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VINTAGE RADIO
By RODNEY CHAMPNESS, VK3UG
The magnificent 7-banders from AWA
If ever there was a particular range that stood
out in the AWA stable it was the 7-band radios
of the 1940s and early 1950s. There were quite
a few different models produced and they came
in three cabinet formats – table, console and
radiogram. They were powered by batteries (2V,
135V and sometimes a bias battery) or via a
vibrator (6V) or from 240VAC.
Prior to WWII, people were becoming quite keen on shortwave radio
listening. People loved to hear Bradman making a century at Lords and
shortwave radio was the only way to
hear the tests in England. There was
a proliferation of shortwave transmitting stations and the signals were
definitely better than in the early
30s. Gone also were the difficult to
handle sets of the early 30s, which
didn’t have very good performance
at the best of times, particularly on
shortwave.
Radio receiving principles had become mature by the late 1930s. The
This is an early example of a 7-band AWA mains-powered set. The tuning knob
is on the side of the cabinet.
80 Silicon Chip
superheterodyne receiving principle
using purpose-designed converter
valves, such as the 6A7 and later
types, overcame most of the problems
experienced with the autodyne converter system.
There were also quite a few good
radio frequency (RF) pentodes such
as the 6D6 and its successors. These
valves in particular made the task of
designing a set capable of good RF performance so much easier than it had
been in the past. Also, the problems
with detectors and audio stages had
been solved several years beforehand
with the advent of good, indirectly
heated valves.
Service information on the first
7-banders appeared in the 1940/41
Australian Official Radio Service
(AORS) Manual. It is strange that the
first ones appeared during the war
when domestic radio production was
severely restricted. Probably they had
been designed before the war and
were already in production when war
was declared.
By the time the 7-banders came onto
the market octal valves had largely
replaced the pre-octal valves, even
though many of them were the same
valves with a different base.
So what was it that caused these
sets to really stand out from the
crowd?
First, they had attractive but conservative timber cabinets, not tizzy
like some other manufacturers’ products. The cabinets were well made and
strong. And there was a choice of table
sets, consoles and, ultimately, radiograms, all of which looked the part.
Second, they were quite sensitive,
having a tuned RF stage. Although
RF stages had always been desirable
in receivers intended for long-range
reception, they were not always included due to the extra cost. Where
This restored AWA 617T table set has very
conservative styling. Note the complex tuning dial.
multi-band operation was required,
the extra cost was considerable. These
sets would certainly not have been
cheap.
Third, they covered all frequencies from 540 kilohertz (kHz) to 22.3
megahertz (MHz). This feature was
uncommon on other brands. This
meant that these sets were in demand
as monitoring receivers for the HF
communications were used by rural
fire brigades. A variety of frequencies
were used – eg, during the 1960s,
frequencies ranging from 2160kHz
to 3158kHz were employed by the
Emergency Fire Services of South
Australia.
Other states may have used slightly
different frequencies, with Victoria
using a frequency as high as 3848kHz
for fire front use. A few years earlier
higher frequencies were used – around
the six megahertz area. People in the
outback could also listen to various
Flying Doctor radio stations which
used frequencies from 1600kHz to
around 8830kHz. In addition, they
could eavesdrop on other HF radio
networks.
European migrants bought these
sets too, so that they could hear
broadcasts from home in their own
language. I am led to believe that the
remote opal mining town of Coober
Pedy in outback South Australia had a
large number of these sets. They really
needed a receiver much better than
the norm. The nearest AM broadcast
stations (540kHz to 1600kHz) were
many hundreds of kilometres away
and the shortwave radio stations that
migrants listened to were thousands
of kilometres away.
Sets such as these also caused many
people (like me) to become interested
in amateur radio, as I could hear amateurs on the various radio bands. Amateurs in the 40s, 50s and 60s operated
on AM or Morse code, and the voice
transmissions were easily picked up
This is the rear view of the restored model 617T table set shown at the top of the
page. It features extensive shielding of the valves and IF stages.
MAY 2001 81
on these radios. In fact, some of these
receivers were still being used in this
way into the late 1980s.
Band-spread tuning
Finally, the four highest frequency
bands had the deluxe feature of bandspread tuning which made picking
up remote stations so much easier.
Conventional dual-wave receivers
tuned from 6MHz to 18MHz in one
go, a total of 12MHz, whereas the biggest frequency sweep with the seven
banders is 6.1MHz on the third band
which tunes from 3.6MHz to 9.7MHz.
