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.