Decca deccette service manual

Page 1

[All'riflite reserved. This service date sheet is the copy-
right 0! Wmuss a Eucnlcu. Tum and may not
be reproduced, in whole or in part, without permission.)

TRADE! SERVICE SHEET

1113*

N unconventional internal aerial,
comprising two coils wound on an
iron-dust rod, is used in the Decca

. Deccette, a. four-valve portable super-
het operating from ell-dry batteries.

A se arete mains unit has been de-
signed or use with the Doceette, and
enables it to opente from 200-250 V A.C.
msins of 50 c/ s.

When the receiver is operated in con-
junction with the mains unit the internal
batteries are automatically disconnected,
and the receiver may be switched on and
03 from the mains unit without using
the volume control on/ofl switchi

Although the receiver is a single-wave-
hand model, covering the M.W. range of
200-600 In, provision is made for the
reception of the L.Wl Droitwich trans-
mission. The pre-tuned L.W. circuits are
brought into operation by tuning the
receiver past the low-wavelength end of
the M.W. band to the Droitwich set-
ting on the tuning scale.

Release dates and original prices:
Deccette, July 1953, £12 135 7d, plus
purchase Mar; Mains Unit, [uly 1953.
£5 5s-

The appearance of the mains unit showing
the connector plug on top and the on/ofl
switch at the side.

CIRCUIT DESCRIPTION

The aerial input ooils L1 (M.W.) and
L2 (Pro-set L.W.) are mounted at oppo-
site ends of a length of ferrite rod to
form the internal aerial, and are tuned by
026. Tuning the receiver to the Droit-
wich setting on the tuning scale (gang at
minimum capacitance) automatically
opens switch 31 (operated by the drive
drum) bringing the L.W. pre~tuned cir»
cuit L2, 01, 021 into operation.

Heptode valve (V1, Otrlrn X11) operates
as frequency changer with electron
coupling. Oscillator coil L3 is tuned by
(:21. Parallel trimming by 028 and series
tracking by 01. In the L.W. pro-tuned
position 32 closes, shunting 08, (:29
across the grid circuit. Inductive reaction
coupling between the two halves of L5.

Supplement :1
Electrical Trade!

DECCA - [

All-dry Battery Portable l
contained Mains Uni

Second valve (V2. Osram W11) is a
variablemu R..F. pentode operating as
intermediate frequency amplifier with
tuned transformer couplings 03, Lt, L5,
0 and 010, L6, L1, 011.

Intermedllte frequency A12kc/ c.

Diode signal detector is part of diode
pentode valve (V3, 0mm 1011). Audio-
i'requency component in rectified output
is developed across volume control RB,
which operates as diode load, and essed
via an to control grid of polite e sec-
tion, which operates as A.F. amplifier.
LF. filtering by on, Its, 013 and on.

DC. potential developed across R5,
R6 is fed back as bias via decoupling
circuit R4, cs to V1 and V2 giving auto-
matic gain control.

Resistance-capacitance coupling vie
R8, 018 and R12 between V3 and pentode
output valve (V4, Otnm N19). Tone cor-
rection by 018 in the anode circuit and by
the negative feed-hack between V3 and
VI anodes via R10. Grid bias voltage for
V! is developed across R11 in the H.T.
negative lead.

Internal aerial
assembly

C2
' ll

C RI
26 27

TCS

E

M
5
$53
in 625 a
1:} L1 L3 '
ll: co

m _
m T- .

m

m C7

c

R3

R7 7

F L63 cu

Cl 0
L7

R5

R8

C

29 I528 CI2_ as
J R4

8

52

I

C9

[

1

CM

R6

1
1R9

05

cm: an

T_-,

Circuit diaéram of the Decca Deccette. Switches 81 and 82 are operated by the gang drive drum and bring the pro-tuned L.

The right-hand section of the circuit shows the A.C. mains unit.

