Philips 838 u service manual

Page 1

ii THE WIRELESS AND GRAMOPHONE TRADER

TRADER SERVICE SHEETS

NUMBER EIGHTY- SEVEN

PHILWW

838U

3-VALVE (Plus Reclilier) A.C./D.C. RECEIVER

lhilips embody a 3-valvc (plus rectifier)

chassis using a variahhrmu pcutode
H F. amplifier, 3 pentode detector and .1
pentode output valve.

CIRCUIT DESCRIPTION

Aerial input via series condenser ()1
and Droitwich \vuveetmp L1, 022 (~ihort»
circuited on M \V. and normal I_\\.
position by switch 8!.) to coupling coils~
L2. L3. Single tuned circuit L4, L5,
024 precedes Variable~iiiu peutode H F.
.iniplificr (V1, Mullud metallised VPIBAJ
operating with gam control by variable
cathode r ' tance R5.

Tunudr , ondnry transformer coupling
by L6. L7, L8, L9 and 028 to H F
pentode detector (V2, Mullm'd metallised
SP13) operating on grid leak system with
Clo and RB, R10. Voltage developed
across R10 section of grid leak is fed
buck through decoupling circuit R7,
C7 as (LB. to HF, amplifier, giving 2i
_ nple form oi automatic volume control
H1". try-passing in V2 anode circmt by
condenser 014. No provision for gramo
phone pick-up.

Resistance-capacity coupling by R13.
013 and R14 to output pentoue (V3,
Mullnrd Pen28). R15, 017 and RIB form
H filter in control grid circuit; 018
in anode circuit is tone corrector Pro
ViSion [or connection of high-impedance
external speaker across special secondary
on internal speaker transformer T1.

\\'hen the receiver is used with AC.
mains HT current is supplied by a
halfrwme rectifying valve (V4, Philips
0Y1), hich, with l).C. supplies, behaves
as a resistance of low value Smoothing
by LF, choke L11 and large-capacity
electrolytic condensers 019, Cm.

Val re - heaters are
connected in series,
together With scale
lamp and automatic A
voltage regulating barv Cl
i'etterlanipmhflips Cl)
across mains input
0 ,cuit.

DISMANTLING

THE SET

IN their 8381] A.C/DC. receiver

ol normal repairs being carried nut
To free the chassis entirely. remove the
speaker input transformer from the
siib~bafilc (two round-head wood screws).
disconnect the leads coming from the
chassis, and replace the transformer

Before it is possible to inspect the
under-cliassm Components it is necessary
to remove the screen (two screws).

When plating the chassis, take care
that the stud on the pointer drive belt
enters the slot on the clip (in the pointer
carriage, and connect the speaker leads
as follow, numbering the contacts Irom
front of cabinet to hack :-Top contacts :
i, yellow»black ; z, yellowrgreen Bottom
contacts: 1, yellowrred; 2, yellow: 3,
bare tinned copper.

Removing Speaker.~To remove the
speaker, unsolder the leads from the
secondary oi the transformer and slacken
off the four clamps holding the speaker
to the subrbafilc.

COMPONENTS AND VALUES

Kesista h
it! i Aerlal-imrlli sliunl V
; [<2 l V! grid Murm- . .
R3 )larts ni \x . ., potential
R4 dividlr . .
R; l \i gain mnimi
Rn , Vi nrod on. rmsinucc
, R7 : A.V.C. llnl decoupling
RE \'i anode decoupling . ,
Ra '~
km \.gnd|enk ,. {
im v: so HJ. red ,. ..
1m vi Alimlr ind so docunpiing 20,000
Rx; \'z anode linil .. 320,000
km \3 grid menu» ninooa
5:2 l}v3 grid H.F. stoppels { 2:332
in; . v; auxgrlti H.T.Iecd .. 20,000
ltiE ( V 5.3. rcsistancc . . 320

Riu H T inDnlv
Two 640 O resistances in parallel.

iiasi A

March 7, 1936

leiies
Condensxh (/lll
Ci , Aerial seri oudcnser ,. 0-00]
L; Eanii blocking condenser , . 0']
(3 Aerial I_.W. Coupling trimmer n-nnnoil
C, Vi gm! Cmidmulr (yo/mum
(,5 vi s G. byrpass . (M
M V: ga toiitril] 5V1); 0;:
(7 A. . lne lieu! c 0']
l 01 vi c, thndc, byrpass r) i
(0 Vi anode {mourning n i
V2 grid candcnsvr (i now igi
V2 5.6, byrpass . . o i
V2 anode and 5,1; decoupling 0 s
L F. coupling to \ 3 . no:
, anode H.F by s . n nnnir;
V3 nux giid by-Pdss , 0-;
Toni: Corrector . 0-004
\3 End ii 1. bypass "110nm;
Y3 cathode 15 .,
}H.T. smoothing { :1:
\4 anoderalhodc bypass . n l
Dmiiwii wave trap tiuiiiig .. o mum
Aerial t Ln: tnmmci . . 0 000027
Aerial circuit tuning . n mois
Aerial Cucllit main trimmer . 0-000027

H.F. transformer M.\V. trimmer (i 0000:?
H . transfjrmerl trimmer o-unonz7

Izlerrrolync. ttviriahlr. il'rr-seli

Values
(otmsl
w 5
L3 Aerial coupling coils . . 1:: 3
1E: Acn'al tuning coil: 3
f; H. ,transformerprimaiy ((23
f; n. . traiisformcrsrcondary { 1;;
Ln; Sprakerspeeclicoil ., , 5n
Lir HT, smiothing ihnke . . 7ou~o
Pri. ,. 250~o
Tr Speakcrinputtrans. Sec,(int.l' on
_Su\(ext.H Lion-0

si s, Wavcband switches .. .
$5,5o Minis Switches [ganged \Vltl]
l Rs) .. .

