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VINTAGE RADIO
By JOHN HILL
Bandspread tune-up for an old
Astor multiband receiver
As readers could well imagine, I have met a
lot of fellow radio collectors over the years,
particularly since I began writing Vintage
Radio. My monthly column has brought about
many meetings and, in some instances, long and
lasting friendships.
However, being a so-called “authority” on vintage radio does have
its disadvantages, including the occasional knock on my door by complete
strangers seeking advice on a particular receiver.
In fact, it was a knock on the door
that started this month’s story although, in this case, the owner of the
receiver is well known to me. Gener-
ally, he is quite capable of servicing
his own radios and can usually track
down an elusive fault and fix it.
In this particular case, the receiver – a 1950 5-valve dual-wave Astor
table model – had been repaired but
the remaining problem was alignment.
Not only was there an annoying double
peak response when tuning but there
was also the matter of three band-
spread shortwave bands that were
badly out of alignment. It seemed as
though someone had tightened up
all the adjustment slugs so that they
wouldn’t fall out.
In a past series of three articles,
I covered receiver alignment fairly
thoroughly but shied away from
multiband shortwave tune-ups. After
three consecutive months devoted to
align
ment, it seemed about time to
change the subject.
However, a multiband receiver
such as this Astor offers different
tune-up problems which should be
discussed. Both the five and 6-valve
versions of these Astors were popular
radios back in the early 1950s and
there are still a lot of them around.
No doubt, a good many of them could
do with a tune-up.
In my opinion, a realignment of this
type cannot be satisfactorily carried
out without a radio frequency generator and an output meter. It was the
owner’s lack of these items that led
him to seek my assistance.
IF transformers
This particular style of Astor receiver was popular in the early 1950s. It was
available in four, five & 6-valve versions, some of which had three bandspread
shortwave bands.
86 Silicon Chip
The first step was to align the
intermediate frequency (IF) transformers, particularly as a double-peak
problem is usually the result of these
devices being out of alignment. Un
fortunately, the IF alignment was not
a straightforward job, as one of the
adjustment slugs was stuck solid. To
make matters worse, the adjustment
slot in the soft iron core had been
gouged out by a screwdriver blade.
Nothing is ever as simple as first
thought!
Tuning the RF generator slowly
across the IF showed up the double
peak, with one peak being stronger
to performance. It is definitely a better
alternative to a double peak.
Broadcast band alignment
The wave change switch in the old Astor is surrounded by a bewildering array
of components & wiring. However, a close examination of the switch will reveal
which coil is in circuit for each switch position. There are eight coils to adjust
plus a trimmer.
The shortwave coils are arranged in two clusters of three. Shown here are
the coils that are switched (one at a time) into the oscillator circuit. The wave
change switch controls a large number of components.
than the other. The strong peak was
at 455kHz while the lesser one was
at 463kHz.
When correcting a problem of this
nature there are a number of options
available: (1) replace the faulty IF
transformer if a replacement is available; (2) add correcting trimmer capacitors to the base connections; or (3)
compensate for the immovable slug by
shifting the ones that will move to the
frequency of the one that has stuck. I
tried the latter option, as it seemed the
easiest solution.
After setting the RF generator to
455kHz, the IF transform
ers were
readjusted to that frequency but there
was no noticeable improvement. Readjusting the transformers to 463kHz
produced a much sharper peak and,
what’s more, without any hint of the
previous double peak. Try doing that
without an RF generator and an output
meter!
Not having a circuit diagram for
the old Astor, I could only guess at
what the IF was supposed to be but
it would be unlikely to be anything
other than 455kHz. While pulling
the transformers off frequency a little
is perhaps undesirable in theory, in
practice it makes little or no difference
The next step was the alignment
of the broadcast band. The Astor is
fitted with a nonadjustable aerial coil,
an iron-dust cored oscillator coil and
a trimmer on each of the tuning capacitor’s two sections. As there were
pointer marks at each end of the dial,
the pointer was adjusted to coincide
with these marks. There were also
marks at 600kHz and 1400kHz for
alignment purposes.
Starting at the low-frequency end of
the band, a 600kHz generator signal
was fed into the aerial and earth terminals and the oscillator coil adjusted
for maximum output as shown on the
output meter. As there was no adjustment provided in the aerial coil, it was
necessary to rock the tuning capacitor
while adjusting the oscillator coil slug
so as to locate the aerial coil peak.
This adjustment did not quite bring
the dial pointer to the 600kHz mark
and so the pointer was slid along the
dial cord a couple of millimetres until
it coincided.
After injecting a signal of 1400kHz
and transferring operations to the other
end of the dial, the pointer was found
to be spot on its designated mark. If
it had not been, the pointer position
could have been moved by adjusting
the oscillator trimmer.
All that remained was to adjust the
aerial trimmer for maximum output
at the 1400kHz position. It too was
almost spot on and the screw required
only a few degrees of rotation to peak
the output meter. This completed the
broadcast band alignment.
Shortwave bands
To the uninitiated, the 3-band,
bandspread shortwave section with
its array of six coils and adjustment
slugs can be rather intimidating.
However, taking one band at a time
removes a lot of the mystery and two
thirds of the coils.
If one looks closely at the wavechange switch, it is not difficult to
work out which pair of coils (three
pairs altogeth
er) are brought into
circuit at each of the three shortwave
positions. It helps if the coils are then
marked: a simple 1, 2 and 3 to correspond to the switch positions is all that
is needed. This is fairly important for
there is nothing more annoying than
April 1994 87
This photo shows the broadcast band coil (the large coil at bottom left) plus the
three smaller shortwave coils that are switched into the aerial circuit.