The connections to the mains unit socket in the base of ti:

Page 2

to Wireless {9
',Se)>tanber26, 1953

DECCETTE"

using a Detachable Self-
riit for AC. Operation

The receiver, which is designed
primarily for operation from 9.11- dry
battefies, may be powered from an A. C.
mains supply by means of a. separate add
on mains unit. When in use this mains
unit forms a. base on which the receiver
stands, H.T. and L.T. connections be-
tween the two being made by a four- -con-
tact plug on top of the unit and a. cor-
responding socket in the base of the re-
ce1ver (this socket is closed by a rubber
plug when not in use). A small plastic
peg on the end of the mains unit con-
nector plug operate: switches 83, SA in
the receiver, disconnecting the internal
batteries. A slidetype on-ofi switch is
fitted to the side of the mains unit.

For mains operation HUT current is
supplied by half wave metal rectifier
(MRI, Westinghouse 11129). Smoothing by
613, R13 and 010, the latter being located
on the receiver chassis and for battery
operation functioning as the normal H.T.
battery by-pass capacitor. L.T. current
is supplied by full-wave metal rectifier
(MR2, Westinghouse 16K1). Smoothing by

-.g--pHJZ4

The appearance of the Decca Dcccette
portable superhet battery receiver. Its
associated mains unit is shown in col. 2.

choke L8 and electrolytic capacitor: 021,
012. The two halves of V4 filament are
connected in parallel for 1.4V operation,
and together with the filaments of the
remaining valves are parallel-fed for both
mains and battery operation.

The six leads connecting the receiver
chassis to the mains unit socket on the
underside of the carrying case are colour
coded in the circuit diagram and refer
to the coloured lead terminations shown
at the foot of column 3 overleaf.

LW. station circuits into operation when the gang is tuned to minimum capacitance.
the receiver are shown in detail in the drawing at the foot of column 3 overleaf.

DECCA
DECCETTE "

11.13

COMPONENTS AND VALUES .

CAPACITORS Values Loom
tlons
Cl LNV. aerinltrim ldOpF Cl
0210 G OODF A2
03 list I. F trans 65131 A1
C4 85pF A]. i
05 A. 6.0. decoupling 004151? 32 1
C6 Vlow .CG. 1001)? A2 1
C7 Osc tracker 5651)]? E4 1
CB L.W. oscillatortflm. 0 004MF E4 .
09 V2 8.6. decoupling ONE? 32 1
8:? 2nd I.F.ttrnne. E; 1
nnlng .
012 B2 1
018 LEW-passes D3 .
014 A3. coupling D4 .
015 V3 5.61. decoupling 0 04uF D4 1
010 I.F.b -pass BZ 1
(117° G.B.rleeoupling D4 1
018 A. F. coupling (12 1
019 Tone eorrector E3 1
020 Battery reserve D3 1
021 Filament (35 1
022 smoothing Ga
023 FLT. reservoir G5 1
C24: L.W. aerialtnue F3 1
C25: M.W. aerial trim F4
026? Aerialtunlng E3
0271' Dillatol'tuninl E3 1
029: M.W.osc.trlm 1n 1
029: I. W. are. tune B2 1
. . __1
' Electrolytic. r Variable. 1 Pro-let.
_4 _ ___. . if 1 i
BESISTORS Values Loca-
tlom

1 1p 1
1 OTHER COMPONENTS 1 \lhlucs 113:)";
1 (oh ms) 1
1_'_- .

1 i; 1}Internnlaerinlcoils{11_g 1322 1
l1: Oscillatorcoil .._. 1 1:3 ' £2 1
L5 1 lstI F. trans. ,0 A1
£2 1 2ndI.F. trans. fig 1% 1
L8 1 Speech toil 2-s - 1

. L9 1 L. T smoothing 1 1

1 1 choke 1 so G51
r1 1 0.P.tram. 5;; : 30 1E3

121 1 $33 1 cs
. .890 1
T2 1 3:11; L.T.see. 1 . 1 1
1 ~ total . 1-8 1 1
Pllotsec. > 20 1
81,521 L.W.pre-setsw . - Bl
s4; Malns/batt.sw. -- 11m
561 ' 1 - E3
1 - 1 G5
- 1 as 1

Dealers are reminded that the
component numbers used in the
above tables may be different from
those used in the makers' circuit
diagram. If any component num-
bers are used, therefore, when
ordering spares, it is advisable to
mention the fact on the order.