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Vintage Radio
By RODNEY CHAMPNESS, VK3UG
Kellogg TRF receiver: home
made or manufactured?
ally impossible to distinguish between
home-made and commercial receivers
on the basis of their construction.
Certainly, in those early days, there
was no need to tip a chassis upside
down to access components. In fact,
there was no chassis – that innovation
came towards the end of the 1920s.
The Kellogg company
This simple little receiver is an excellent
example of a 3-valve TRF set from the
mid-1920s and has quite reasonable
performance. Its exact origin is somewhat
obscure, however.
I
N THE EARLY DAYS of radio/
wireless, many listeners used homemade receivers to pick up the broadcasts. Some early experimenters even
made some of the components and
only bought those parts they couldn’t
make themselves, such as valves. Of
course, this strictly wasn’t necessary
as many companies supplied a variety
of parts for radio constructors as well
as making their own radios.
The set described here is owned
by Mark and was restored by Marcus,
88 Silicon Chip
both fellow club members. All of us
are unsure as to whether it is a Kellogg
receiver made by the Kellogg company,
a home-made receiver made using Kellogg parts or a receiver built from a kit
supplied by Kellogg.
In fact, it’s often not easy to be 100%
sure as to whether receivers from the
1920s were home-made or built by a
manufacturer. All used the ubiquitous
breadboard construction style of the
era, with the parts mounted on the top
of the breadboard. As a result, it’s usu-
In Australia, the name “Kellogg” is synonymous with cornflakes. However, the company
we’re talking about here was
started by Milo Kellogg of
Chicago, who established
the Kellogg Switchboard
and Supply Company in
1897. His factory concentrated mostly on telephones
and telephone equipment and
was quite a large concern.
Milo Kellogg was a prolific
inventor and on one day in
1899 he was granted 125 patents for telephone-related
equipment. Subsequently,
when radio became the
next technological advance,
Kellogg began making components
for receivers and other equipment. I
am unsure as to whether they manufactured complete radios or not but
they certainly made some high-quality
components, as is evident from their
1923 catalog.
Kellogg remained an independent
company until 1951 when ITT bought
a controlling interest. The Kellogg
name subsequently remained until
1962 when it became ITT Kellogg
and then in 1965 it changed again to
ITT Telecommunications. There were
several other amalgamations into the
1980s and it is now a part of Cortelco.
The circuit
The Kellogg, for want of a name, is
a conventional 3-valve TRF receiver
from the mid 1920s. The antenna
tuned circuit consists of a single winding that is tapped for different-size
siliconchip.com.au
Fig.1: the circuit is a simple TRF receiver based on three UX201A triode
valves. V1 is the detector while V2 & V3 are audio amplifier stages.
antennas. It also has a tapped feedback
winding for regeneration (or reaction).
The top of the tuned section feeds
a parallel 150pF mica capacitor and
5MΩ resistor. This combination forms
a “grid leak” and is connected to the
grid of V1, a UX201A valve used as a
regenerative detector. Regeneration is
controlled by the variable capacitor
connected between its plate and the
tuned circuit.
Some readers will not be familiar
with the terms “regeneration” and
“reaction”, both of which are generally used to mean the same thing. To
explain, early radio valves had quite
low gain and were expensive, so every
endeavour was made to get the most
out of each valve. And that’s where
regeneration came in.
Regeneration is a technique whereby
the incoming radio signal is amplified
and then a portion of this amplified
signal is fed back to the input again and
re-amplified. As a result, the overall
gain of the stage is multiplied many
times. This means that the stage may
have as much gain as a more complicated (but non-regenerative) circuit
using one or two additional valves.
Each technique has its advantages
and its disadvantages. A regenerative
detector is simple, cheap to make,
sensitive and reasonably selective.
However, it can be difficult to adjust for
optimum performance, which makes it
unsuitable for non-technical users. In
addition, the audio output has higher
distortion levels than that from most
superhet receivers.
In the 1920s, however, before susiliconchip.com.au
This is the view inside the set with the top cover removed. Note the breadboard
style of construction, with all parts readily accessible from the top.
perhets became available, enthusiasts
had little option but to accept sets with
regenerative detectors if they really
wanted to listen to radio.
