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VINTAGE RADIO
By RODNEY CHAMPNESS, VK3UG
The AWA PF 11B-6V car radio
and the Ferris “Tranimate”
We often think that transistorised radios are a
fairly recent innovation. However, solid-state
equipment has been around in reasonable
quantities since the late 1950s or almost half
a century! As a result, many transistorised
receivers now fall into the “vintage” category.
The two items described in this
article certainly fall into that category.
For example, the AWA PF 11B-6V car
radio was a mid-1960s all-transistor
receiver, that was available in two
models: a “standard” model with
a single-ended audio output and an
up-market unit with a push-pull audio
output stage.
The other unit to be described is
the Ferris “Tranimate” which, to the
best of my knowledge, was a unique
Australian innovation. In the 1960s,
dedicated car radios were expensive
“add ons” and this little device was
intended to allow an ordinary household transistor portable to function
as a cheap but effective car radio. A
car radio antenna was installed on
the car, with its coaxial lead plugged
into the Tranimate. The output from
the Tranimate was then coupled to the
portable radio and bingo – you had a
cheap car radio.
AWA VW-1200 car radio
There are lots of people involved in
restoring old cars, often to “as-new”
condition – and in many cases, better
than new. And of course, they want the
radio that’s installed to look and work
just as it did many years ago.
As a result, I’ve recently been
involved in restoring several car radios for vintage car enthusiasts. The
jobs are not always straightforward
though, since car radios are usually a
bit more of a challenge to restore than
“bog-standard” 5-valve AC mantel radios. That’s mainly because car radios
are more compact and so are harder to
access than domestic receivers. They
have also invariably had a rougher
life and are usually better performers
than metal receivers, which means
that you have to know how to get the
most out of them.
Still, it’s always interesting to
restore these old radios and it helps
me recoup some of the outlay for my
hobby.
I’m not too sure how the Volkswagen
driver found me – he simply turned
up one day and asked me if I could get
his 6V AWA car radio going properly.
It was operating but only just – the
stations that could be picked up were
very weak and the set had quite a bit
of noise in it.
Well, it looked like an interesting
project and as luck would have it,
I already had a circuit for the 12V
version of the set (it’s very similar to
the 6V version). I don’t like tackling a
restoration job without a circuit diagram if at all possible, since the job is
always so much quicker and easier if
you have the circuit details.
Opening up the receiver
This old AWA car radio receiver cleaned up quite well and will certainly
look the part inside the restored Volkswagen. Note the press button tuning.
80 Silicon Chip
The first step was to remove the
cover (shield) from the set and this is
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The PC board is mounted upside down inside the chassis but is quite easy to
detach and “swivel” away from the finned heatsink. Note the large preset tuning
mechanism.
done by removing 12 screws around
the top of the case and lifting it clear
(car radios are shielded to minimise
external interference). This reveals
a sheet on the inside of this cover,
showing the locations of the various
transistors and the alignment points on
the PC board. This sort of information
is always very useful when it comes
to servicing the set.
As shown in the above photo, the PC
board is mounted upside down inside
the case with its track side facing upwards. In order to gain access to the
component side, it is necessary to first
“spring” a couple of clips along the
front edge of the PC board. That done,
the front edge of the board can be lifted
up and moved forwards slightly. This
disengages the board from slots in the
heatsink and its back edge can then be
swivelled up.
Once it’s out, it would be quite
easy to short parts of the board to the
earthed metal clips that hold the board
in place. As a result, I placed a layer of
thick cloth between the board and the
clips to prevent this from happening.
I than took a look at the various stages
inside the set but could see nothing
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that was obviously wrong – ie, no
broken wires, overheated components
or the like.
Audio stage troubleshooting
My next step was to connect the
receiver to a 6V DC regulated supply
capable of delivering up to 3A.This
coped quite easily, as the receiver’s
drain is just 1.2A maximum. I then
connected an antenna to the set and
plugged in a 16-ohm loudspeaker.
