 (LAM), and controlled 94 vi 5 . and anode not-Joint; o olins.
by 020. R.F. filtering in anode circuit by 2% $2 t? coudeliier .. 030005 Removing Chassisnwlf it should prove
R.C. network R8, 07, R9 and 08. c7 l 2 "WWW; ", 3,00 necessary to remove the chassis from the
Resistancercapauty coupling by R7, til i :1": W V fmie [1" mi iyoooi cabinet, remove the {our control knobs
C9 and R10 via R R stopper 311, t9 , my yg."-I-*P|{ilfb 0}? (recessed grub screws) and the two bolts
between V2 and peutode output valve ci? H,r?';gs;:voir;;;§f;,se,y 53;, (with washers and lock-washers) holding
(V3, Mullard PM22D). Provision for con- on v. Anodp fused tone poll-enter 0'00 the chassis to the bottom of the cabinet.
nection of gramophone pick-up across EU: IA fl: C3:."ayv '{:E""';: , ' The chassis can now be withdrawn to the
R10 in C.G. circuit. GiB. vo tage for CE: "'71 ziinIt L'wjmglxcf extent of the leads which is suflicient for
V8 is obtained from drop across resistance Czcy tuning _ .. normal purposes.
312 in H.1. negative lead. Fixed tone 3g; ffi'vvi'i i'w'iifi' " When replacing, note that one of the
correction in anode circuit by 012. 59: "m " knobs is fitted with a sleeve This should
Provision for connection 01 hi h C2 Reaction (rooms be laced on the swindle oi the reaction
. g , I7 I
impedance external speaker across the CHI AW? 10" mmg .. ' control.
primary of T1. 'Electmlyiic, rvilriaiile tIrchl. To free the chassis entirely, linsolder
RED LIT .2
m N
A BLUE H r. ~I
in
R9
=< 9
{.
4 L4 I 37
[I
ficu 54
-
31 U I KB
L2 E
04 (55
53 P U =CI Z
L5 l 59 T
I.) g .
Q; {So BULK m ,
.I; .I. all
CIT CIT t Imo "9 on i
BLACK LT _
RED
l T .
I I 5 BLACK GB. _

Circuit diagram of the Decca 33 3-band battery receiverl

Page 2

September I 8, 1937

Plan view of
the chassis.
Note the mark-
ings for the
various leads
which emerge.

the leads from the speaker and remove the
panel carrying the aerial, earth and pick«
up Sockets (two roundvhead wood screws).

Removing Speakerle-To remove the
speaker from the cabinet, unsolder the,
leads coming from the chassis and exten-
sion speaker socket panel and remove the
nuts from the tour screws holding it to
the Suki-baffle. When replacing, see that
the transformer is at the'top.

VALVE ANALYSIS

Valve voltages and currents given in
the tahle below are those measured in our
receiver when it was operating with an
tiff. battery reading 123 V on load. and
with the H.[.-(» I plug in the no V socket,

The receiver was tuned to the lowest
wavelength on the medium band and the
volume control was at maximum, but the
reaction control was at minimum, There
was no signal input.

Voltages were measured on the 1,200 V

scale of an Avometer, chassis being
negative.
I Anode Anode Screen Screen
l Valve Voltage Current Voltage Current
(V) (an) (V) (lnA)
VI VI2B 100 l 3 mo 0-4
V2 SP2 55 0-4 60 0-!
V3 l'ltml) no 2 7 [23 l 0'4

GENERAL NOTES

Switches.ksl-518 are the waveband
switches, in two rotary units beneath the
chassis. These are indicated in our under,
chassis view, and shown in detail in the
diagrams on this page. Note that the
first unit is viewed from the front: of the
chassis, and the second from the rear.

The table below gives the switch

Switch M .W.
, C
C W _
C C .
G . C
, C C
m C
a ,
C
' 0
C
C .
C 0
C C
0 0
- C
C
0 ._

THE WIRELESS & ELECTRICAL

positions for the three control settings,
starting from fully anti~clockwise A
daSh indicates open, and 0, closed.

819 is the QJVLB. l..'l. circuit switch,
ganged with the gain control R2.

00ils.~-All the coils are included in
pairs in six nnscrecned units, wound on
tubular formers beneath the chassis.
These are indicated in our underichassis

Switch dia- ,
1 grams, looking ,
: in the direc- :

(ions of the

arrows in the >

under-chassis I

view.

TRADER

(S upplemem) II I

view. Each unit has its associated
trimmer fittedat the end of its former.

External Speaker.-Two sockets are
provided on a small panel at the top of
the bank of the cabinet for a high
impedance (about 20,000 0) external
speaker.

Batteries.#L.T., 2 V accumulator cell ;
H,T., r20 V H.T. battery; 013., )5 V
CB. battery, The HIT, battery should
not exceed 8; in. by 7 in. by 3 in. in size.

Battery Leads and Voltages.~Blacl<
lead, spade tag, L.Ti negative; red lead,
spade tag, LT. positive 2 V ; black lead
and plug. HT. negative: blue lead and
plug, H.T. positive 1, +60 or +80\':
rod lead and plug, Hfl. positive 2,
+120 V: short rod lead and plug, GB.
positive; short black lead and plug,
G.B, negative, 7-12 V.

Bearer PlatQSrTwo paxolin plates
fitted inside the back of the chassis, and
provided with tags, serve to carry a
number of connections.

A and E Connections.~'lhe aerial lead
(brown-yellow) and the earth lead (blach)
from the chassis go to two sockets on a
paxolin panel at the top of the back at the
chassis.

CIRCUIT ALIGNMENT

When the gang is at maximum the
pointer Should cover the right-hand
horizontal lines on the scale. plate.

Connect a signal generator to A and E
sockets or leads. Turn volume control to
maximum, and reaction control to a
point just short of oscillation Switch set
to L.VV., tune to 1,700 m. on scale. feed in
a 1,200 mi (250 KC/S) signal, and adjust
019 and 015 (or maximum output.
keeping set just short of oscillation.

Switch set to M.W.. tune to 220 m. on
scale, feed in a 220 m. (L360 KC/S)
signal, and adjust 018 and (114 for
maximum output, keeping set just short
of oscillation.

Switch set to S.W., tune to 20 m. on
scale, feed in a 20 m. (15 MC/S) signal, and
adjust 017 and 013 {or maximum output,
again keeping set just short of oscillation.

Under-,chassis view. Note the six coil units and their trimmers.