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VINTAGE RADIO
By RODNEY CHAMPNESS, VK3UG
Building A Browning-Drake Replica
Many vintage radio enthusiasts would like to
have sets from the 1920s but these are now
difficult to obtain. There is an alternative,
however – build a replica that’s as close to
the original design as possible.
Collectors and restorers of old cars,
steam engines and, of course, vintage
radios, etc all like to have at least one
really special item. That item usually
takes pride of place in their collection
– it can be a real talking point and
gives the collector an opportunity to
encourage others to take up the hobby.
Wireless/radio sets from the 1920s
are often beautiful pieces of furniture
that catch the eye. Collectors like to
have at least one of these but unfortunately, they are not all that common.
As a result, replicas of that era are
often made. Often, they look almost
identical to the originals, with their
construction and performance being
similar too.
In fact, the dedication of some
constructors is so exacting that many
replicas are almost impossible to distinguish from the originals.
During 2000, the Historical Radio
Society of Australia (HRSA) decided
to promote a constructional project
for its mem
bers, the idea being to
build a replica of a popular “wireless”
from the mid-1920s. The set selected
was the Browning-Drake tuned radio
frequency (TRF) set, a fairly simple
receiver consisting of a neutralised
RF stage, a regenerative detector and
two stages of audio amplification. This
circuitry was housed in a “coffin-style”
cabinet (see photo) which was almost
universally used during the 1920s and
into the early 1930s.
Many such replicas were built, with
the parts scrounged from all sorts of
sources. As a result, they came from
many different manufacturers.
Jim’s Browning-Drake replica
One member in our local vintage
radio club is keen on building replicas from the 1920s. His name is Jim
Birtchnell and just recently, he also
decided to build a Browning-Drake
receiver.
Like all constructors of replicas, Jim
needed to scrounge as many parts as
possible for his project. These parts
either had to be identical or similar
to those used in the original receiv
ers. If he couldn’t get them, he had to
make them.
The cabinet
This view shows Jim Birtchnell’s completed Browning-Drake replica receiver.
The hinged lid allows easy access to the circuit components.
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The cabinet is one of the most
important parts in this receiver. The
original HRSA specification stated that
cabinets could be made from dressed
kiln dried timber, 7-ply board, ve
neered plywood or veneered timber.
Jim selected Kauri timber to make
his cabinet and, as can be seen from
the photographs, the cabinet is first
class. Wood-working is one of Jim’s
other hobbies, by the way.
The cabinet size is nominally
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This view inside the set clearly shows the parts arrangement and the general
wiring layout. A lot of the wiring was run using bare square-section busbar,
while the coils were wound on 76mm and 57mm-diameter PVC pipe.
530mm long, 275mm deep and 235mm
high, while the front panel is made
from black Formica. Jim decided to use
normal bronze butt-hinges to secure
the lid to the cabinet, although it’s
interesting note that most constructors
opt for a piano hinge.
A number of finishes for the cabinet
were suggested in the original HRSA
articles. These articles even included
a complete description of how to
prepare the cabinet before applying
the final finish coats. Either lacquer
or French polish was recommended
and there was sufficient detail for
constructors to do a good job using
either finish.
I must admit that the thought of
applying around 30 coats of Shellac,
to provide a beautiful French polish,
is not something I would look forward
to – especially as it’s outside my field
of expertise. Jim decided to finish his
cabinet with Mirotone lacquer, which
is an easier alternative to French polishing, and the standard of the finish
can be seen in the photos.
The various labels on the set were
made by a local screen printer and
they too look the part. In fact, the only
thing that looks a little out of place on
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the cabinet is the round power socket
that’s mounted at the rear. Although
there is a row of power supply terminals along the back, Jim decided to
also run extended leads from them to
the power socket.
This was done so that the set could
be powered from an external supply.
In fact, Jim uses this same supply
to power other replicas which have
similar requirements. In short, the
external power socket is a matter of
practicality.
Circuit details
Obtaining components of the right
vintage – or at least looking as though
they are of the right vintage – is not
an easy task when it comes to building a replica of a set that’s about 80
years old. Jim, like most others, had
difficulty sourcing some items but his
replica still looks very close to the
original set.
As shown in the photos, most
of the wiring has been done using
bare square-section busbar, some of
which has been enclosed in coloured
spaghetti sleeving. However, a small
amount of the wiring was also run in
normal plastic-covered hook-up wire
where flexibility was needed – eg, the
connections to the coils.
