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VINTAGE RADIO
By RODNEY CHAMPNESS, VK3UG
The HMV 660 console of 1940
Housed in a stylish cabinet and boasting
performance to match, the HMV 660 was
undoubtedly one of the better console
receivers from the early 1940s. It is a 5-valve
dual-wave receiver that’s well-made and
easy to service.
These days, our homes are crowded
with electronics equipment, including
VCRs, DVD players, large-screen colour TV sets, audio and home-theatre
equipment and of course, transistor
radios. However, in the early days
of electronics, the average home of
the 1930s was lucky to have just one
radio receiver.
At the start of the 1930s, this would
probably have been a TRF receiver
of mediocre performance coupled
to a large outside antenna and earth
system. Later, when superheterodyne
receivers became established, large
mantel and table sets became more
common, while the more affluent
lashed out and purchased a console
receiver costing many “guineas”.
What’s a “guinea”?
The large, easy-to-read dial was an impressive feature of the HMV 660 console.
80 Silicon Chip
For those born after the abolition
of pounds, shillings and pence, a
guinea was equal to one pound and
one shilling (a pound was equal to
two dollars when decimal conversion
was introduced at the start of 1966).
So why was the term “guineas” used?
Well, it always sounded so much
more upmarket (or “toffy”) than
pounds and shillings and it also had
the advantage, at least from a salesman’s point of view, of making the
price sound less that it really was.
Racehorses were always sold in guineas, for example, so why not upmarket
radio receivers?
The console receiver held pride of
place in the lounge room right through
the 1940s but waned in popularity
in the 1950s when radiograms took
over. In turn, radiograms were relegated to second place when TV was
introduced.
During the heyday of the console
receiver, many fine examples were
manufactured. Recently, I was given
the opportunity to closely examine a
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“His Master’s Voice” logo is still on
the top of the cabinet.
This particular cabinet is in very
good condition and has not been
stripped back. However, a few marks
are visible and they will be polished
out in due course. In fact, Laurie prefers to keep the cabinets looking as
original as possible and a few minor
blemishes are allowed to remain.
This brings us back to the old argument as to whether a receiver should
be restored to “as new” condition or
simply made look to respectable and
restored to good working order, while
keeping it as original as possible. Much
depends on the sets themselves, some
of which may be 70 years or more old.
And, of course, individual restorers
will have their own ideas.
A glance inside the back of the cabinet reveals the battleship-grey chassis
and chassis-mounted components that
were typical of HMV sets. Everything
looks solid and neatly laid out. The
loudspeaker is a 12-inch (305mm)
HMV electrodynamic unit attached
to the substantial baffle board in the
lower section of the cabinet.
Guarantees and instructions
This view inside the cabinet shows the quality of the construction. The envelope
to the left of the chassis contained the original instructions and the guarantee.
An interesting aspect of this old
HMV 660 is that the installation and
operating information, along with the
guarantee card, were still with the set
when Laurie obtained it. This is very
HMV 660 owned by one of my friends,
Laurie Tilley.
Cabinet style
The HMV 660 was one of the better
quality units available on the Australian market around the start of the
World War II. It is an extremely solid
(heavy) unit made from high-quality
plywood and has an attractive veneer
on the outside surfaces.
The half-round dial-scale on these
receivers always impressed me,
perhaps because I liked seeing my
grandfather’s HMV 660 set. I used to
be fascinated by the colourful lighting of the dial which, to an 11 year
old boy, was very impressive. This
model is claimed by some to be the
best console made by HMV and probably one of the best of any makes for
that matter.
The cabinet has a walnut finish with
figured walnut inlays on the front
and is a well-made, quality item. The
original HMV decal with the familiar
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This view shows the partially-restored chassis. The power cord (far right) had
badly perished and was still awaiting replacement when this photo was taken.
February 2004 81
unusual, as most of these “extraneous”
bits and pieces never survived more
than a few years. Today, these items
and the packing cartons are often
considered to be more valuable than
the sets themselves.
The accompanying photographs
give will you some idea of the contents
of these documents, which make fascinating reading. If you are fortunate
enough to obtain a receiver with any
(or all) of the literature and accessories,
be sure to keep them, as they too are
part of our radio heritage.
Fig.1: the HMV 660 is a fairly conventional 5-valve superhet receiver. Note that this set
has three IF transformers – two before the 6U7G IF amplifier valve and one after it.
Dismantling the set
82 Silicon Chip
Dismantling the set is a straightforward task. First, the four knobs are
removed and all except the tuning
knob have screws which go through a
slit in the control shaft. HMV appeared
to be the only manufacturer that did
this at the time. It has the advantage
of placing minimal pressure on the
bakelite knobs while still retaining
good rotational ability. In fact, I haven’t
seen a single broken knob where this
technique has been used.