When it was turned on, it behaved
just as it did in the car. The reception was so noisy receiver that it
was a struggle to pick out any of the
stations. However, this noise was
still there when the volume control
was turned down, so that part of the
problem certainly didn’t involve the
RF section.
Next, I installed a 1000µF electrolytic capacitor across the base to emitter
junction of the 2N408 transistor in the
audio output amplifier and the noise
disappeared. Because the audio amplifier is direct coupled, I reasoned, incorrectly as it turned out, that the 2N408
was noisy (this can be a problem with
germanium transistors). I didn’t have
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A piece of cloth was placed underneath the PC board
to prevent shorts to other components when power
was applied during servicing
any 2N408 germanium transistors,
so I fitted a BC558 silicon transistor
instead. The transistor worked OK but
the noise was still there.
It was then that I spotted an electrolytic capacitor that was starting to
bulge at one end. This too was replaced
but rather surprisingly, it made no
difference.
What next to try? First, resistor R20
needed to be replaced with a lower
value, so that the BC558 I had substituted (and the other stages) would be
biased correctly. The original resistor
was 15kΩ (remember this is the 6V
version of this receiver), so I replaced
it with a 10kΩ resistor. And would you
believe it? – the noise disappeared.
So I had jumped to the wrong
conclusion that the old germanium
transistor was noisy. In fact, I should
have woken up to this when I first
82 Silicon Chip
tried the electrolytic capacitor across
the base-emitter junction. The audio
stage now performed as it should,
with quite good gain and just a slight
background hiss, so I was half-way
through fault finding.
RF stage repairs
Checking the front end wasn’t quite
as easy, not that direct-coupled audio
stages are always a joy to work on.
The set couldn’t receive any stations,
so I decided to begin by checking the
intermediate frequency (IF) stage.
To do this, I first connected a 10nF
ceramic capacitor in series with the
output of an RF signal generator. The
RF generator was then set to 455kHz
and its output fed, in turn, to various
points of the IF amplifier. However,
the output levels varied according
to where the probe was placed, due
to the capacitive voltage divider and
the heavy loading I was placing on the
tuned circuits with the crude probe I
was using. As a result, there was no
clear-cut indication of the performance
of the IF amplifier.
Next, I fed the RF generator’s signal
into the base of the converter (VT2)
and carefully aligned the IF amplifier
stages. This noticeably improved the
performance of this stage but the receiver was still having trouble picking
up stations.
By now, I was beginning to think
that the converter wasn’t converting
the signal frequency to the IF (intermediate frequency). To test this theory,
I tuned the set to the low-frequency
end of the dial and then tuned another
receiver to 1200kHz and placed its
antenna lead adjacent to the car set’s
converter stage. I then tuned the car
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radio upwards from 530kHz and was
greeted by noise quietening as the car
radio’s oscillator went past 1200kHz.
So the oscillator was working and
hence the converter probably was
too. But there was still no sign of
stations!
I then did some measurements
around the RF stage and found that
there was 6V on the collector of this
transistor instead of 0V. The cause
wasn’t hard to find – RF choke L2 was
open circuit! A quick hunt around my
workshop soon turned up some small
Dai-1Chi 5mH RF chokes that I had and
I fitted one into the receiver. And that
was it – the collector voltage on the RF
transistor dropped to 0V and the set
burst forth into glorious sound.
Now that the set was operating
properly, all that remained was to
align the front end and give it a good
clean up. The oscillator alignment was
already correct but trimmer capacitor
C7, which peaks the RF stage at the
high frequency end of the tuning
range, had been adjusted for maximum
capacitance and was difficult to move.
In fact, it appeared that the trimmer
didn’t have enough range to peak the
alignment of this stage. This problem
was solved by connecting a 10pF NPO
ceramic capacitor in parallel with
the trimmer (under the board), after
which I was able to peak the RF stage
alignment.
