The Gramophone Company 519, 509, 470 Service Manual

“His Master’s Voice”

SERVICE MANUAL

fo r

E I GH T-VA LV E

D UA L-WAV E A.C. RECEIVER

Model 470

AN D

DUAL - WAVE A.C. RADIOGRAMS

Models 5 09 and 5 19

TECHNICAL SPECIFICATI ON

VOLTAGE RANGE

200 to 250 volts, 40 to 60 cycles.

It is im portant that the receiver be operated at
the correct voltage; the voltage taps on the mains
transformer should be utilized as follows:

Voltage of A.C. Supply Use Tap Designated

200-220 volts 200
221-240 „ 240
241-260 „ 260

C O N S U MPT I O N Radio Gram

Model 470 .. 105 watts —

Model 509 .. 10 5 „ 165 watts

„ 519.. 105 „ 180 „

WAV E- LEN GT H R ANG E

13.9 metres (21.58 megacycles) to 47 metres
(6.38 megacycles).

187.4 metres (1,600 kc.) to 545 metres (550 kc.).

MAX. UN D IST O RT E D P OW E R

O UT P U T

7 watts.

DI ME N SI ON S

Model 470

„ 509 ..
„ 519 ..

WE IG HT

Model 470

509 ..

„ 519 ..

Height

38*'
34"
34”

cwt. qr.

— 2 18

1 0 6 2 0 0
1 2 13 2 2 20

W id th

27*'
34'

40J'

N ett

lb. cwt

Depth

Gross

. qr. lb.

—

Ι3 Γ
I9 f

20 V

3 10

LOUDSP EAKER

Models 470 and 509 use a 12" speaker, and Model
519 uses a 12* speaker of high fid elity type and very
massive construction, the field winding in each case
acting as filte r choke.

D.C. resistance of field coil, cold 1,200 ohms

D.C. resistance of voice coil:

Models 470 and 509 2 ,,

Model 5 1 9 ............................ 6.3 „

400 cycle impedance of voice coil:

Models 470 and 509 .. 2.35 „

Model 5 1 9 ............................ 8 „

VALVES

6U7G (2), 6J8G, 6G8G, 6B8G, 6L6G, 6H6,

5V4G, 6G5 (Tuning Indicator).

CIRCUIT DESCR IPTION

These models are superheterodynes incorporat
ing a conventional frequency-changing circu it using a
6J8G triode-hexode converter valve. The oscillator
circuit is designed to provide relatively constant
oscillation amplitude over the very w ide tuning range
incorporated in the short-wave band. An R.F. stage
using a 6U7G precedes the frequency changer on

both bands. The I.F. a mplifier has tw o stages, the
first employing a 6U7G and th e second a 6G8G, one
diode of which provides AVC, which is applied to the

R.F. converter, and 1st I.F. stages on both wave
bands. A 6H6 duo-diode follows the I.F. amplifier,
one diode providing signal rectification, while the
other diode is used in the “ Static Lim iter.” The
demodulated signal passes through the Volume
Control to a 6B8G diode-pentode used a s an A.F.
amplifier, which is resistance capacity coupled to a
6L6G beam-type outpu t valve.

The broadcast band aerial coupling is through
a Litz-wound iron core coil of exceptionally high
efficiency. A ll I.F. transformers also employ Litz-
wound iron core coils and silver-coated titanium
oxide fixed condensers, tu ning being accomplished
by axial adjustment o f the iron cores.

I.F. coupling is through the medium of three I.F.

transformers having a total of six tuned circuits, the
firs t and the second transformers having te rtiary
windings which are coupled to the Tone M onitor
switch to provide variable selectivity; broad tuning
is provided in the “ W ide Range” and “ Overseas”
positions of the Tone M on itor, and sharp tuning in
the remaining three positions.

Inductance padding of th e oscillator circuit is

used on the broadcast band; on the short-wave band
no padding adjustment is required. Special close

tolerance fixed padding condensers are used.

Inverse feed-back is applied to the complete A.F.
system, through the Tone M on itor control, from the
secondary of the output transform er to a tap on the
Volume C ontrol; in this way the whole of the A.F.
circuits benefit from the distortion reducing pro
perties of such feed-back. In addition, the circuits
associated w ith the Tone M onitor switch provide
varying degrees of feed-back, differing with fre
quency, thus providing control of tonal balance.
Furthermore, the degree o f feed-back varies with the
setting of the Volume C ontrol in such a way as to
provide the best response fo r both local and distant
reception, and at all volume levels. The speaker

field winding is used as a filte r choke, in conjunction
with tw o 16 mfd. w et type electrolytic condensers,
one of which is of the regulating type. It is essential
that the positions of these condensers in the circuit
shall not be interchanged. The condensers are

mounted on the speaker, and are thus protected

against damage if the speaker plug Is withdrawn while
the receiver is in operation. Jacks are provided at
the back o f the chassis for the connection o f an
extension speaker. They are in the secondary
circuit of the ou tp ut transform er, and are suitable

fo r connection to any loudspeaker having a voice-coil

impedance between 2.5 and 4 ohms (Models 470 and
509 only). An impedance o f 3 ohms at 400 cycles is
recommended, and the speaker should preferably be
of permanent magnet type and requires no trans

form er. The H.M.V. Extension Speaker is very

suitable, and ha s its own constant-impedance Volume
Control.