The three shortwave bands (19, 25 and 31 metres) are marked at the bottom
of the dial. Note the clear frequency markings in MHz for each of these three
shortwave bands.
to move a previously aligned coil slug
by mistake.
These pairs of shortwave coils are
adjusted in much the same way as
those for the broadcast band. During
the alignment procedure, one coil from
a group of three is switched alternately
into the oscillator circuit and its slug
adjusted to give the correct frequency
on the dial. The other three coils are
switched into the aerial circuit and
are adjusted for maximum output.
There are no trimmers with this type
of set up.
In a bandspread receiver, such as
the Astor, three of the more common
shortwave bands were usually cho88 Silicon Chip
sen. They are the 19, 25 and 31-metre
bands. (Note: in a bandspread receiver
of this type, a large fixed capacitor is
connected in series with the tuning
capacitor to restrict its tuning range.
This is designed to make it easier to
select stations without requiring a
large step-down ratio in the tuning
capacitor drive).
19-metre band
Alignment of the 19-metre band
was first. As the dial is also marked
in MHz, a frequency of 15.4MHz was
chosen because it is towards the high
frequency end of the dial. The RF
generator was set to this frequency
and its output injected into the aerial
and earth terminals.
Selecting a frequency of exactly
15.4MHz on an RF generator is a difficult task without some assistance. The
assistance in this instance was provided by a modern multiband receiver
with digital tuning. All one has to do
is tune to the required frequency on the
synthesised receiver and place it near
the RF generator. The RF generator is
then adjusted until a squeal is heard
in the receiver.
By using this technique, almost any
obscure frequency can be dialled up
on the synthesised receiver and the
RF generator adjusted to suit. Receiver alignment on the shortwave bands
can be a hit and miss (mostly miss)
affair unless the generator frequency
is accurately set.
All three shortwave bands required
similar treatment; ie, adjustment of the
oscillator coil slug to bring the frequency in line with the dial graduation,
followed by aerial coil adjustment for
maximum output.
Everything went fairly smoothly
in the shortwave depart
ment, with
no tight slugs to give trouble. The
slug positions were held in place by
re-melting the wax that was originally applied to them for that purpose.
Just re-melting the wax with a warm
soldering iron was enough to shift the
frequency a little and some readjustment was required on one band. It
doesn’t take much to alter the settings
on shortwave adjustments!
If the receiver had been a 6-valve
model with a stage of RF amplification, then there would have been
additional coils requiring adjustment
in the RF section. These would need
to be adjusted for maximum output
after the oscillator and aerial coils had
been reset.
Testing
Testing the receiver was a bit of an
anticlimax. It was midday in January
and there was almost nothing to be
heard on any of the three shortwave
bands. It gave the impression that the
shortwave bands had been completely
detuned.
Fortunately, after-dark reception
was a completely different story and
all three bands responded well to all
corners of the globe. The Astor’s owner
was very pleased.
All things considered, the realignment of the old Astor was a relatively
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An RF generator is indispensable when aligning a shortwave receiver like the
old Astor. The other essential item (not shown here) is an output meter.
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Radio and Electrical Books
Almost any desired frequency can be set accurately on the RF generator with
the aid of this Sangean ATS-803A synthesised receiver. The receiver dial reads
15.4MHz – a convenient alignment point on the 19-metre band. It would be
impossible to accurately set the RF generator to this frequency without the assis
tance of the digital receiver.
straightforward process. On the other
hand, to attempt such a task without
the aid of the RF generator and output
meter would result in far from optimum results.
Alignment fiddles
Many of the valve receivers that we
collect today are getting quite long in
the tooth, this particular Astor being
well over 40 years old. It is unreasonable to expect that someone at some
time in the past hasn’t had a fiddle
with the alignment adjustments. If
they used the right equipment and
knew what they were doing, OK. But
that may not have been the case.
I know from my own early alignment attempts that I’m guilty of mis
aligning many a good receiver. I’m sure
I’m not the only one to do so.
Correct receiver alignment is an absolute necessity if the full potential of
any radio is to be attained. A restoration
is incomplete without a comprehensive
SC
tune-up to finish it off.
1914 Catalog Electro Importing Co ............$18
1936 Radio Data Book ...............................$15
Hammarlund Short Wave Manual (1937)....$11
Henley’s 222 Radio Circuit Designs ......$26.50
Neon Signs (1935) ................................$28.50
How to Become a Radio Amateur (1930) .....$7
How to Build & Operate Short Wave
Receivers ...................................................$18
How to Build a Solar Cell ...........................$11
High Frequency Apparatus (1916) .............$29
Radio for Beginners ................................$6.50
Radio for the Millions .................................$20
Short Wave Radio Manual (1934) ..............$30
Television (1938) .........................................$7
Tesla Coil ....................................................$11
Tesla Coil Secrets .......................................$16
Tesla Said ...................................................$79
Construction of Large Induction Coils ........$23
The Wimshurst Machine How to Make .$19.50
The Wireless Man ......................................$27
Wireless Experimenter’s Manual 1920 .......$31
Electrical Goods & Radio Apparatus ..........$14
Electroplating (1911) ............................$17.75
Experimental Television How to Make ........$34
Meissner “How to Build” Instructions ........$22
How & Why of Radio Apparatus ...........$20.50
All prices include postage. Payment can be
made by cheque or money order made out
to Plough Book Sales, PO Box 14, Belmont,
Vic. 3216. Phone (052) 66 1262.
April 1994 89
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