Final peaking of the RF and oscillator stages is carried through a hole
in the base of the set once the metal
cover is back in place. In particular,
the antenna circuit cannot be peaked
until the receiver is in the vehicle and
attached to the fully extended antenna.
To do this, the set is tuned to a weak
station at around 1500kHz and the
flat knob on the underside of the set
is rotated until the best performance
is achieved.
Cleaning up
Having got the set working correctly,
I then proceeded to clean up the case
as much as practical. The knobs were
washed in the laundry sink in soapy
water and I used a small nail brush
to remove the dirt from between the
ridges in the knobs. In addition, the
two smaller knobs had peeling black
paint in their centres so I put a small
amount of flat black enamel paint on
them to make them look original.
The case itself had a couple of pieces
of masking tape and other bits of muck
www.siliconchip.com.au
Photo Gallery: Peter Pan Model
BKJ 5-Valve Receiver
Housed in a stylish wooden cabinet, the Peter Pan BKJ was a 5-valve dual-wave
mantel receiver which covered the medium-wave (broadcast) and the 5.88-18.75MHz
shortwave bands. It was manufactured around 1946 by Eclipse Radio Pty Ltd (Melbourne) and used the following valves: 6J8-G frequency changer; 6U7-G IF amplifier;
6B6-G detector, AVC detector and first audio amplifier; 6V6-G audio output; and 5Y3-G
rectifier. (Photo courtesy Historical Radio Society Of Australia (Inc.).
stuck to it which I scraped off. I then
used a eucalyptus-soaked rag to clean
the case and the front panel. A kitchen
scourer was then used to remove some
of the more stubborn marks although
this was done rather gently because
I didn’t want to destroy any of the
wanted markings on the case.
In the end, both the case and the
front panel looked quite good, although they still weren’t exactly in
pristine condition.
Brief circuit details
OK, let’s now take a brief look at the
circuit details of this AWA car radio
receiver – see Fig.1. As shown, the
antenna input is a typical car radio
input circuit, where the capacitance
of the coaxial cable from the antenna
forms part of the tuned circuit. That’s
why the antenna circuit cannot be
peaked for best performance until
the set is installed in the car. Note
that the actual tuning of this and the
following stages is done by a variable
inductance tuner.
Transistor VT1 amplifies and
applies the signal through another
inductance tuned circuit to an autodyne mixer/converter stage based on
transistor VT2. This stage converts the
A Note On IF Alignment
The December 2002, January 2003 and February 2003 issues covered
the subject of receiver alignment. As a follow-up to this, John Breden from
New Zealand advocates doing the IF alignment with the tuning gang in the
fully unmeshed position, as this obviates the possibility of tuning the IF to the
bottom of the broadcast band when the gang is closed.
This can and has happened when the IF alignment is done without using
a signal generator.
It is rare but does happen when over-enthusiastic people alter the alignment
adjustments without knowing what they are doing. Using a signal generator
ensures that the IF is aligned to the correct frequency. So if you do align the
IF without using a signal generator, just be careful you don’t fall into this trap.
December 2003 83
The Ferris
“Tranimate”
Ferris Radio (Australia) were renowned for making many innovative
devices and the “Tranimate” was one
of them. “What’s the Tranimate?”, you
may well ask. Well, the Tranimate
was a 2-transistor tuned amplifier
designed to accept a signal from a
car radio antenna and output it to a
domestic portable transistor radio.
It worked like this: a car radio
antenna was installed on the car,
complete with its coaxial cable lead.
This lead was then plugged into the
Tranimate which was screw-mounted
to the underside of the dash panel
of the car (remember, you could do
those things in 1960s cars).
The Tranimate had an input tuned
circuit and this was manually tuned
by a small tuning gang. The dial was
calibrated with some stations but being so small, only a few representative
stations were marked.