On the highest frequency band, the
tuning range is 17.7MHz to 22.3MHz,
a sweep of just 4.7MHz.
The dial tuning mechanism has a
reasonable reduction drive and a large
tuning knob. So it is a good receiver
to tune, even on the highest frequency
band. All in all, they were (and are) a
pleasing set to use.
Common characteristics
This unrestored 617C console model
will be an impressive set when the
cabinet is refinished.
AWA had a real winner and cashed
in on the desires of listeners in the
1940s and 1950s. While the AC models were probably much more popular
than the battery and vibrator models,
the latter would have been keenly
sought in remote locations. And while
the battery and vibrator models may
have been a little less sensitive, the
opportunity to put up a larger antenna
in remote areas would have more than
compensated.
All models had about the same tuning range, although the exact coverage
on each band did vary a little.
Cabinet styles varied over the time
that this marque was produced, as
can be seen from the photos. I even
saw one table model in an antique
shop with a leather covering over
the timber.
Alignment difficulties
This is the rear view of the unrestored 617C
console. Note the 12-inch electrodynamic
speaker and its associated transformer.
82 Silicon Chip
The dial mechanism is a bit of a
monster, with the dial being attached
to the cabinet. The band-change
mechanism is connected directly to
the switch but the band indicator is
on the dial scale and is connected via
a cord and spring mechanism to the
band-switch.
AWA recognised the difficulty of
aligning the tuned circuits in the sets
with the dial scale floating around and
devised a method of aligning them
with the dial scale removed. A pointer
is positioned over the edge of the dial
MAY 2001 83
The AWA 7-banders were deluxe sets with band-spread tuning and an RF stage. Some models even had push-pull 6V6GTs in the audio output stage.
This is the front view of an unrestored 805GZ radiogram chassis. Note the
rather elaborate tuning dial.
drum which has a scale from 0-180°
around one half of the periphery. The
alignment details describe how to set
the dial drum at a particular degree
mark and then adjust a designated
coil, etc.
The alignment details are not in the
AORS manuals, with the exception
of volume six (1947) which has sufficient data so that the job can be done
on all models. There are 19 adjustments in the aerial, RF and oscillator
circuits. This is not an alignment task
to be undertaken lightly unless you
have the instruments and knowledge
to do it all. It is a laborious task too.
The intermediate frequency (IF)
is 455kHz. Because of the RF stage,
image problems are not severe, even
on the higher frequencies.
Battery and vibrator models
The battery and vibrator models
were basically the same. In a number
of instances, the only difference was
84 Silicon Chip
whether a vibrator power supply or a
battery cable was plugged into the set.
The first models had a valve line-up
as follows: 1D5G RF; 1C7G converter; 1D5G IF; 1K7G detector and first
audio; 1H4G audio driver and 1J6G
class-B push-pull audio output. The
1J6G is capable of giving 2W of audio
out so even as a battery set it was
capable of impressive performance.
In the table models, a 7-inch speaker was used which would have been
quite effective. However, the 12-inch
speaker in the console models, which
had a decent baffle, would have been
even more impressive.
On batteries, the receivers used a
2V wet cell for the valve filaments and
three series-connected 45V batteries
which gave 135V. Bias was obtained
for individual stages by tapping a 9V
bias battery in the earliest sets. Some
later units only required a 4.5V bias
battery.
One or two models were vibrator
only and due to the way that the filaments were arranged in series across
the 6V battery, it was possible to do
away with the bias battery altogether.
Most battery/vibrator models were
6-valve sets and used the 1J6G as the
audio output.
A few sets used the more conventional 1940s arrangement and had a
1M5G RF, 1C7G converter, 1M5G IF
and 1K7G detector and first audio,
followed by a 1L5G audio output.
Certainly, this would not have had as
much audio sting as the 1J6G but the
current drain would have been less
and the audio would have still been
quite adequate.
The AC models
The RF sections of the AC models
are virtually identical, with only
small variations. The audio stages
are different, depending on whether
the particular set was a table, console
or radiogram model. The table units
were 6-valve sets using a 6U7G RF,
6J8GA converter, 6U7G IF, 6G8G
detector and first audio and 6V6G
audio output.
Console models used the above
valve line-up but I am not sure if in
some instances they had a push-pull
pair of 6V6G valves in the audio
output. The radiograms certainly did
use a more elaborate audio circuit.
A typical valve complement was a
6SQ7GT as the detector and first audio, followed by 6SJ7G phase splitter
and push-pull 6V6G valves in the
audio output.
