An overview of the various 7-band models was given in the May
2001 issue. In this article, we'll take a close look at one of the magnificent
console models, the 719C, and the work involved in restoring it to its former
This particular set had had a rough life. It's obviously had
rodents as house guests at some stage and there had also been considerable
cabinet damage due to moisture and exposure to the elements.
With care and patience, it has now been fully restored as shown
in the accompanying photographs. Now I have to admit that I didn't do all the
work - although I am quite happy when it comes to restoring the electronic
circuitry, I am no expert at quality cabinet restoration. So, once I'd removed
the chassis and loudspeaker and dial, the cabinet was passed on to a friend,
Laurie Tilley, whose woodworking ability far surpasses mine.
Removing the parts
Removing the chassis from the cabinet is a tricky job as the
dial-scale/band indicator is attached to the cabinet itself and not to the
chassis as in most sets. This little design quirk leads to other problems, as
will be explained next month in Pt.2 of this article.
It is first necessary to unclamp the dial pointer from the
dial-cord and remove the band-change indicator cable. If this isn't done, it's
possible to damage the dial-drive system. Next, the extension shafts that go
through the right side of the cabinet and attach to the band-change and tuning
control shafts are removed. The dial-lamp cable and the speaker cable are then
unplugged, after which the three knobs on the front panel are removed, followed
by the four bolts securing the chassis.
Because I wasn't restoring the cabinet myself, I also removed
the loudspeaker and baffle-board from the lower section of the cabinet. The
baffle-board is held in place with six wood screws, together with large felt
washers and sleeves. These help prevent cabinet vibrations which could affect
the stability of the local oscillator in the front end of the receiver.
The dial-scale assembly was removed by undoing the four screws
situated at the corners of the assembly. It was then carefully placed to one
side, so that it would not get broken. The whole procedure sounds complicated
but it isn't - just time consuming.
The big clean up
The next task was to thoroughly clean the chassis. As mentioned
earlier, rodents had made their presence felt but fortunately, the damage was
only cosmetic on the outside of the chassis and there was no damage to the
components. Although the exterior is now clean, areas of rust and other
corrosion are evident and do detract from the appearance.
The dial-scale cleaned up like new although there is some damage to some of the markings for the shortwave bands.
As can be appreciated, completely dismantling a set of this
complexity to fully restore the chassis is not something to undertake lightly.
Nor were the owners keen to spend the extra money needed to return the chassis
to pristine condition.
The 50 years of felt-like dust that had accumulated at the
front of the speaker was removed. It is amazing how much dust can accumulate in
a spot that is largely "covered" and is due to the loose weave used in speaker
At this stage, I lubricated all the moving surfaces with light
sewing-machine oil. These parts included the control shafts, dial pulleys,
switches and the dial pointer slide. Many of them had become difficult to
operate due to gumming up and the ingress of dust. All now operate quite
Next, the dial-scale was carefully washed and the dial-pointer
repainted white. Before washing the dial-scale though, I tried washing a small
section of the print in an inconspicuous spot, to make sure it wouldn't come
off. In this case, the print remained in place - unlike some I've tested where
the dial markings are starting to fall off without even touching them.
My advice is to be very careful when cleaning dial-scales on
the side where the print is. If just dusting cleans a dial-scale sufficiently,
don't do any more as dial-scales are hard to replace.
Unfortunately, the dial-scale on this set does have some damage
on the shortwave bands, as is evident from the photograph. This damage was
present before any work was done on the dial and is not due to cleaning.
Apart from this, the dial-scale came up like new. The same goes
for the valves, which were also removed and cleaned with soapy water. When
cleaning octal valves like this, the trick is to keep the them upside down -
that way, the glass envelope can be cleaned without water getting into the
Make sure that the type numbers don't get rubbed off during
this process - clean the valves gently. Clean valves really do look nice when
reinstalled in the chassis.
The AWA 7-banders are extremely good performers and have an impressive cabinet. In this case, the cabinet came up looking like new.
