Philips 720 a service manual 2

Page 1

ELEBTRIGIL ANII RAIIII'I 11111111115 SERVICE CHM

PHILIPS 730A,

Tuned anode coupling is used to transfer the
signal from VI to a second HF amplifier V2.
L5 is the MW coil and L6 the LW cml, both tuned
by VC3, which is ganged to VCl and VC2. C9
is the blocking condenser with R9 the grid [0
cathode resistance of V2.

blocking condenser operating also as a grid con-
denser, With R12 the gridleak for rectification. A
high resistance pickup may be connected to the
sockets provided and when this is done bias is
applied to the grid of V3 from the voltage drop

across R23 in the HT

negative line De-
coupling is eifected by
R22 and C28.

LF signals from V3

. . are resistance ca acit
The s1gnal 15 transferred from V2 to the triode RESIST'ANCES coupled by R151) and
720A detector \(3 b}: aperiodic tuned anode choke L7 R 0" R mm C20 and R17 to the
across which blS 15 shunted on LW. C14 is a " rid of the LF am ii-
1 l6000 8 . P.
2 [0:000 fier V4. This valve 15
WINDINGS 3 32,000 biased from R123 and
Five-valve ,plus rectifier, Iwa-waveband TRF L 0h L Ohms 4 mg a tone contra com-
racgiver Madagamringkthree 5Fh5ral11gex. de- l_-~ 3W7 v9._-l g m % 5'15; Ci? lggtesdmgii
vumn ulna e ara pic -up an a ig impe rmce -- .1 19 32: .
extra Iaudspeaker in the 730A. The 720A is in g 5 fil'i 1 " 1 3%}, ii 125% 20 311% the chasms deck at the
a moulded cabinet and has no internal Inud- 4 lg iZ-ilfiiizotal) " 3B 9 lmeg 2| 16.000 '92"- Hl filtering 15
speaker or matching transformer. Suitable for 5 3 13 H :: _[ ll) 12 500.000 [5ch by C, R16
opefarian A471»: 116 "141531.; £00 220v 40-100 6 15 14 (tutal) 560 05 i; .1 .. 210,000 23 100% and C18.
eyc es ar ere m l y P up: Lampr 7 37. 15 .. . A second stage of ,
Ltd. Service Dept., Cherry Orchard Road 8 ~ -~ 1 51.3232: iggggnf: Wfiyhflmsc ;f°w&'ow$esi§a§63 $510? capacity :izctmznyhiiflidrytwa
Cmydan, Surrey. - Model 730A Only ohms : 80.000 for 100,000 ohms ; 1.25 meg for l meg ; couphng 1ncorporatmg Mme Superinduct-
Two aerial sockets are provided A1 for V6 y iNormal low impedance in later models. etc. R19, C22 and LRZO Ince."
strong transmissions and A2 for normal
rgceptioat. The ftcapagity denoted by Cldis actually
i e .
sockitot: enser e ect etween the Al an A aerial VINE, V5'V4. V5. V6. BLOCK A BLOCK B. BLOCK C
From A2 the signals are fed via_ an aerial trimmer G G Al C24 C29C [5 Ci I C5 C6
T7 to a tappinfi on the MW primary winding Ll
of a band- -pass lter unit comprising L1, L3 (MW) 0 O O
and L2,edL4b(L 3%] Th; txgzsecgottis (if the filter H 000 H H' O 00 H H O O H H O O H 27C26
are tun y an w 1c are ganged,
1mg bandpass coupling is effected by C2 and C3h 0C C 05 T T T T C
ront a tapping on L3 s1gnas are e to t e
grid othl,b_whioh hials a géiin 1control R7 giigh O O 0 :TL 7:?- T
varies t e 1:15 on t e gri ermanent seat 0 e
biasing is effected by R2 decoupled byC A A A2 C 2' C '2 I
$4VB 244v PM24A 1821 C28 )7, Clb 00 MT, c4
R3 R5 ERQ L8 L9 LIO J. 7
C2 CONDENSERS
C Mfd
Cl R4 Reg 1 . very 10W
- 2 .05
AZ II-OAI 2
FUSE
L1 T7 1.3 V6 2
J: 7*
15,. C g.
ID
11
.. . V; M 1 5 1%
L U2 14
i 15
T6 L14 ]6
I7
1_ 4 C is
L2 .1. WW! 1 PILOT £3
1' ~ __> . _ LAMP 21
.LCZ T C 241529 g
T _ L|5 5| at
E: C3 R23 R24 if 33
_ R22 L11
. MAINS g;

11.. ma and 120A roeeivnrn were two or the law commercial at. made with two hithequency mm.
To avnid lour ganged stages, coupling between V: and v: 1- Iperiudie.

with blndpus

NOVEMBER 1945

preleleetion.

