TRF RADIOS (Part 1)
BUILD YOUR OWN
MINIATURE 'MATCHBOX' RADIO
Soldering? Don't Be:
For some simple ideas on solderless construction
techniques have a look at the Crystal Sets 2 and
the Crystal Sets 5
pages. While the ultimate miniaturisation cannot
be achieved with solderless techniques, it is still
possible to produce a working project in this way.
When constructing these small electronic projects it
will be necessary to determine the exact value of
resistors, which are colour coded, and capacitors, which
sometimes have confusing numbers on them. I have
included a table for both Resistor Colour Codes and a
Capacitor Conversion Table HERE.
very early days of wireless a TRF (Tuned Radio Frequency)
radio was the next step up from a crystal set.
It offered amplification of both the radio frequency and
the audio frequencies so that more stations could be
received more strongly and the sounds produced would be
amplified sufficiently to power a loudspeaker.
From the 1920' to the 1940's it was the glass thermionic valve
forerunner to the transistor, that was the only component
available for such amplification. A valve is quite a
large device, about the size of an eggcup and looking a
little like a small lightbulb. The valve needs its
internal working parts , the anode and cathode, to be
heated to operate (hence the term THERMionic) and so a
valve contains filaments that glow red hot. Valve
radios would consequently get quite warm and therefore use
quite a lot of power requiring several large batteries or
mains power to operate. The valve filaments needing
just a few volts to get hot, while the voltage required to
obtain a flow of electrons in the anode would need 100
volts or more.
Later radios dispensed with the TRF technology in favour
of the more sensitive and selective 'superhet' (supersonic
heterodyne) method. If the set is in good
working order the wireless listener will no doubt be
rewarded with a wonderfully rich and warm sound
quality. Many of these original valve sets had
beautifully hand-crafted wooden cabinets which would often
enclose a large loudspeaker that produced the fine sound
Old mains valve radios can be very dangerous to dismantle
and 'play around' with as they invariable have a live
metal chassis. As this chassis will be at 230 volts
mains potential the effect of a mis-positioned digit could
be fatal, so I advise against this practice. Instead
have a go at building a modern day TRF radio using the
latest solid state (i.e. silicon transistors) technology,
which operates at low power and with very low current
consumption. It was not until the introduction of
the transistor in the mid 1950's that radio sets could be
made smaller and truly portable and consume much less
power, making battery operation a practicality.
Building a TRF set today is quite straightforward as small
transistors or IC's (Integrated Circuits containing
several transistors and other components in a small sealed
device) will require only battery power in the order of
1.5 to 6 or 9 volts to operate.
As mentioned a TRF radio has its limitations and was
superceded by the Superhet
which is a principle used in all modern receivers, but the
results achieved with modern components can be
The TRF radios described
here all use transistorized circuits, though some of the
the circuit layouts are fairly similar to some early
simple valve TRF radios.
BUILD A RADIO IN
A MATCHBOX !
|The rather battered magazine cover
of Everyday Electronics
|THE MATCHBOX RECEIVER
When my dad came home one night in the 1970's with a
copy of Everyday
Electronics magazine I was fascinated by an
article describing how to home-build a radio so
small that it would fit into a matchbox. I was
a schoolboy taken with the hobby of radio and had
recently built a regenerative radio described in the
Ladybird book "Making A
Transistor Radio". This book was given
to me as a birthday present from an aunt and the
method of construction used was a simple solderless
breadboard that trapped the component leads with
number 6 brass wood screws and screw cups.
The Matchbox Receiver, on the other hand, required
careful soldering of the components into a circuit
board to achieve the small size needed to fit into a
case as small as a matchbox. I did not have a
soldering iron, I was too young.
have a soldering iron, it was not electric though
and had to be heated over a gas flame! We
spent several hours in the kitchen heating this big
iron over the gas hob and soldering the tiny
components onto the circuit board.
The matchbox receiver uses just two main components,
one that I was familiar with - a transistor (the
BC107), and a component new to me at the time, an
Integrated Circuit (I.C.) containing no less than
ten transistors inside a tiny TO-18 style can.