Model 519 requires an extension speaker having
a voice coil impedance of 8 ohms or more. Such
speakers are not regularly carried in stock; if it is
desired to fit extension speakers to Model 519, the

H.M.V. Service Dept, should be consulted.

CIRCUITS

The circuit diagram of Models 470, 509 and 519,

together w ith all com ponent values, is shown on

pages 4 and 5.

W A V E- B A ND S W I TC H IN G

This is carried o ut by means of a 3-deck switch.
The oscillator primary coils are connected in series
and not switched. A dditional capacitive feed-back
is applied across the padding condenser on the short
wave band, and this is switched by contacts on the
wave-change switch.

In Models 509 and 519, the first position o f the
switch (extreme anti-clockwise) connects the short
wave coils and associated components, and the
second position the broadcast circuits. In Model 470
the switch has a th ird position (extreme clockwise),
in which the pick-up sockets are connected in circuit,
and the radio circuits disconnected.

On Model 470 the VolumeControl is mounted on
the chassis,this being the right-hand control knob. On
Models 509 and 519 the Volume Control is removed
from the chassis and mounted for convenience on
the fro n t o f the cabinet, its place on the chassis
being taken by a “ Radio-Gram” switch.

T O NE MO N I T O R

This is a five-position two-deck switch. The
following effects are secured in the various switch
positions:

1st Position (Wide Range): Bass and treble

boost, and broad tuning, for highest

fidelity.

2nd Position (Norm al): Bass and treble boost,

and sharp tuning. For normal and distant
reception.

3rd Position (Bass): Bass boost and treble cut,

w ith sharp tuning. For deeper tone and
reduction o f static.

4th Positron (Speech): Flat bass response and

tre ble boost, with sharp tuning. For
long-distance reception of speech, or re

duced bass response.

5th Position (Overseas): Flat bass response,

and treble cut, together with broad
tuning. For easy short-wave tuning with
reduced background noise and freedom

from microphony.

The maximum bas s and treble boost, obtained at
low Volume C ontrol settings, is approximately 6db,
but, as previously explained, this is dependent on the

Volume C on tro l position being progressively re
duced towards full volume position.

In Models 509 and 519 a bass boost circuit is

switched into operation in the “ Gram.” position
and is short-circuited in the “ Radio” position.

STATIC LIMITER

This device is controlled by a switch located on
the back of the chassis in the case of Model 470 and
on the control panel in Models 509 and 519. It is
intended to lim it the peak level of static or electrical
disturbances of peaky waveform to a value not
greatly exceeding the level of the carrier o f the

station being received, thus preventing the drowning

of the signal by very loud bursts of static. It is
useful chiefly in long-distance reception of speech,
and in short-wave reception where electrical inter

ference is severe. It usually has a slightly d etri

mental effect on the tone of musical reception, and

should therefore be switched off when not required.
It has no effect on the sensitivity or selectivity of
the receiver.

PR ELIMIN ARY TESTS

(1) Switch on receiver and note that dial lights up

and changes colour when wave-band switch is
operated.

(2) If no signals can be tuned in, remove the shield

from the 6B8G valve and w ith the Volume Con
tro l full on and earth w ire disconnected, touch
the finger to the grid cap o f the valve, when a
loud hum should be heard; this hum should also
be heard w ith wave-change switch at “ Gram”
when the red pick-up jack is touched. This
indicates th at the A.F. side of the receiver is

working, and the fault probably lies in the R.F.
or I.F. circuits. Should no hum be heard, a
fault exists between the firs t A.F. stage input
and the speaker.

(3) Check all valves for heater continuity and free

dom from internal shorts.

DISMANTLI NG

REMOVAL O F C HA SS IS

(1) Remove knobs.
(2) Disconnect speaker plug and power plug.
(3) Remove nuts from tw o fixing bolts from under

side o f shelf; the chassis is now free.

(4) To determine if the fault lies in the loudspeaker,

connect a high impedance A.C. voltmeter or
output m eter, range 0-3 volts approx., to the
voice coil terminals of the speaker. Switch on

receiver, turn Volume Control fully on and tune
across the broadcast band when stations are
known to be transm itting. If meter does not
deflect, the fault lies in the receiver circuits, the
primary o f the output transformer, or in the
field of the speaker. If the meter deflects but
no sound is heard, the speaker voice coil circuit
is at fault.

(5) If the fault is still undiscovered, remove chassis

and speaker from cabinet and compare voltages
with the table given below.

REMOVAL OF LOUDSPEAKER

'(I) Remove 5-pin plug from back of chassis.

(2) Remove fou r screws holding speaker chassis to

baffle and w ithdraw speaker.