Philips 577 a service manual

Page 1

July, 1936

Broadcaster Service Mans Manual 19

SERVICE ENGINEER

PHILIPS 577A SUPER-INDUCTANCE
RECEIVER

IRCUIT.-Signals arc fed to the first
H.F. valve, V1, an H.F. pentode,
via a bandpass filter which uses ta ped
inductancennd direct capacitative coupling
An inductively coupled H.F. coil feeds the
grid of the second ILF. pentode, V2, which
is coupled to the detector, V5, by a tuned
H.F. coil.

V5 is coupled through a resistance
capacity network to a pentode L.F. ampli-
fier, V4, which is linked to the pentode
output valve, V5, b a further resistance
capacity network. 5 is tone controlled
by C55, R28, and a variable resistance R23.

A.V.C. is applied to the grid of V]
through a decoupling circuit consisting of
R16, CB and R15, variations of potentials
being obtained across R17.

Mains is uipment consists of: Trans»
former, in l»wnve 1821 directly heated
rectifier, electrolytic condensers, and a
choke iii the negative H.T. line.

Special Notes.-Tlie external speaker
is connected on the high-resistance side of
the transformer, and should be of high
im edance.
ilot lamps can be removed by undoing
the, knurled knob and lifting out paxolin
strip.
The pilot lamps are 6 volt .5 amp. types.

Quick Tesla-In this receiver there
are no suitable easily accessible points at
which Quick Test readings may be
taken. It is advisable, therefore, to pro-
ceed at once with valve tests.

Removing Chassis. - Remove the
knobs (grub screws). Note that the centre
switching knob has two grub screws.
Undo tour fixing bolts which will be found
on the underside of the cabinet.

The chassis will then slip out far enough
for the usual inspection without unsolderr
iug leads to speaker.

Care should be taken, when replacing
chassis, to see that the rubber mounting
washers are correctly in place.

VALVE READINGS

No signal. Tone and Volume controls turned
fully clockwise.

v. Typo. Electrode. Volts, Mn.
lAll Mullanl
except icolilier)

1 vriainet.(5) Anode .. 250 .75

.5

2 vriAmet.(5) .73

.55

3 2DiAmet.(5) -

4 SP4mot.(5} .2

. .1

5 reii.4VA(7)., Anode .. 225 35,5

Aux.grid 2.50 3.75

a 12x21 (4) . Filament 250 -
(Philips)

A straight " circuitutilising high-
ei'fleieney tuned circuits is employed
in the Philips Model 577A Super-
inductance receiver. It incorporates

live valves and a rectifier.

ALIGNMENT

Preliminary ProcedureraSwitoh to
medium-wave band, connect output meter

across speaker and modulated oscillator
across aerial and earth.

Medium-wave Band.-Set modulated
oscillator to 225 m. and tune in the signal.
If the pointer is incorrect it can be ad-
justed by means of the drivin plate,
which is the plate holding t e scale
assembly to the chassis. This is adjustr
able by loosening {our screws.

Tune for maximum response on the out-
plii. meter by means of 059, (115, 016 and
C 7

Set modulated oscillator to 500 m. and
check the pointer again. Re-check the
pointer at 225 in. and 550 in. Adjust
drivin plate to get the correct scale read-
ing. Repeat 225 m. and 350 m. and check
again at 500 in.

Check all the above settings, and then
tighten the four screws.

Long-wave Band.~Change over to
long-wave band and adjust both receiver
and oscillator to 1,000 m. Trim, by means
of 018, 019, C20 and 021, for maximum
response on the output meter.

Reseal trimming condensers with sealing
wax.

(For circuit and layouts, see nexl
page.)

Taking Valve

IF the anode current at the correct grid

voltage appears correct and a valve
still fails to give the presumed ' plifica~
tion, the slope luid amplification factor can
be roughly checked in the following
manner.

The slope is the relationship of the
change in anode current with respect to
grid voltage. For example, a slope of
5 m.a.,'v. means a change of 3 ma for
change of 1 grid volt. Most niaiiulao
turers rate their valves at zero grid bias.
and 100 volts on the anode,

A valve test circuit should be arranged,
and the change in anode current noted
while the grid bias is increased to, say,
minus 1.5.7 By simple proportion the
change in anode current for 1 volt can be
calculated. ,

Measurements should not be taken at
zero grid volts on power valves. since the
total filament emission may be greater
than the maximum for WlIlCh the valve
is rated. The measurements should he
made at a higher anode voltage with the
requisite grid bias as shown by the makers
chart.

Characteristics

The amplification factor is the ratio of
the voltage produced in the anode circuit
to the applied grid voltage. The anode
current. at a given high-tension voltage is
noted at a given grid bias value. The grid
bias is then increased by a few volts, for
example, 5 volts, when, of course, the
anode current falls. Extra voltage is then
added to the high-tension circuit until the
former value of anode current is again
reached. The extra voltage which has
been added is noted and this is divided by
the change, in grid Voltage which was
applied to the valve. ll 15 volts were
added, then the amplification factor of
the valve would he 5.