Before really starting a circuit restoration, I like to have a
good look at the set to see what needs attention. It is best to determine early
whether there are likely to be any faults that are expensive to correct, such as
a burnt-out power transformer or any other obviously distressed components. In
this set, some work had been done in the past to replace the original
electrolytic capacitors (the old ones had been left in-situ but disconnected
from the circuit).
I find that a headset magnifier is quite an asset when checking
into the works of a set as complex as a 7-band AWA receiver. They sell for
around $30, while an illuminated magnifier is also available at over $100. I
prefer the headset magnifier. as it is easy to move around the chassis, and use
a lead light of some sort to illuminate the area of interest.
Getting back to the set, most of the black "moulded mud" paper
capacitors appeared to be in remarkably good condition. Conversely, some of the
wiring looked a bit the worse for wear, having perished over the last 50 years,
and this included the high-tension wiring and AC input wires to the power
transformer. In fact, the transformer would definitely need attention before any
power was applied to the set.
Both the mains cord and plug had been replaced at some time but
neither was in good order. What's more, the PVC twin flex cord used was not in
keeping with the vintage of the receiver.
Overhauling the circuitry
The first item to receive attention was the power transformer.
I began by using my 1000V insulation tester to check the integrity of the
insulation between the mains input and earth and to the other windings. The
secondary HT winding was also checked by removing its centre-tap from earth and
then testing to earth. The resistance in each half of the winding was also
checked using an ohmmeter and they were both the same.
Having done those tests to prove that the transformer itself
was in good order, it was time to replace the perished wiring. First, the
terminal location of each wire emerging from the front (or chassis) side of the
transformer was noted on a piece of paper, along with the colour of each
This done, I removed the two mounting bolts from the front of
the transformer and the two bolts which clamp the transformer together, without
removing the transformer from the chassis. The front covering plate was then
removed so that the high-voltage wiring was exposed. Each wire was then
individually removed from its termination and replaced so that no wiring errors
could occur. The transformer was then reassembled.
The next step was to replace the leaky paper capacitors. As
mentioned earlier, most of the black "moulded mud" paper capacitors were quite
OK when tested with the high-voltage tester. However, some had previously been
replaced with Ducon capacitors which had now gone leaky and these were all
The resistors were all within tolerance and none required
As mentioned earlier, the mains cord fitted was not in keeping
with sets of this vintage. As a result, I decided to fit a new 3-core brown
fabric-covered mains lead, which would be similar to the style of lead
originally fitted. The mains plug was in poor condition and so this too was
replaced. I used a modern plastic plug and although it doesn't have a vintage
appearance, it is safe.
Fig.2: the set employs a 6-valve superheterodyne circuit with a multi-pole rotary switch for the band switching. Alignment is a complicated procedure but is necessary for top performance.
The chassis-entry grommet for the mains lead had perished, so
this too was replaced. In addition, the lead was securely clamped to the chassis
- it's no longer permissible to tie a knot in the power lead after it enters the
chassis, as was common some 50 years ago.
As a further safety measure, the earth lead of the power cord
was soldered to a lug which was securely bolted to the chassis. As originally
manufactured, this set didn't have an earth wire in the mains lead and the
chassis wasn't earthed.
The dial cord was also the worse for wear, so a new cord was
fitted. Fig.1 shows how this is done. The original 1mm-diameter (approx.) dial
cord required two turns around the dial driveshaft to ensure an effective grip.
However, I generally use 0.7mm cord so I put three turns on the dial driveshaft
just to make sure.
This works well and the dial mechanism is much freer than on
many sets I've come across. It even has a flywheel on the drive shaft so that
the set can be rapidly tuned from one end of the dial to the other.
A number of the insulated wires within the set had perished, so
these were replaced one at a time. Finally, a check was made with an ohmmeter to
verify that there were no short circuits, particularly on the HT line. This all
checked out, so it was time to start the testing procedure.
