Decca 99 service manual

Page 1

ii Wireless Retailer and Broadcaster (Supplement)

DECCA 99
BAND SIX

[RGUIT.-The aerial is coupled to the
grid of V1, an H.F. pentode operat-
ing as an H.F. amplifier, via a set

of tuned aerial coils. V1 is tuned anode
coupled to V2, a. tliode~hexode trequency
changer, that converts the incoming signal
to a lrequeucy of 456 lies.

The converted signal then passes via an
1.13. transformer to V3, another H.F.
pentode and the IF. amplifying stage of
the receiver. A further I.F. transformer
couples VS to the demodulating diode of
V4, a double diode valve. The other diode
of V4, fed by a coupling condenser, pro-
vides a DC. potential that is utilised by
being fed back to give automatic volume
control.

The coupling arrangements to the grid
of V5, an output pentode, include a
manual volume control. In the anode
circuit of V5 is connected the speaker

of the valve and cathode.

V6, electrolytic smoothing con

coil).
underside of the chassis.

front.

enables the larger knob in be. pulled off.

Uncleat the speaker cable.

cable.

FOUR-

bo removed if required, or, alternatively,
the leads to the speaker panel unsoldered.
For the reverse proces the blue lead is
connected to the lowest tag, the black
lead to the one above it, and the red lead
to the second tag from the top,

Special: Notes-The receiver has six
pilot lights, all rated at 6 volts .5 amp.

The mains voltage ndjiistment device
located at the rear of the chassis takes
the form of three sockets, marked with
respect to the voltage toppings, and a con-
nector that contains a fuse. If the fuse
should blow, then this may be replaced by
unscrewing the two metal connectors and
feedin one-amp. fuse wire through the
small liole provided.

A pair of sockets at the rear of the
chassis enable a. pick-up to be connected.
Either a crystal or high impedance pick-up

October 23, 1937

A lull-vision scale illuminated in

sections according to the setting of

the wave change switch is a ieaiure
of the Decca 99.

CON DEN SERS

. . should be used. Purpos
matching transformer and alsoa variable A similar pair of sockets enable an -h"_'-
resistance and condenser in series to pro- 1 A.V.C. decoupling .1
rule tone controL A pentnde compensator _ 2 Grid blocking . ., ., .00005
condenser is connected between the anode RESISTANCES i X} iqgeeélefclecmllplingu .. -;i
l s oupmg .
. . . . 5 MW. fixed pad .0003
Mains equipment consists of a mains R. Ohms 6 v2 grid blocking ., .0002
transformer, a full wave reciif ing valve, 7-- 7 V2 somendecourflnun - .1
dimers and 1 1 5mg. 8 v2 A.v.c, decoupling .. .1
, h -k , 2 V1 17 .. .. .. 200 9 V2 bias decoupling .1
smoothing c oke (sped er field eneigismg 3 v2 screen decoupliiig.. 15,000 10 05c. grid ,. .0002
g XZVAéVdCefeepcln 25 mg i; 33 gecogpling .1. .000.
. _ - . o . ,. eou it: 5mg. ias econ 'n .1
f cums Rangoval. T1. abf? hf h 6 v2 bias .. .. . 200 13 H.F. by-pass 1).]. g .0001
alse bottom t at permis inspection 0 t o ; gscmogige, .. .. ._ 4g 14 L.F.oouplini: .. 1.2
so. mo 1 er ,. 15 15 v5 compensator .006
Remove the back of the cabinet (sliding 13 353833115 ~- 53.333 it Wemtml 32
clips) and the three control knobs from the 11 vi; 1315 L _, :1 :2 200 is iis'rbgringdfiiiiiiimg 0
These are of the grub screw fixing 12 A V c diodeioad (part) 3 meg 19 vi A.V.C.decoliyillnu
type. of the combined tuning and volume 5 i cemffikglygg if?! ssmoetil) it; fiflvggfggupégif
» ~ . - » y . . . e
Lontiol, the smallei knob is of tlie ginb 15 H.F.stopper .. 70,000 22 H.T. smoothing
screw fixing type and removal of thu 10 Eon; cauldroi Smog 23 P.U.shunt .
17 i0 e ioa . 3 men 24 5w. 2 pad . -
- . . . 18 Volume control 5 meg 25 S.W.l ad . . . . .005
tthlm Lilli: cabinet on itsb slide aiad ieilriove 19 v5 stabilise! 150 26 s.W. 2plixed mum" .002
6 our 0 95'51118 0 5 afi wafi'el? go 35 bin: 1% 27 MW. fixed trimmer . . .00025
e c assis 1 eiay ins 1 25 L.W. fixed trimmer .0000r
is them free to the extent of the speaker 3'2 A»V~C~fd ~ 31! 2 Omancdflew 9091
23 350. anbode feed . . . 3,000 80 FLF. toy-pass . . i006
_ 2 2sta iiiser .. ,. .. 50 31 H,F.b ~ a .. . 1
The speaker (secured by six bolts) can yp SS 000
éRli

Reception on {our wavebands
H.F. pentodo is employed as a pro-H.171 amplifier.

is provided by the Decca 99 All. superhet.

From the circuit it will he noticed that an
A double diode is employed {or seeonii detection and A.V.C.

Page 2

October 23, 1937

external speaker to be connected. This
should he of the permanent magnet type
with a matching transformer having an
impedance of 9,000 ohms.

When the receiver is ibeing used for
gramophone reproduction, V5, the LF.
amplifying valve, is used as an L.F.
amplifier. The pick-up input is injected
into the grid circuit and by means of
switching arrangements the output of V5
is lied to the grid of the pentode output
V1! V2.