Once the knobs are off, the celluloid
strip labelled with the control functions, is removed from the shafts, along
with the felt shaft washers. The two
long (6mm diameter) bolts that attach
the chassis to the chassis shelf are then
removed, after which the speaker lead
can be unplugged and the chassis slid
out from the back of the cabinet.
Once it’s out, the chassis can sit on
one end quite comfortably for servicing or you can use a servicing jig such
as the one described in the October
2000 issue of SILICON CHIP.
Laurie has not found it necessary to
replace many components at this stage,
apart from the electrolytic capacitors
and the power cord. If you want to
keep old sets looking original, by the
way, 3-core (brown) fabric-covered
power lead is available from Direct
Components, PO Box 437, Welshpool,
6986 (phone 08 9479 4850); and from
Elizabeth Trading, 15 Station St (PO
Box 374), East Kew, 3102 (phone 03
9859 8799).
In addition, one bypass capacitor
earth lead has come adrift from its
mounting lug but everything else was
in quite reasonable condition. The remaining components will be checked
further at a later date, with emphasis
on the critical audio coupler and AGC
bypass capacitors. The speaker cloth
was replaced with a plain brown cloth
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and although it doesn’t have the same
pattern as the original, it doesn’t look
out of place.
The dial system still works well,
with no slipping. As mentioned earlier, this is an impressive set to look at
from the front and equally impressive
in its build quality when viewed from
the rear.
Circuit details
HMV receivers of this era have
always impressed me with their attention to circuit detail. The HMV 660 is a
5-valve set with a 6J8G converter. This
is followed by a 6U7G IF amplifier on
457.5kHz, a 6B8G as a combined diode
detector, AGC diode and pentode audio amplifier, and then a 6V6G as the
audio output stage. The power supply
uses a 5Y3G as the rectifier.
Let’s first take a look at the front end.
This radio is a dual-wave unit, covering 550-1600kHz on the broadcast
band and approximately 6.4-21.6MHz
on the shortwave band. Due to the
smooth dial-drive system, shortwave
stations are fairly easy to tune in.
The dial-scale is illuminated by four
lamps but only two at a time are used,
depending on whether the broadcast
or shortwave band is selected. As a
result, only the appropriate section of
the dial scale is illuminated.
The connections to the antenna
system are rather unusual. As shown
on the circuit diagram (Fig.1), the
“earthy” end of the antenna coil goes
to an unearthed antenna terminal (A1).
This manual was also inside the large
envelope. It describes how to install
and operate the receiver and covers
both the 660 and 550 models.
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The HMV 660’s original guarantee form and registration card were inside the
large envelope that was adjacent to the chassis. It’s rather unusual for this type
of printed material to survive intact,
This is normally bridged to the earth
terminal, so why have this terminal at
all if it is earthed out anyway?
The answer is that for normal operation, the additional terminal is
superfluous. However, on shortwave,
the performance can be considerably
enhanced if the A and A1 terminals
are connected to a balanced 75-ohm
transmission line which terminates
on a horizontal dipole antenna. Note
that, for best performance, the dipoles
need to be cut to suit the particular
bands of interest.
Apart from the unusual antenna input circuit, the antenna coils are quite
standard for the time. The primary
windings of both antenna coils are in
series with each other, which saves
one switch position. L5 has so little
inductance that it doesn’t affect the
operation of L1 and, in fact, acts as a
small loading coil to slightly improve
broadcast band performance.
Conversely, L1 looks like a large RF
choke in series with L5 when the set
is tuned to shortwave. However, this
has no effect as the shortwave signals
are passed through capacitor C1 with
very little attenuation.
L1 and C1 together form a resonant
circuit which resonates at a frequency
just below the broadcast band. This
increases the performance at the lowfrequency end of the dial and the loop
at the top of L1 improves the coupling
at the high-frequency end.
The IF (intermediate frequency)
amplifier stage is more elaborate that
in most sets of the era. As shown on
Fig.1, there are two IF transformers at
the input of the IF amplifier and one
after it. The type of coupling used is
called “shunt capacitance coupling”
or “bottom coupling”.
The two transformers at the amplifier input are designed to give a response
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This under-chassis view shows the open layout around the wave-change
switch and the coils. Other sections of the receiver follow in a logical circuit
progression from the top righthand corner, down the side and along the bottom,
with the power supply down the lefthand side. The chassis was designed for
more than one model, judging by the plates used to cover several spare holes.
curve that has a slight dip in the centre
at 457.5kHz and a reasonably sharp
cut-off outside the pass-band. Taken
together, the IF transformers give a
substantially flat response right across
the pass-band. This added complexity
results in an audio frequency range
out to 8-9kHz, as compared to around
4-5kHz in most other sets.
