The Gramophone Company 440, 444 Service Manual

PRIVATE A N D C O N F I D ENTI A L

“His Master’s Voice

SERVICE MANUAL

FOR T R ADE USE

> *

for

FOUR VA LVE

BR OADCAS T BAND A.C. RECEIVERS

Mantel Models 4 40 and 4 44

TECHNI CAL SPE CIF I CA TIO N

V O LTAG E R ANG E

200 to 250 volts, 40 to 50 cycles.

It is i mp or tan t th at th e re c eive r be opera t e d
at th e cor r ect volta g e ; the vol ta ge tap s on th e
mains tr an sf or mer should be ut i l i z ed as f oll ows:

Voltage of Use Tap

A.C . Supply : De s ignate d:
200-23 0 volts 230
231-2 5 0 „ 250

C O N S U M P TI O N

56 watts .

W AVE-LENG TH R ANG E

187.5 to 550 metr es, or 1600 t o 545 kilocy cle s .

M AX. UNDI S TO R T E D P O W E R O U TP UT

3.0 wat ts .

D I M EN S IO NS

Height

15i n.

W EI G HT

Net

I 8 f lbs.

L OU DSPE AK ER

These mod els use a 6ln. cone spe a ke r .

DC resistance of fie ld, cold 1500 ohms.
DC resistance of voice coil .. 2.2
400 cycle impedance of voic e coil 2.4

VAL V ES

6A8G, 6G8G, E L 3( N )G , 5Y3G .

C I R CU I T D ESC R I PTI O N

The 6A8G p en ta g rid co nve r te r is co u p l e d to

the aerial by means of an iron-cored Li t z w i r e

tra nsf o r me r , which gives impr ov ed gain and

Widt h

11 in.

Dep t h

8in.

Gross

23 lbs.

se lect i v i t y . The c on verte r is f ollowe d by a single
stage high gain inte r mediate fre q ue nc y amplifi e r
uti li s i n g a 6G8G typ e ampli f i er tube.

The i nterme diate t ra nsfor mer s are also of

iro n-co r ed Litz wir e c on stru cti on.

The pri ma r y and se co n d ary of the fi rs t trans
for me r are specially designed t o giv e the o r de r o f
gain and sel e c t i v i ty re q uir e d.

The 6G8G tube, by means of its two diodes,
also pro v id e s AV C bias bo th for its elf and the
co nv ert er, as wel l as the d emo du l at ion of the
IF signal.

The audio out put o f th i s tube is resistance
capacity co upled to a h i gh -p owe r se ns it i vit y outpu t
pen to d e type EL3( N)G, whi ch d ir ectly feeds the

o ut put tra nsf ormer .

Pow e r is s u pp lie d to the main cir c uit s fr om a

di re ct l y heated rec t i f i er ( T y p e 5Y3 G), thr o u g h
the usual field coil fil t er em ploy in g 8 uf w e t
el ectro l yt i c condensers.

The osc il l a t o r plate and 6G 8 G screen grid
are fed t hro ug h a separate resistance capacity
fi lt er t o f urt her imp rove s t abil i t y.

Padding of th e osci l l a t or tun ed c i r cu i t is ob
tained by means of a va ria ble i n duc t a nce secondary

and fixed padder con d e n se r wh ich minimises
cal ibra ti o n dri f t due to va ri a b le p a dde r shunts.

A. V .C .

Ref er r in g to the cir cui t diagra m on page 4,

it may be seen th a t th e A VC dio de of the 6G8G

is delayed by an a m o u n t c orr es p on ding to its

cath o de voltage above g ro und . T his delay is

abo u t 4 volts negative wit h resp e ct to cathode.

Only one half the to t a l de v e l o p ed voltage is
uti li s e d for c on t r ol purposes in or der n ot t o
seri ou s l y li mit the po wer out pu t on w eak signals.

TO N E C O N T R O L

The ton e is co n t rol l ed by a series resi sto r-
cond en s e r com bin a ti o n across che out put trans
for mer pri mary; the vario u s values being selected
by a 4- p o s i ti o n sw itc h.

PRE LI MINAR Y TESTS

The foll owing tests shou ld be made:

(1) Un f i l t ered H T+- (ter mi na l 4 on speaker

sock et) t o chassis 339 volts.

If volta g e is low , check li n e volt a ge to see
th a t t ra ns f ormer is wo r ki ng fr om c or r ec t
pr i ma ry ta p, also try repla c in g 5Y3G .

Als o test f i l ter condensers for leakages.

Do tests 2 and 3.

(2) Filt e r e d HT (t e r m i n a l 3 on sp e ake r so c ke t ) to

chassis 248 volts.

If vo lt a g e is lo w , check output fi lt er con

denser. Do test 3.

(3) E L 3 ( N ) G plate cu r r e nt. Ch e c k volt a ge dro p

across output tr a ns f ormer primary (t e rm i n als

I and 3 on speaker so c k e t) . Thi s sh o u ld be

11.5 v o lt s . If high or low and vo lta g e s on

tests I and 2 are O. K., try replacing the
EL3( N ) G .

(4) Chec k all valves fo r fil amen t c on tinuit y and

free d om from i nt er - el ec t ro de shor t circuits.

(5) If fau lt st il l persists, co m par e voltages w i t h

table on page 3.

N ote. —The foregoin g tests can only be
carried out afte r removal o f chassis from cabinet.
The sp eak er so ck et nu mbe r i n g wil l be found by
con s ultin g th e diagram on page 4 and noti n g that
the nu m be rs given f or th e sp e a k e r plug are corr e ct

on ly wh e n v i e w i n g socket fro m inside the chassis.

IM PO R T A N T

Al l the above voltage tests sh o u ld be made
w i t h a voltmeter having not less t h a n 1000 ohms
per vol t of th e fu l l scale read in g, and should then

be wi thin +10% of the specifie d values.