, Circuit
Alignment Notes

LP. Cll'cuits.-Connect an output
meter across the primary of the speaker
transformer, and a service oscillator bee
ween the top grid and cap of V2 and

ssis. Switch the receiver to the
edium wavehand and short circuit the
oscillator section of the gang condenser.

QUICK TESTS

Qulck lens are available on this receiver on
the Ieadsto the speaker panel. Voltages measured
between these and the chassis should be :-

Red lead, 194 volts, smoothed er,

Black lead, 172 volts, smoothed 1LT.

Blue lead. 319 volts. unsmoothed 1121,

VALVE READINGS

No signal. Volume maximum. Mrw. band.
200 Volts AX}. mains. 1,000 ohms! volt meter.

. ectmde. Volts.

Jruztard.
1 \PaBfimetL. Anode .. m 7.7
Screen .. 194 3
Mallard
7 TH4A(7 met) Anode .. m 2.3
Screen .. 90 5.9
0sc.an0de so 3.3
Jlullard
3 vaii met) Anode .. 142 5.3
Screen .. 194 3,1
Mallard
4 zooms met) Dlodes - -
, only.
Mazda .
5 ACa/PENU) Anode .. 170 34

Screen . . 11M 7 ,9

mum
o 1W4/350 (a) . .

Filament 319 ~-

Vintage Service Data CD-Fiom

Wireless Retailer and Broadcaster (Supplement)

Turn the volume control to the maximum
position.

Tune the service oscillator to 456 km.
and. adjust T3 and T4 and then T1 and T2
for maximum, reducing the input from the
oscillator as the circuits come into line to
render the A.V.C. inoperative. The LP.
trimmers are sealed by red paper strips,
which must be removed before alignment».

Signal circuits.-Remove the short cir-
cuit from the oscillator section of the gang,
Leave the output meter connected as
before, but feed the oscillator to the aerial
and. earth terminals, via either a dummy
aerial or fixed condenser. Only feed suffi-
cient input from the oscillator to obtain
definite peaks in the output meter so as
to keep the A.V.C. inoperative.

Medium Waves-Time the set and oscilr
lator to 200 metres (1,500 kcs.) and adjust
first T5 and then T6 and T7 for maximum.

Tune the set and oscillator to 560 metres
(545 kcs.) and adjust P1 for maximum,
simultaneously rocking the gang to ensure
optimum results. _ .

Repeat both the above operations until
no further improvement is noticed. .

Loquaves.--Tune the set and oscrllotor
to 1,000 metres (1500 kcs,) and adjust first
T8 and then T9 and T10 for maximum,

Tune the set and oscillator to 2,000
metres (150 kcs.) and adjust P2 for maxi-
mum, simultaneously rocking the gang to
ensure optimum results, ' 4

Repeat lboth the above operations until
no further improvement is noticed.

Short waves-Tune set and oscillator to
55 metres 18,571 kcs.) and adjust first T11
and then "112 and T13, and then finally
retrim T11 for maximum response.

The padding is fixed, "but check at
40 and 80 metres.

Tune the set and oscrllator to 13 metres
(25,077 kcs.) and adjust first T14 and
then T15 and T16, finally retrlm T14 for
maximum response. .

The padding is fixed, but check calibra-
tion at various wavelengths Within the
range covered.

Two condensers rir me as are made by
A. H. Hunt, Ltd. For replacements, the
unit containing C18 and 022, list 3,475, is
at 85. 6d. C17 unit 5,351 is ls. 10d.

MAINS VOLlAGt.

L3 ADJUSTMENT 09 mi

_-_-_--

Decea 99 on
Test

ODEL BEL-Standard model for
operation on A.C., 195-225
volts, 5060 cycles. Price, 15,} gns.
DESCRIPTION. - Four-wave, six-
valve, including rectifier, table
model superhet.
Fmrunes.-Full-vision scale illu-
minated in sections by wave
switch. Concentric tuning and
volume controls. Combined tone
and master switch. Elliptical cone
high-fidelity speaker. Pick-up and
speaker sockets. Fuse in voltage
adjuster.
Lemma-75 watts.

Selectivity and Sensitivity

SHORT WAVES (12.535 and 55-90
metres).-Very good gain and easy
handling. No drift. Adequate
selectivity.

MEDIUM WAVES (200-550 metres?
-Very good selectivity with wel~
maintained gain. Local stations
spread on adjacent channels only.

LONG WAVES (8002.000 metres).
~Good gain and selectivitly. All
main stations received. S ight in-
terference on Deutschlnndsender.
Good background.

Acoustic Output

Ample volume for ordinary room
with very good balance and pleas-
ing tone. Crisp attack with flat
response and no noticeable
colouration on speech.

MAINS
ANSFORM

20

E
El T13 T16
no T17

B E
13 16 T12 T15 o
f IO

to V2
E Egi C16 5
18 T5 IEH' t {i335 K Cf]

F

W/C' TUNING

UWOLUME

TONE
0N/0FF

ONE

N/OFF

l0NlN6 C
UVOLUME W/

Pl l NEAREST TOPofCHASSlSl
P2 (NEAREST BOllOlll

l.

The simple layout of the upper side 01 the chassis ol the Decca 99 Is shown by the drawing on the loll. The layout

of the components underneath Is shown on the right.

or the cabinet.

www. Vin tage-radio. com

If necessary, these can be reached by taking out the 13159 bottom