From these two values we can calculate
the impedance of a valve. 11, is only
necessary to divide the amplification factor
by the slope and multiply the result by
1,000. For example, a. valve with an
amplification factor of 14 and a slope of
2 would have an impedance of 7,000 ohms.

(The above notes are extracted from the
section on valves contained in the 1956
BROADcAsTnn Radio and Gramophone
Trade Annual ").

Page 2

' 7
20 Broadcaster Service Man 5 Manual July, 1936
l PHILIPS MODEL 5 A C ' d
i 77 ontmue )
c, Candenaen(0mmnud)l
RESISTANCES CONDENSERS i -.--
0 Fur itse Mfd 29 V4 gm bypass l.
a Pin- 59 Ohms LJ-P-J-' 3" V "Me by? ~~
~ 9° ' - 1 HT smmmn 32 31 v5 L1, coupling ..
. - - l 3 ~ .. 32 V5 grid by-nnsa
1 Constant gain control .. 030 2 in: smoothing .. .. 32 33 Pm to t 01 or
2 v1 and v2 bias ptr. .. 100 3 v1 screen lay-pass ., .. .1 s4 1, we 9cm ' .115 '
3 Vi unii v2 bias ptr. .. 32,000 4 v2 anode by-pass .l .l .l 85 53300 9 $9M 3
4 v4 screen decoupling .. 04.000 5 v1 anode by-pass .l .1 .16 HF if; ~ --
5 v1 screen decoupling .. 1,000 6 v4 screen by-pass .1 37 143 -_w 8 mad. --
0 v2 anode decoupling .. 1,000 7 cathode by-pass. 105 38 1 EMS: Egg
7 Vi screen decoupling l. 1 meg. s _ enthoile bit-pass. . .05 39 1331 $151.33 S --
. a v4 anode decoupling nu. ,. .l meg. ii A.V.C. deennpling ,. .1 40 v4 can. de b If ~
9 Vi cathode bins .. .. 500 10 V5 bins by-pass .. .. 25 41 Anode dz) films
10 v2 cathode bins .. .. 500 11 Aerial Luning.. .. ., 00043 42 mm 33.81!) 3 ..
11 A.V,Cl decoupling .l .. 32,000 12 1st H.l-. tuning .. .. 00043 1 -- --
12 A.v.c, decoupling .. ., 32,000 13 2nd HF. tuning .. .. .00043
i3 Vi. grig 100E .. l. % meg. 14 3rd g'F' tuning ,. .. .Ogggs
4 v2 gri lea ,. .. .. (i meg 15 lat .F. trimming .. 0 27 .
15 v3 anode dacoupling .. .32 mg. 16 2nd H.F. trimming .. 000027 Malda Valve Connection
10 v1 A.v,c. decoupling 1 meg. 17 3rd in. trimming .. .. 000027 Chart
1 i7 Villain: léoutml .. .l .5 magi 18 Pm; wave 233 .. .030327
. a v4 gri ecoup ng .. 1 meg. 10 mg wave 1') ing.. 0 0 27 . .
1 19 v4 cathode blas .. .. 4,000 20 Long wave padding .. 000027 , A Wall Chart, glvmg the base Connec-
20 v4 anodebdeooupling ptr. .. .22 mg. 21 L030 wave puflidingl. . .000027 Mans of Mazda Valves, has been made
21 v5 grill in l. ., .. . meg. 22 A. .c. dewupng .. ll 00003 N 11 . . .- .
22 V5 le. wupling ., .. .l meg, 23 Bund»pass filter coupling .. .025 $125331: {agita1frs gagglferiécie 933."3
23 Tone enntml .. ll 50,000 24 Band-puss filter coupling ., .032 ' e u E D- Y n S 9513'?
24 Coil Bhauil , izfizomeg 25 v1 grid. gawupiing l. 000025 for atrarglance referelwe.
25 v0 gri in H .00 20 v2 grid ewuping .. 000025 . ' ' n char 5 be
20 v5 gxid nine .. , ,. 04,000 27 v3 anode decoupling . 000007 afipplggaifi-s it; amen m: Choulitd
27 v5 griii decoupling ,. ,. 1,000 25 LE. coupling .. .. .01 m e 59 W 11 6° 0-; -l
28 Pm tone control circuit 1. 100 (cmmumm Malcolm"). at 155, chairing Cmss Road, London,
W.C.2, or to branches of the company.
A kll
3 0 C9

MAKNS

TRANSI.z

223 %
C24 C22

__.__.__--..__-_.__.____- _._____ __.__..I

Two H.F. valves, a detector, an L.F. amplifier and an output pentode term the basis of the 577A circuit
Although siraigh the circuit incorporates A.V.C.