Following detection in V1 the audio
component of the signal appears at the
plate of the valve and is fed though a
radio frequency choke (RFC) to the primary of T1, an iron-cored 1:3 step-up
transformer. A 201 valve has a nominal
gain of around eight and by feeding its
output to this transformer, the overall
theoretical gain becomes 8 x 3 = 24.
From there, the signal is applied to
V2 where it is amplified and applied
via another audio iron-cored 1:3 step
up transformer (T2) to a third UX201A
valve (V3). The amplified audio signal
is then fed to a high-impedance horn
speaker.
Step-up transformers
Step-up transformers were necessary in the 1920s because the valves
September 2009 89
the frequency response was limited
to around 300Hz-3kHz but even that
would have had 10dB peaks and
troughs over its range. It may have
sounded terrible but that’s all that was
available in the 1920s.
Finally, the filament rheostat and the
regeneration control set the volume of
the receiver. The filament rheostat also
acts as the on-off control. This works
by having the wiper break contact with
the wire resistance element at one end
of the control’s rotation.
Restoration
These two photos show the tuning
knob before (top) and after repair
(bottom). The small central knob is
the vernier fine-tuning control.
of that era had such low gain. Their
main disadvantage was that the audio
quality was increasingly degraded as
the step-up ratio increased. However,
that didn’t matter all that much as
the detector itself had considerable
distortion, as did the horn speakers
that were used.
In fact, it’s probable that none of
the early sets had distortion figures
below about 20% or more. In addition,
Like almost all “ancient” radios, the
Kellogg TRF receiver wasn’t exactly
in pristine condition when Mark obtained it some time ago. The cabinet,
however, was still in remarkably good
condition. It was dusted out with a
brush and a vacuum cleaner and then
rubbed down with linseed oil to make
it look almost new again.
The dial had a section that had broken away but fortunately, the broken
piece was supplied with the set. The
dial, the dial shafts and the tuning
capacitors are rather unique. As usual,
a large knob turns the main part of the
tuning capacitor but now we come to
the unusual part of this tuning gang
– a separate shaft inside the main
tuning shaft controls a vernier plate
at the back.
The tuning knob for the vernier is
the small knob in the centre of the
main dial. It’s a very clever way of
doing the job but it would have required more precision during manufacture than a more conventional
tuning gang and so would have been
more expensive.
Of course, the added complexity
also makes it difficult to repair any
damage if the set is mishandled. And
that is exactly what had happened in
this case – the set had been dropped
at some stage and had landed on its
tuning knob. As a result, a section had
broken out of the knob and although
this was easy enough to repair, considerable damage had also been done
to the tuning capacitor shafts.
Suffice to say that the repairs to
the dial mechanism were not done in
five minutes. On the contrary – professional machine-shop equipment
was needed to drill and realign the
mechanism. The earthing braid that
was on the centre shaft had fatigued
and broken off too. It was replaced
but it appears as though it will be
a continuing problem that requires
routine repair.
Just why such a complex and costly
mechanism was produced for sets like
this is anyone’s guess.
Missing valves
The set was obtained with just one
valve in place and this proved to be
a Philips A415. However, although a
variety of valves could be fitted to the
set (the valve base arrangements at that
time were reasonably standardised),
it was decided to fit UX201As to the
receiver. They weren’t cheap but are
more applicable to this American-style
set than Philips valves.
Once the valves had been obtained,
it was discovered that the filament polarity had been reversed in the wiring.
This was easily corrected.
Further checking of the circuit
revealed that there was a short to the
5MΩ grid leak resistor and that audio
transformer T1 had an open-circuit
winding. The short to the resistor was
easily fixed but then it was discovered that the resistor had gone high
in value, to 14MΩ. This resistor is a
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The tuning gang is unusual in that it features an additional
single moveable plate at the back which is controlled by a
separate shaft inside the main tuning shaft. This allows the
station frequency to be precisely adjusted when tuning.
glass-mounted type and could not be
dismantled without risk of damage, so
an 8.2MΩ resistor was wired across it.
This brought the total resistance down
to the required 5MΩ.