Firing the set up
Power was initially applied to the set with all the valves
removed. The AC voltages out of the secondary of the transformer were then
checked and found to be a little high. This was to be expected because, with the
rectifier valve removed, there is no load on the transformer. I let the set run
like this for about 30 minutes and the transformer stayed cool, indicating that
it was in good order.
The set was then turned off, the rectifier and speaker plugged
in, and the mains switched on again. The HT rose to nearly 500V, which is normal
with no load in these receivers. The set was then switched off after a few
seconds and the electrolytics allowed to discharge.
This was done several times to "form" the electrolytic
capacitors and they remained cool during this procedure. The time taken to
discharge increased with each on/off cycle, indicating that the capacitors had
"formed". Being relatively modern capacitors, they appeared to be quite OK right
from the word go.
There's plenty of room in the back of the cabinet for the chassis. The loudspeaker fits in the cabinet immediately beneath the chassis shelf and is just visible at the bottom of the picture.
By the way, it's always a good idea to go through this routine
as the electrolytic capacitors may be badly in need of "forming". If the HT is
simply applied and left on, the capacitors may overheat and explode. They may
also cause the rectifier to be severely overloaded. However, short term
overloads rarely cause a problem and the capacitors will usually quickly
At this stage, all the valves were replaced in their sockets
and the set again turned on. A quick check with the multimeter revealed that all
voltages were nominally correct. However, after some time, the HT decreased due
to the fact that the 5Y3GT rectifier had come to the end of its useful life. A
replacement valve soon fixed that problem.
Next, an aerial and earth were connected to the receiver, as it
was time to tune around and see whether the set was in working order. I switched
to the broadcast band and found a number of stations. 3GG on 531 kHz is a good
test where I live, being a 5kW station with a directional antenna some 200km
away. If the signal is loud and clear from this station, I know that the set
being tested is in good order.
There was one problem - the tuning gang mounting grommets had
perished and so the gang wobbled around. Unfortunately, unless the coil
sub-assembly is dismantled (a major job), it isn't possible to directly replace
To get around this problem, I began by cleaning all the
hardened rubber out from around the two mounts near the dial drum. I then slit a
gang-mounting grommet through its slot, so that I ended up with two rubber
washers. These were then cut so that they could be opened out and slipped around
the metal gang mounting posts near the dial drum
A small screwdriver to was used push each half-grommet under
each flat near the metal mounting posts. They were then secured in place by
applying some glue to their outside edges and the chassis. Each half-grommet now
provides some support for the gang and there is some give on the mount.
Alignment is quite a task with the AWA "seven-banders" and the
719C is no exception. In fact, I gather that most owners of these sets tend to
shy away from aligning them and I can't say I blame them.
That said, they are excellent sets and it really is well
worthwhile going through the alignment procedure, to get the best out of them.
I'll walk you through the alignment steps in detail next month.
Assembling the receiver
While I'd been solving the circuit problems, Laurie Tilley had
been restoring the cabinet as near as practical to its original condition. It
looks good, as the photograph shows, and the owners are happy with the their
Once the cabinet had been returned, the speaker and baffle were
replaced and the six 50mm mounting screws (along with the felt washers and
sleeves) were installed to hold the baffle in place. It really is quite an
elaborate system to ensure that baffle vibrations are not transferred to the
oscillator tuning components and thus cause instability.
The dial-scale and then the chassis were also refitted to the
cabinet. The dial-scale has four small screws and the chassis has four larger
metal thread bolts holding it to the cabinet shelf. The dial-scale clamp was
then reattached to the dial cord and the band-change bowden cable was reattached
to the band-change drum.
The position of the bowden cable within its clamp allows for
some adjustment of the band indicator behind the dial glass. Finally, the
extension shafts for the band-change and tuning controls were installed, the
knobs fitted and the loudspeaker reconnected.
I timed myself doing this job and it takes almost 30 minutes.
This included adjusting the dial pointer position and the band-change indicator.