So the HMV 660 was indeed a quality receiver!
A comment in Vol.4 of the “Australian Official Radio Service Manual”
(AORSM) stated that one of the tone
control positions was designed to
boost the high-frequency audio output
to make up for the sloping response
of the IF amplifier. So it appears that
HMV made every effort to produce
high-fidelity audio output from their
receiver. And although we may not
consider 8-9kHz as hifi today, it certainly was back in 1940!
84 Silicon Chip
The circuitry following the 6U7G
IF amplifier is conventional, with the
6B8G providing delayed AGC and diode detection. AGC is applied to the
6J8G converter stage and the 6U7G
IF amplifier, while around half this
amount is applied to the audio amplifier. This is designed to ensure that the
set produces an audio output that’s at
the same volume for both strong and
weak stations.
An undesirable byproduct of AGC
can be a high level of noise when tuning between stations. This could have
been overcome by using extra circuitry
to partially mute the receiver between
stations. However, because this increases the complexity and therefore
the cost, it was rarely done.
The audio amplifier
The detected audio output is applied to a tapping on the secondary
of the final IF transformer (IFT3).
From there, it is then fed through an
IF filter network (C21, R11 & C23)
and a volume control to the grid of
the 6G8G first audio amplifier stage.
The resulting signal is then applied
to the 6V6G, which in turn drives the
12-inch 2-ohm loudspeaker via output
transformer T1.
Note the resistive divider consisting
of R22 and R23 across the secondary of
the speaker transformer. This applies a
feedback signal via the switched tone
control network to a tap on the volume control. This was a very effective
method of tone control and provided
good quality sound with minimal
distortion (for those times).
The chassis is also wired so that
a record player pick-up can be connected to the audio output stages,
just ahead of the volume control (ie,
at P.U.). In practice, the pick-up leads
were plugged into two banana type
sockets on the rear apron of the chassis. Note that the earth socket is split
so that when the plug is inserted, the
junction of R11 and C21 is earthed,
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thereby shorting out the audio from
the receiver’s detector stage.
This was a neat system that obviated
the use of an additional switch section
to switch off the HT voltage to the converter and IF stages. However, it didn’t
remove the AGC voltage from the
6G8G, so variations in volume could
be expected if the set was tuned to a
station that was fading and causing the
AGC voltage on the 6G8G to change.
In practice, this really wasn’t much of
a problem as most people listened to
local broadcast band stations where
fading didn’t occur.
The pick-up inputs were probably a
selling point but you have to wonder
how many people actually took advantage of them by connecting a turntable.
Probably very few!
The power supply
The power supply is quite conventional, the only minor variation being
that the field coil (filter choke) in the
electrodynamic speaker is placed in
the negative lead. This meant that the
coil winding and the earthed frame
had very little voltage between them,
ensuring very little insulation stress.
The back bias and delayed AGC voltage is obtained by tapping off part of
the voltage developed across the field
coil via a voltage divider network.
Under the chassis
The view under the chassis shows a
neatly laid out set using small groups
of components which are mostly soldered onto insulated mounting boards.
Access is quite good and restoration is
not a problem. It really is a pleasure
to work on such a well laid out set.
Alignment
Unfortunately, the AORSM does not
give any information on aligning this
receiver. However, the procedure for
aligning the signal input and oscillator
circuits will be quite conventional, as
described in the article in the February
2003 issue of SILICON CHIP.
The alignment of the IF amplifier
stage may require a different technique
to that commonly used. I have not had
an opportunity to align this set and
Laurie hasn’t found it necessary to do
so either, as the set is already performing quite well.
Should alignment be required, the
secondary of IFT1 should be loaded
with a 10kΩ resistor when its primary
and IFT2 are being adjusted. Similarly,
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The HMV 660’s manual is well written and contains detailed notes on both the
installation and operation of the receiver. It even explains the procedure for
connecting an external loudspeaker.
remove the 10kΩ load and place it
across IFT2 when adjusting the secondary of IFT1. By using this method,
you should have a good chance of
successfully obtaining the correct IF
transformer response shape.
IFT3 can be aligned in the usual
manner, as discussed in the articles
in the December 2002 and January
2003 issues.
Summary
In summary, the HMV 660 is an
impressive 5-valve dual-wave receiver
with better than average performance.
To match this performance, it is in-
stalled in a solid, well-made console
cabinet.
Despite its age, Laurie found that
it required very little work on the
circuitry to restore it to good working
order. The dial is particularly impressive, both in terms of looks and performance. It’s a well-made unit with
little sign of wear in the mechanism,
despite its age.
Finally, this is an easy set to service,
particularly when compared to many
other sets. The only thing you have to
watch out for is the method of aligning
the IF transformers, to get the correct
SC
pass-band response.
February 2004 85
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