Generally, the wiring has been
run parallel to the sides of the case,
although there is some point-to-point
wiring. “Squared” wiring always looks
nice but may not be the most electrically efficient. However, in sets of this
vintage, lead dress and length was not
often all that important, as each stage
had relatively low gain. This meant
that the receiver was stable despite
poor layout.
Coil formers
The coil formers were made from
white PVC tubing, either three inches
(76mm) or two inches (57mm) in dia
meter. The required lengths of tubing
were first cut to length and then
spraypainted matt black to give them
an authentic look.
The windings on each of the formers
were wound on Jim’s wood lathe. In
this case, ordinary enamelled copper
wire was used but other constructors
have used double cotton-covered
copper wire, which was much more
common 80 years ago.
By the way, it’s sometimes not a good
idea to close-wind enamelled copper
wire. That’s because the distributed capacitance between the turns can be so
high that it restricts the tuning range to
June 2003 81
“tickler” coil is that its leads must be
capable of flexing many thousands of
times before breaking. This rules out
the use of single-strand wire and even
multicore hook-up wire (single-core
wire will fatigue and break after only
a few bends).
As it turns out, the most suitable
cable that’s able to withstand repeated
flexing is the “tinselled-wire” used in
old headphones. In fact, most old headphones still have their original leads
and these could be used for the job.
A practical alternative is to use a
multi-strand braid cable or any thin
cable that has many strands of very
fine wire. Jim used copper braid for
his set and this has proven to be
successful.
This close-up view shows the “regenaformer” with its rotatable “tickler” coil
for adjusting the regeneration. The RF stage and its associated neutralising
capacitor are immediately to the right of the coil.
The detector and audio stages are clearly shown in this photo. Note the two
audio transformers.
less than the complete broadcast band.
To overcome this problem, the HRSA
articles recommended that some space
be left between turns. However, despite this advice, Jim close-wound his
coils and found that the tuning range
was quite adequate.
The rotatable “tickler” coil was
more difficult to manufac
ture than
the others. This coil was wound on
the 57mm pipe and is mounted so that
it can rotate inside the 76mm former.
As shown in the photos of the “regenaformer”, the “tickler” consists of
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a split winding on the rotating coil
former. This rotating former is in turn
attached to a 0.25-inch (6.35mm) shaft
which goes through the 76mm former
via bushes scrounged from old potentiometers. One of these bushes can be
seen on the side of the “regenaformer”,
nearest the front panel.
The rotating “tickler” coil former
is clamped to the shaft to prevent any
slippage and also includes a “stop”
so that it cannot be rotated more than
about 180°.
An important requirement for the
The valves
The original Browning-Drake receivers used 201A valves and Jim
decided to stick as closely as possible
to the original design. The valves were
around $A50 each and were obtained
from the USA, as was the square section wire and the audio transformer
inserts. The HRSA article also suggested a variety of alternative valves that
could be used in a replica – eg, the 30
and the A609.
On first seeing the set, I immediately noticed the RF stage neutralising
capacitor which had come out of an
ex-service VHF transceiver. It was
ideal for the job, even if made 20 years
later than the original Browning-Drake
receivers.
Jim also had some filament rheo
stats, a high-impedance Philips
loudspeaker from the 1930s and some
old audio transformers that would
suit the set. Unfortunately though,
the audio transformers had open
circuit windings and so a couple of
1:3 step-up ratio transformers were
imported and fitted into the old cases.
The tuning capacitors were also in
Jim’s junkbox and so the set slowly
came together over a period of several
months.
Circuit details
Fig.1 shows the circuit details of
the Browning-Drake re
ceiver. It’s a
4-stage TRF design using all 201A
valves, the first stage functioning as a
neutralised triode RF amplifier.
The antenna coil (L1) is tapped
part way up the antenna coil and the
antenna circuit is tuned by C2, after
which the signal is fed to the grid of
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Fig.1: the circuit details of the Browning-Drake receiver. It’s a 4-stage TRF design using all 201A valves, the first
stage functioning as a neutralised triode RF amplifier.
V1. The resulting signal in V1’s plate
circuit is then inductively coupled
from L2 (primary) to L3 (the tuned
secondary winding). The phasing of
the primary and secondary is such
that the 5-50pF “neutraliser” capacitor feeds back a signal to the grid
that is out of phase with the tuned
antenna signal.
In practice, the “neutraliser” is
adjusted to apply enough signal of
opposite phase to cancel the grid-toplate capacitance of the valve. This
is most important if any worthwhile
signal amplification is to be achieved
in the RF stage.