As a matter of interest, I later tested myself on a much simpler Precedent
mantel set and it took me just 60 seconds to do what had taken half an hour on
the AWA set!
Once the assembly had been completed, the set was given a final
performance check to make sure everything was OK. The clamp on the dial-cord was
then adjusted so that the stations appeared in their correct positions on the
By this stage, the set was going nicely and I was admiring the
cabinet and its performance when it suddenly stopped working. So what had gone
The grid of the first audio stage (6G8G) comes out to a top cap
and so, using a time-honoured technique, I touched it with my finger - all I
heard was a thin squeak rather than the expected healthy "blurt". I tried
another 6V6GT audio output valve but it made no difference. And that meant that
the set had to be dismantled again, so that I could find out where the fault
Once I had it dismantled, I tested around the audio section and
found no problems. Then a small sliver of wire fell out of the wiring - a
leftover from a snipped component lead. Perhaps it was this that was causing the
problem but, despite shorting various sections, I couldn't reproduce the
symptoms originally observed.
In the end, I concluded that this had to be the answer so the
set was reassembled. It worked well for a while - then stopped again. I advanced
the volume control and the set suddenly burst into life. This is usually a sign
of a bad connection somewhere, either a dry joint or a corroded or poor joint
inside a component. At least I was starting to narrow down the source of the
It was time to get serious about finding the problem. Often,
with intermittent faults, the best approach is to connect the appropriate test
equipment and then just wait for the fault to show. In this case, I connected my
DMM (set to the 400V range) to the plate of the 6G8G, to measure the plate volts
under normal and fault conditions. I also connected an audio signal tracer to
the grid of the 6V6GT to see if audio was getting this far without trouble.
Note: for safety reasons, it is necessary to switch the set off when changing
the test instrument test points.
Next, I adjusted the volume controls (at low level) on both the
set and the signal tracer for the same volume. After a while the set went quiet
but the test instruments showed no change.
I then connected the DMM to the plate of the 6V6GT and
connected the signal tracer to the same spot. When the fault reappeared, the
plate circuit of the 6V6GT was still operating correctly, with both the voltage
and the audio the same as before the fault.
I then moved the speaker and the fault came and went (this had
had no effect previously). Careful inspection using the headset magnifier
revealed a dry joint on the hum bucking coil on the speaker. The joint was
resoldered and the radio now operates reliably for the first time in 50 or so
As mentioned, aligning this receiver can be quite a chore. The
"7-banders" are all slightly different in their alignment details and dial
glasses, which means that the precise details for a particular model are needed
if accurate alignment is to be achieved.
Unfortunately, very little alignment data is available, except
in Volume 6 of the AORSM manuals. However, I have been thoroughly frustrated by
the published alignment instructions and the errors that have crept in.
In the end, I developed a method that is relatively easy and is
as accurate as possible for all models.
The AWA 7-banders are expensive receivers to service,
especially if you want to achieve the best performance possible. The performance
is (as expected) extremely good and the cabinet is impressive and really looks
the part in the lounge room.
The tuning range covers 530kHz to 22.3MHz in seven bands. It
has bandspread on the higher frequency bands and has a tuning mechanism that is
very free, which makes tuning a dream compared to a normal dual-wave set
covering nearly the same tuning range.
In summary, the AWA 719C console is a highly sought-after
radio, with impressive performance, ease of tuning and a high price tag. If you
have the room to display one of these radios, go for it.
The Tasma Model 22, manufactured by Thom & Smith, Sydney, in 1931 is a 3-valve TRF receiver. It used the following valves: 224 detector, 247 output and 280 rectifier. (Photo and information courtesy of Historical Radio Society of Australia).
Airzone Model 300: Manufactured by Airzone, Sydney, in 1934, the Model 300 is a typical Australian "cathedral" style set. It is a 4-valve superheterodyne set with the following valve types: 57 autodyne mixer, 50 amplifier, 59 anode bend detector/output and 80 rectifier. (Photo and information courtesy of Historical Radio Society of Australia).