VALVE ANALYSIS

Voltages and currents given in the table
on the opposite page were measured with
the receiver operating on AC. mains of
220 V. The volume control was at
maximum and there was no signal input.
Voltages were measured on the 1,200 V'
scale of an Avometer, with chasSis as
negative.

Removing Chassis i I
To remove the chassis :1
from the cabinet,
remove the three
control knobs (re-
cessed grub screws)
and the four bolts
(with washers) holding
the chassis to the
cabinet bottom. Next r

no.
,_.

cs
R2 :

free the scale lamp
and its holder from
its support, when the chassis can be
withdravvn to the extent of the speaker
leads. Free the speaker leads from the
cleat on the side of the chassis, giving
suflicient slack on the leads to allow

(:2

L

Circuit diagram of the Philips
838U A.C,D.C. receiver.

V1 Vl V!

Page 2

March 7, 1936

Anom- mm
mm \ull: mum-m
mm;
V. . __ if 7
Vi \'lr1A mu

\zsl

GENERAL NOTES

Switches-Sb are in tun lulu)"
units oi the usual lllillps desmn, 51.5'3
being on the unit nearest the Umtrnl
knob, with S4 on the othitr unit [n
the front unit, looking tit thi Lndorsn L
of the chum i 81 is at the trip, 82 is it
the bottom and S3 is lit the right linml
Sldt. 'l'ht- switch pomtiuns tor the \d.I'|I)\i.\
control settings are given in lie Lillll
below" 0 indicating open. and C rloseil

rimmu.
lmm:

54

if,
S
mains switches, ganged Wltll R5.
Coils. L1, the Droitwich \\fl\'l"II.ll

rail, is beneath the chassis. L2-L5 mil
Lfl-Lfl are in two units on the cli.issis.
Scale Lamp.il'his IS a Philips. ..t \
0.: A centre Contact S B C lamp.
External Speaker.~lhis shxnild lc
Lonnocted to tho sliicldrtl ockols providr ll
at the rear of the has The Fnht' p n
may be neglected, The speaker whould lit
at the high impedance ty
Speaker Transloriner.~Notc aliut this
has tiio secondaries, one of lo .17
pedance ior the internal speaku' spemh
c011, and another of high impedaice for an
external speaker In all there are sum ri
i-onncctions to soldering studs on the
unit, two for the primary, two each for
the two secondaries, and one for whiil is
apparently an electrostatic SCYLJIL This
is connected to chassis. \ilieitas one Sula

THE WIRELESS AND GRAMOPHONE

III

SPEAKER LEAD

W » MAINS -
: g CONNECTOR

Plan view ofthe chassis. R16 is a flexible resistance inside the lead to the top cap of V3,

')l the external speaker secondary and tht,
core DI the transformer (and speaker
chassis) are connected to trim earth.
Trimmers 023, 025, 026, C27.- These
([11) 0f the usutil Philips tubular type
Condenser 010. *Thl: is also of the
tubular type, but is not to be adjusted

CIRCUIT ALIGNMENT
According to the makers' instluctions,
it Will be necessary to obtain from them
an artificial aerial unit (ZOUMMF) and
an auXiliaty dial which is lured to the
thzissis. The set must be run from A C.

mains, through a double-wound mains
transformer, and the chassis can then be
enrtlierl. Connect up an output meter
to the external 14.8. sockuts,

Open the trimmers 025 and 026 its
far as possible, and switch the set to ALW.
Adjust the negative bins of V1 to 7- 3V
with the aid of the volume control
measuring between chassis and cathode
of V1 with a low consumption D.C.
voltmeter. Turn the tuning condensers
to zero, apply a signal of 180 m. from an
osmllator, and adjust C25 and 026 for
maximum nutpnt.

Now apply a signal
of 225 mi, tune on the
set for maximum, and
il necessary loosen the
screws ()1 the driving
dial and adjust the
latter until the auxili-
alydialindicates225m
Now rc-trim 025 and
026 at 225 m.

Switch receiver to
l..\\'., apply a 900 in.
signal and tune to
nooni. X0 adjust
023 and 027 lm maxi-
mum output

To adjust the Droit»
with filter, swttch to

l,.\\'. itliird position (if
snitch bringing filter
into ciituit). tuiic to
Druitwich Ora 1,500 in.
Slgllzll, and adiust (:22
lot minimum output.

Under - chassis View.

C22 is adjusted through

a hole in the side of the
chassis.

C3