V2 is a grid leak regenerative detector. The regeneration is controlled by
rotating the “tickler” coil within the
“regenaformer” until the set oscillates
(whistles on any station tuned), then
backing off for best performance. The
two terminals of the “tickler” may
need to be swapped over to obtain
regenerative performance.
The output of V2 is then applied
to a 1:3 step-up audio transformer
and is then fed to V3. V3’s output is
in turn coupled to V4 via another 1:3
step-up transformer. As can be seen
in the photos, the audio transformers
are orientated so that there is minimal
mutual inductance between them (this
is necessary even though they are in
metal cases).
The maximum gain of each audio
stage will be the normal valve gain
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This rear view of set shows the antenna earth and power supply terminals. Note
the power socket which allows an external supply to be connected.
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718 High Street Rd, Glen Waverley 3150
Ph (03) 9802 0788 FAX (03) 9802 0700
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June 2003 83
Photo Gallery: Astor “Mickey”
Model KL Mantel Radio
Radio Corporation, Melbourne, used the name “Mickey” for almost 20 years on some
their Astor mantel receivers from the late 1930s until the mid-1950s. The model KL
was introduced in 1946 and used the following valves: 6A8-G frequency changer; 6B8-G
reflexed IF amplifier/audio detector/audio amplifier/detector/AGC rectifier; 6V6-GT audio
output; and 5Y3-GT rectifier. Later versions used a 6X5-GT rectifier.
A feature of the design was the rather elaborate tone compensation circuitry connected
around a tap on the volume control and the loudspeaker voice coil. This resulted in quite
good sound from the 5-inch loudspeaker, despite the relatively small Bakelite cabinet.
The KL was available in nine different cabinet colours: walnut, green, blue, champagne,
ivory, Chinese red, mahogany, marble champagne and marble ivory. The set illustrated
is the less common (today) champagne colour. (Photo: Historical Radio Society of
Australia, Inc).
Summary
(<8) multiplied by the step-up ratio of
the audio transformer (3) – ie, about
8 x 3 =24. This means that two stages
will theoretically give an audio gain
of 24 x 24 = 576 times. This won’t be
reached in practice but a healthy 400+
gain is likely.
Alignment and operation
In reality, there is very little alignment and setting up of the set – certainly a lot less than described in the
articles I wrote in November 2002,
December 2002 and January 2003.
First, the set is connected to a
substantial aerial/antenna and earth
system and the power applied. That
done, you tune to a strong station
somewhere near the centre of the
dial, peak both tuning controls, then
adjust the regeneration control until
the set whistles. If it doesn’t whistle
and advancing the control reduces the
audio output, it is likely that the two
84 Silicon Chip
wires on the “tickler” winding have
to be reversed.
Having tuned to the strongest station and peaked the controls, it is time
to neutralise the set. However, if the
set whistles and screams when the
two tuning controls are being brought
to a peak, it is likely that the neutralisation is well out of adjustment and
the RF stage is going into self-oscilla
tion. If this is the case, you leave the
peaking just below the point where
the oscillation occurs. Winding back
V1’s filament voltage (using filament
rheostat R1) reduces the gain of this
stage and this also helps to stabilise
the set.
The next step is to remove the filament supply to V1 so that it is inoperative. However, the station that was
being received may still be just audible
in the loudspeaker but you will have
to use headphones if the stations are
not strong in your area.
Now, while listening to the station
with the RF stage disabled, you adjust
the “neutraliser” for minimum output
or, if you are lucky, no sign of the previously tuned station. The set is then
neutralised and should now be stable
under all circumstances.
It’s then just a matter of reconnecting
V1’s filament supply, after which you
should be able to tune and peak the
set for best performance. Adjusting
the two filament rheostats makes this
job just that little bit easier and they
do act as volume controls.
The RF stage and its associated
neutralising capacitor are shown in
this photo. (Note reflection of photographer on the top of the valve).
Replica sets are an interesting part
of the vintage radio hobby. In many
cases, a replica is the only way that
collector can obtain a particular 1920s
receiver.
The performance of these sets is
not something to write home about
though and they need a substantial
antenna and earth system to perform
at their best.
Finally, over the last 80 years or so,
the names of some components and
circuit configurations have changed.
There are three such names that stand
out in the Browning-Drake receiver:
(1) the “neutraliser” which is now
commonly called the neutralisation
control; (2) the “tickler” which is
now commonly called the feedback
or regeneration control; and (3) the
“regenaformer” which is now known
as a regenerative detector coil or Rein
SC
artz coil.
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