The audio transformer problem
was fixed by replacing it with a new
one. This, along with the valves, was
obtained from overseas, as they are
difficult to find in Australia.
With the faulty parts replaced, it
was time to test various sections of
the set. To do this, an antenna, earth,
horn speaker and external power
supply were connected to the set and
the supply’s DC outputs adjusted to
the levels suggested in the valve data
sheets. This ultimately consisted of 5V
for the three filaments, -4.5V to bias the
two audio stages, +100V to the plate
circuits of the audio stages and 45V
to the detector.
The 45V HT for the detector was
derived from a variable power supply.
At just 17V HT, the detector was going into oscillation so it was in good
order and some stations could be heard
behind the whistling. However, an HT
of 45V appears to be about optimum
for this stage. Certainly, regenerative
detectors used voltages ranging from
22.5-45V for valves such as the 201A
during that era.
At full volume (ie, minimum resistance setting of the filament rheostat),
the set had a tendency to go into
supersonic oscillation. As a result, a
500pF capacitor was wired from C- to
A+ and this fixed the problem. Sets of
this era had little if any decoupling,
instead relying on the batteries to act as
siliconchip.com.au
The regeneration (or reaction) control resembles a mica
padder capacitor. Rotating the control knob varies the
distance between the plates and thus the capacitance and
the amount of regeneration.
filters and de-couplers between stages.
In addition, the sets had relatively little gain so extensive decoupling was
unnecessary.
One problem with this type of
circuit is that the audio transformers
sometimes had to have their primary or
secondary leads transposed to prevent
feedback. In other words, the terminal
marked “grid” has to be connected to
the bias line while the “bias” terminal
has to go to the grid, for stability to be
achieved.
The power leads from the set are
connected via an octal plug into a
purpose made AC power supply. This
eliminates the possibility of errors
being made when connecting the set
to power.
Alignment & performance
There are virtually no alignment
adjustments to be made in this type of
set. The tuned winding has no alternate taps to alter the tuning range and
must be accepted as it is. However, the
antenna can be tapped at two points
and a simple switch selects between
them. The tapping nearer to the earth
end of the tuned section is intended
for long antennas, while the higher tap
results in greater gain from the set to
compensate for short antennas.
The regeneration winding has one
tap so that either it or the end of the
winding can be selected to ensure
regeneration with either a 22.5V or
45V supply. The regeneration control
is rather unusual and is constructed
somewhat like a mica padder capacitor. When the plates are brought closer
Three UX201A triode valves
are used in the old Kellogg TRF
receiver.
together by rotating the control, the
amount of capacitance increases and
the regeneration increases.
Not surprisingly, the set is not parSeptember 2009 91
A close-up view of the “Little Spitfire”
decal that’s attached to the horn-load
ed loudspeaker that’s now used with
the Kellogg receiver.
with a 50mm speaker mounted above
it. As a result, it still looks original
and its performance is pretty much as
expected of a horn speaker, as it still
has the original horn baffle.
Summary
The old Kellogg 3-valve receiver was built into a wooden cabinet which
is still in good order. The on/off volume control is at bottom left, while the
reaction control is at bottom right.
ticularly sensitive but was probably
average for its time. However, it has
good selectivity and is able to discriminate between adjacent stations
quite well.
The loudspeaker
The “Little Spitfire” horn speaker
shown in the photos didn’t come
with the set but is the type of speaker
that would have been used with it.
This item was obtained separately
but unfortunately its high-impedance
winding was open circuit.
Rewinding the coil to get the speaker
going again wasn’t worth the effort.
Instead, its internals were removed
from the base and its mounting points
modified so that a small line-to-voicecoil transformer could be fitted, along
As with many very old receivers,
this unit required a lot of work to
restore it to working order. However,
it’s now a good-looking set and is an
excellent example of a mid-1920s TRF
receiver.
Its performance is fair and its ability to discriminate between stations
is good. A 10kW broadcast transmitter is located just 8km away from my
location, while a second 5kW station
is also located at a similar distance.
Together, these two station provide a
good test of a set’s selectivity.
Finally, I’d like to thank Marcus
who supplied me with the photos and
SC
information for this article.
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