Some models had a tuning-eye indicator (6U5/6G5) which was mounted
behind a hole in the dial back-plate.
The table and console models have
the chassis mounted hori
zontally,
in the conventional manner. The dial
scale (point
er) moves horizontally
across the dial, with station and frequency markings at right angles to the
scale, as is also conventional.
Mechanically, the radiogram chassis dial mechanism is mounted in the
same way as the table and console
models. However, because the chassis
is mounted so that one end of it is
towards the user (as if mounted vertically), the scale “appears” to move
vertically. Because of the way the
chassis is mounted, the dial markings
are printed in the same plane as the
scale so that they can be read.
Technical details
While there is an oscillator coil
and suitable adjustments for each
frequency range, the same does not
happen with the aerial and RF coils.
If every range had a core and a trimmer for each coil, there would be six
adjustments. For seven bands that
would be 42 adjustments.
As there are only 19 adjustments,
you can assume that some compromises have been made. The complexity of
the receiver in this area can be seen in
the circuit accompanying this article.
There were compromises in the
design and some tuned circuits are
not tuned for optimum performance.
However, any tuning inadequacy is
compensated for by brute force amplification, with six valves instead
of the normal five. It’s not a method I
particularly like but it works.
As mentioned earlier, it is a complex job aligning the tuned circuits so
I’d suggest leaving them alone unless
you really know what you are doing.
Someone that you know may be able
to assist by aligning the set for you if
you feel it is necessary. On the other
hand, the IF stage is quite conventional and can easily be aligned.
In my 617T, I found that the audio
output had noticeable distortion. To
overcome this, I modified the audio
output stage slightly. On the speaker, I earthed the bare wire from the
voice coil to the frame. The negative
lead of C56 was lifted off earth and
a wire connected to it and run to the
insulated wire on the voice coil. A
small connector was placed near the
speaker plug.
This improved the audio quality
noticeably. It can always be put back
to standard if need be.
It seems to me to have been a
mistake that some form of negative
feedback had not been incorporated
in such a quality receiver.
Technical restoration
The components in these receivers
appear to remain in good order after
many years of use. Although the
AWA black “moulded mud” paper
capacitors are considered unreliable,
I’ve found them to be fairly reliable if
there are no cracks in the moulding.
I still replace any critical ones such
as AGC bypasses, the audio interstage
coupling capacitor, the output valve
plate capacitor to earth and RF bypasses on the HT line.
The main area where you hope
to avoid replacing com
ponents is
around the coil and band-switch
assembly. If you do, fine needle-nose
pliers will be essential. The electrolytics should also be checked, although
a surprising number of these are still
in good order in my experience.
The valves should be checked by
replacement if possible. Only rarely
do I need to replace valves, averaging
around one valve per radio restored.
Summary
The AWA 7-banders were a significant series of battery, vibrator and AC
receivers. They were designed to give
the best performance possible over a
wide tuning range. They looked good,
performed well and were easy to operate. They filled an important niche
in the market and some of these sets
are in use even today rather than just
on display as ornaments.
They are not particularly common
as not everyone could afford one, as
they would have been at the top end
of the market. However, because of
the calibre of the sets, it is likely that
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86 Silicon Chip
This under chassis view of an 805GZ radiogram clearly shows the band-switch
details. Note the modification with the old speaker field coil (bottom of chassis).
a greater percentage of the production
run has survived compared to more
common receivers.
They are not an easy set to service
or to align. A complete service would
have been quite expensive. The audio
quality could have been improved
with a slight modification to provide
negative feedback. And although I am
critical of the lack of tuned circuit
adjustments, this does not seem to
compromise the operation.
AWA deemed that these sets had
their day and didn’t produce any new
models after 1950. However, the 617T
appears to have been produced up
until at least 1952.
In 1953, AWA produced a scaled
down version in the 1548MA. This
is a 5-band 6-valve (including tuning
eye) receiver. It has the same tuning
range as the earlier receivers but has
no RF stage. Also, it has the noisy
6BE6 converter so I believe it would
not be anywhere near as good as the
earlier sets.
Hotpoint-Bandmaster also sold
these sets, rebadged with their name.
Overall, there were around 45 separate models with either AWA or
Hotpoint-Bandmaster name badges.
These are a very collectible series
of receivers. My 617T is permanently on display. It is also used as our
entertainment receiver on broadcast
SC
and shortwave bands.
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