Philips v 7 a service manual

Page 1

PHILIPS
V7A

Four-valve. plus rectifier, thres-
n'avebund super/11'! for operuliun
from AC mains, 110, 125, 145,
200, 220 and 245 volts. Provision
is made for the come: 'on of a
pick-up. Made by Philips Lumps,
Ltd, Service Deparlment, 74-94,
Cherry Orchard Road, C luydtlfl.

IN MW and LW the aerial input is
fed via C1 to the coupling coils,
L2 (MW) and L3 (LW), of the band-pass
filter, L4, L6 (MW), L5, L7 (LW). The
coils are tuned by VCl and VCZ sections
of the triple-gang condenser. inductive
coupling is provided for the lower end of
the MW range by LS and L9, while
capacity coupling is by means of C4 and
C5. An IF aerial filter is provided by
L] and C3.
On SW the bandpass filter is not

E A 2
r-*-

MARCH, 1 943

PILOT [AMP

employed, the aerial input being con-
nected to L10, which is a coupling coil for
the single tuned circuit comprising L11
and VCZ.

The control grid of the frequency
changer valve, V1, is fed via R17, the
grid stopper, and is returned via R2 to
the AVC line.

The first two grids of V1 are used in the
conventional manner as an oscillator
triode employing a tuned grid circuit.
R3 is the grid leak, and ts and c9 the
grid condensers. Ll2 (SW), L13 (MW),
L14 (LW) are the grid coils tuned by
VC3, while the reaction windings in the
anode circuit are L15, L16, and L17.

The oscillator anode voltage is derived
from the HT line through R15 and R16,
while on SW R4 is switched into circuit.
The screening grid of V1 is also fed from
R15.

The IF output from V1 is coupled by
the IF transformer, L18, L19, to the
grid of V2, the IF amplifying valve, and a
second IF transformer, L20, L21, hands
on the signal via C15 to the signal diode
of the double diode triode, V3.

The signal diode load comprises R5,
filter resistance, and R6,. the Volume
control. The slider of the volume

L18 L19

control is connected via C17 to the grid
of the triode portion of V3. The PU
sockets are connected across the volume
control without any switching. Bias is
obtained via a resistance filter network,
R7, C18, R8. to the negative end oleE.

The AVC diode of V3 is fed from L20
via C16, the diode load being R9. from
which the grid circuits of V1 and V2 are
fed via the filter resistance, R10, and
condenser, C12.

The LF signals are resistance-capacity
coupled by R11, C20, R12, to the grid of
V4, pentode output valve. through a grid
stopper, R13. V4 is cathode biased by
R14, which is not decoupled, thus pro-
viding a degree of negative feedback.

The output from V4 is transformer
coupled by L22, L23, to the permanent
magnet low-impedance loudspeaker.

The HT supply circuit comprises V5,
the full-wave rectifier, with its anodes
strapped," operating as a half-wave
rectifier. The output is smoothed by
R17, C24, and C25.

GANGING. ,

IF Circuits.-Inject a 128 kc signal via
a .032 mfd condenser to the control grid
of V2; adjust T1 and T2 for maximum
output.

L20 L2|

Inject a 128 kc signal Via a .032 mfd
condenser to the fourth (control) grid of
V1, and adjust T3 and T4 for maximum
output. _

The above trimmers are windings on
an insulated bush internally sprayed with
a layer of metal. The capacity is adjusted
by unwinding some of the wire until the
output meter, having reached its maximum
deflection, commences to drop back. A
turn or two of the wire is then replaced
and the surplus clipped ofl', the winding
being held in position by wax.

IF Aerial Filter.-This is adjusted by
varying the distance (and hence the total
inductance) between the two windings
comprising L1. The windings are held
in position by wax, which must be warmed
so as to loosen the coils, which can then
be slipped along the former. Adjust
them for minimum output.

Some models are fitted with trimming .

condensers in place of the variable coils.
MW Bani-Fully close T6 and adjust
TS to half capacity. Switch to MW and
set tuning condenser to minimum capacity.
Inject a 1,450 kc signal via a .0005 mfd
condenser to the aerial socket. Slowly
rotate the tuning condenser to the first

The circuit of the
V7A shows a four-
valve plus rectifier
three waveband set,
| basically conven-
tional, but employing
i characteristic Philips
[ features. For ex-
I ample, the HT to the

output valve is
I smoothed only by
1 C25, and the other
' smoothing is by re-
] sistance instead of

inductance.

RESISTANCES
R Ohms

i
l

=Eoou4auacm-

Back view of the V7A showing valve
and trimmer positions and L1, the
variable inductance IF filter.

signal from minimum capacity and tune
for maximum output. Adjust T5 and T6
for maximum output.
LW Band-Leave the tuning condenser
in exactly the position found when carry-
ing out MW adjustments and switch to
LW.

Inject a signal of 411 kc and adjust T7
for maximum output.

VALVE READINGS

V Type Electrode Vail: Ma
1 set Anode 230 1.9
0y; anode 7o 2
Screen 70 3.5
2 VPE4 Anode 155 6
Screen 155 2
3 TDD4 Anode 60 .5
4 PENA4 Anode 245 33
Screen 225 4.5
Grid 5 -
CONDENSERS
Mfdx 1 c M/Hr
.ooooz .
.oooos .
.oom .
.016 .131
.025 is .25
1.000002 19 .001
.01 1 20 .001
.0007 : 21 .002
.00149 22 .1
,000155 , 23 .1
.000165 24 32
.1 1 25 32
13 ,. .000155 1
WINDINGS
L mm: 1 L Ohms
1 1 12 25
2 1 7
3 171 5-5
4 18 100
5 I9 100
6 20 100
7 21 100
s z 22 500
9 .. 123 .4
10 .1 ,. 3 24 1.5
11 .. .. .2 g 25 130
12 ., .. ,2 1 26 .2
13 in , 27 .2
14 25 i 22 w