The tuned signal was first amplified
by a transistor operating in common
emitter configuration and then fed to a
second transistor wired as an emitter
follower. From there, the resulting
RF output was then fed down a thin
coaxial cable to a ferrite-cored coil
which was clipped to the transistor
radio so that it was in line with the
portable’s loopstick antenna. As a
result, the signal in the Tranimate’s
coil was induced into the loopstick
antenna and so the portable received
a clear signal.
Of course, a portable radio will
work in a car without a “signal booster” such as the Tranimate. However,
the signals tend to be weak and the
vehicle’s electrical equipment, particularly the ignition system, interferes
severely with reception. Hence the
reason for the Tranimate – it picked up
a relatively noise-free signal in a good
signal environment and amplified it
so that the noise from the vehicle’s
ignition became insignificant.
The Tranimate was powered by
a 216 battery slipped into the case
at one end. The circuitry inside the
plastic case is shielded from interference within the vehicle by metallic
plating of the inside of the case. The
tuning dial on the front is peaked up
for best reception of the station being
received.
84 Silicon Chip
The top view shows the Ferris “Tranimate”, complete with its coupling coil
and connecting coaxial cable, while immediately above is the view inside
the case. The complete unit is around the size of a packet of cigarettes.
So that was it – a simple little device that filled a small niche market
for the many people who could not
afford both a transistor portable and
a car radio at the time. I doubt that it
proved to be a winner and I obtained
mine at a clearance price. Still, it’s a
desirable item to have in a vintage
radio collection, because they are so
rare and innovative for their era.
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Fig.1: the circuit is a fairly conventional 6-transistor superhet design. Transistor
VT1 provides RF gain, while VT2 and VT3 function as the converter and IF gain
stages respectively. Diode MR2 is the detector and this feeds a direct-coupled
audio amplifier based on transistors VT4-VT6.
input signal to 455kHz and feeds it to
the IF stage.
The IF stage is based on VT3. It
amplifies the signal and because of the
high gain of this stage, it is neutralised
using capacitor C18. AGC is developed
from the signal at VT3’s collector via
C17 and diode MR1. This AGC is only
applied to VT1 in the RF stage but,
although it’s only applied to this one
stage, is still quite effective.
Detector
Diode MR2 at the output of IF transformer TR3 functions as the detector.
It feeds the detected audio signal to
the volume and tone controls, and
thence to the audio amplifier stage
which is based on transistors VT4VT6. Direct-coupled audio amplifiers
are quite common and in operation,
each stage interacts with the others.
This can make fault-finding difficult
if there is a DC fault.
Because some of the transistors are
germanium types, it is necessary to
stabilise the audio amplifier against
thermal runaway with increased temperature. This is done using thermistor
TH1 which acts to stabilise the current
drawn by the audio amplifier with
increased temperature.
VT5 is the only NPN transistor and
it has a small heatsink attached to it.
VT6, a 2N301, is mounted on the rear
heatsink and only gets slightly warm,
even after the set has been running
for some time. An auto transformer
(L7) couples the audio signal on VT6’s
collector to the loudspeaker.
Summary
This AWA car radio is a good example of germanium transistor design.
The circuit is relatively simple and
by altering just a few components, the
basic design can be adapted to either
6V or 12V DC operation. It is also quite
a good performer for a car radio from
the 1960s.
This particular set was not difficult
to restore and it showed only moderate signs of wear and tear. The pressbutton station selector still works well
and in general, it’s a receiver I would
be happy to have in my collection.
The only real criticism I have is that
the PC boards of the era are hard to
work on. The leads coming through
the board are usually bent over along
the copper tracks, making it difficult
to remove a component for testing.
It’s also necessary to be careful when
www.siliconchip.com.au
soldering to ensure that the tracks
aren’t heated excessively, otherwise
they will separate from the board or
damage one of the leads.
Finally, I find that the circuits on
these phenolic boards are difficult to
trace at times! And the draughtsman
who drew the circuit diagram omitted
the earth/chassis connection on the
SC
0V rail.
December 2003 85
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