Th. circuit is tun-d radio-frequency

Maybe 0006411113.
1' May be 002 mfd or 0075

1 May be .064 mfd.
Ii!

Page 2

PHILIPS 730A
re-Contd.-~-

These two drawing: iden-
(My all part. on the 130A
u-e oi solid hiuk

mm speeds railr-
once by distinguishing from

condensers. Details of :0...
denier blocks A, a and c
are on page iii.

passes on the LF signals
to the grid of the output
penlode V5. This valve is
biased by taking R20 via
decoupling components
324 and C29 to a tap-
ping on the smoothing
choke Lll in the HT _ .
negative line, so that V5 bias is derived from
ihe voltage drop across R23 and a part of
II,

A permanent degree of tone correction is
efiected by C25 and in the model 720A two sockets
are provided in the anode Circuit of V5 for the
connection of a high impedance speaker. 1n
the model 730A an internal speaker is provided. in
which L8; L9 is the output transformer and L10
the speech coil. Sockets for an extra loudspeaker
of the high impedance type are provided across

8

The power supply is derived from the usual full-
wave rectifier V6 with smoothing ell'ected by a choke
lélzl7 in the negative lead and condensers C26 and

GANGING .

MW bandilnject a 225m. signal into the aerial
and earth sockets, using AI socket unless the signal
is very weak. Switch receiver to MW by pulling
out the tuning knob and time it to 225m. on the
scale Adjust T1, T2 and T3 for maximum output.

LW band-Switch receiver to I_W and tune to
900m. on the scale. Inject a signal of this wave-
length as before and adjust T4, T5 and T6 for
maximum output.

Aerial matching-With the receiver connected
to the aerial with which it is to operate, tune in a
broadcast transmission at the lower end of the
MW band and adjust T7 for maximum output.

VALVE READINGS

V Type Electrode Vail: Mn.
.- s4vn (met) Anode 175 3
Mullard Screen 95 .5
2 S4VB (me!) Anode US 3.5
Mullard Screen 95 .5
3 WV (met) Anode 60 3
Mulliud - fl -
4 244V (met) Anode 100 2.5
Mullard V ~ 7
5 PM24A Anodp 195 17
Mullard Screen 170 3
6 1821(Philips) Heater to we -
chassis

Pilot lamp : Philips type 8046. 6 volt. 3 watt S.B.C.
with centre contact.

W

8R5

6
MAINS
TRANSF g

G

FUSE

SPEAKER
LEADS

@t

,
Instability in Dye Receivers
SOME of the Pye receivers type MP I44 become

unstable after a time and the trouble appears
to be due to slight changes occurring in the IF
circuits. It is generally easily cured by alteration
of the coupling between the IF coils. _
The IF trimmers are fixed so far as capacity is
concerned and the movement of the coils changes
both the coupling and tuning slightly. It will
efiect a cure for the oscillation and when properly
adjusted will not lower the sensitivity or afiect the
tone-F D.L,

Os ation in Output Stage

AN Alba AC model 90 receiver was brought in
for repair with the output valve, a Mullard
PEN4DD, showing a bad cathode-heater leakage
when hot. On changing the valve for a new one of
the same type, and fitting a new bias electrolytic,
the set became unstable and would not time in any
transmission on an waveband ; the only sound
was a loud hissing rom the speaker. _ .

Two more valves of similar type were tried With
the same results, although all stages appEared to be
operating correctly. Finally the removal of the
C17 (Survice Engineer Sheet) .005 mfd. pentode
compensator condenser connected between the
anode and cathode of the PEN4DD completely
cured the fault-S. CARTER.

Reasonable quantifies for sale
to the public . .

available from your
factor

Now i

Size 2. Multicore Solder
Cartons. Each contains suffi-
cient quantity of Ersin Multi-
core Three Core Solder
Wire to make 240 average
solder joints. Cartons are
Very attractively printed in
three colours. Net trade
price 4,- doz.

Like the makers of many other good things we have for
months been trying to keep up with the demand for the 6d.
Multicore Cartons. More supplies are now available to
meet the demand which has been created by consistent
advertising in hobbies papers such as Practical Mecha-
nics, Practical Engineering," English Mechanics,
Practical Wireless and selected national newspapers
having a combined circulation of 8,000,000 readers. Get
your share of this profit making business by ordering a few
dozen cartons NOW I

Service Department.
Order nominal l-lb. reels
of Brsin Multicore Solder.

We
is. soiuiu {}

MULTICORE
SOLDERS LIMITED

Net trade prices :
Commonwealth House, New Oxford Street. 13 S.W.G. _ . 3/3
London, W.C.1. Tel.: CHAxicery 5171.2 15 S.W.G. _ _ 3/?

NOVEMBER 1945

for use in your ownI