The I.C. used is the Ferranti ZN414 which contains a
high gain RF amplifier stage offering up to 72dB of
gain, a detector stage and a.g.c. stage.
The ZN414 has a very high input impedance of around
4meg Ohms which minimizes any loading of the tuned
circuit thereby improving selectivity, which is
important when being used in a simple TRF radio such
as is being described. The useable tuning
range available from the ZN414 is from 150kHz (Long
Wave) through Medium Wave and up to 3000kHz.
Current consumption is tiny, making it very suitable
for the matchbox radio powered by a silver-oxide
Once dad and I had soldered everything together and
assembled the parts into a matchbox I think that we
were both amazed that it worked! We received
BBC Radio Four on 285 meters, Radio Three on 464
meters, Radio One on 247 meters, Radio Birmingham on
206 meters and BRMB Radio on 261 meters.
A Matchbox Radio
particular one uses the ZN415 IC - see the
notes further down the page)
|In 1975 the idea of being able to build a
complete working radio that would fit inside an
ordinary matchbox seemed absolutely amazing.
Today it is run of the mill of course, but the
article from Everyday Electronics of Sept 1975 is
still really interesting.
As mentioned, it uses the Ferranti ZN414
integrated circuit which is no longer available,
but the direct replacement MK484 can be used with
confidence and is widely available from many
outlets including Bowood Electronics , as
are a ferrite rods, fixed capacitors, resistors,
preset pots and 500pF trimmers. You may also have
some similar and useful components in your junk
box. The circuit could still be made up
using a miniature tuning capacitor salvaged from a
discarded Chinese pocket radio. See the
alternative circuits too.
Another equivalent to the ZN414 and MK484 is, I am
informed, the TA7642 which is available from Rapid
Electronics and on ebay from Bob's TV & Radio
have now built a couple of these radios and
another one using the ZN415 I.C. which includes an
additional buffer stage of audio amplification.
So have a look at the article a little further
down the page, I'm sure that you'll find it
|DID YOU KNOW?
component sizes have been effectively reduced by
half every 18 months!
progress in design and manufacture enables
computer processor (CPU) speeds to be doubled
every 18 months.
This effect of
miniaturization is quite noticeable even when
working with the very ordinary components
involved in the construction of this matchbox
radio project, i.e. components with leads
intended for use on an ordinary circuit
When I first
built this radio in the late 1970's the
resistors and capacitors were two or three times
the size of the ones I used when re-building the
project with current components. This
helps greatly with construction inside a
process of miniaturization has progressed beyond
the 'ordinary' components that are used in
everyday 'home-brew' projects, since there is a
limit to how small such a component can be and
remain usable on standard circuit boards.
Today's powerful personal computers, laptops,
mobile 'phones and digital cameras are all made
possible by the use of very large scale
integrated circuits and miniaturized 'surface
mount' components such as resistors and
capacitors that are the size of a pin
head! These are rather more difficult to
work with for the home constructor.
showing how components have been reduced in size
as time has progressed
The top two
are 0.01µF ceramic disc capacitors, the left one
from the 1970's and the right one from 2003
two are resistors, the left one a 0.5 watt from
the 1970's and the right one from 2003
A MATCHBOX RECEIVER !
ELECTRONICS 'MATCHBOX RECEIVER' ARTICLE
Components On The Above Article:
The ZN414 I.C.
can be replaced with the current MK484 chip or the
transistor can be replaced with a BC547, a BC182 or
a ZTX300 (and other general purpose devices may work
I found that
the 680K biasing resistor could be replaced with a
470K or even a 100K without detriment.
I used a 1.55
Volt Silver Oxide battery and found that the 1K
preset potentiometer must be replaced with 10k
preset pot to give an adequate range of control over
When using a
Crystal Earphone a resistor of between 4.7k and 10k
needs to be included from the collector of the BC107
to the positive rail (after the switched jack
socket) i.e. across the earphone terminals.
This will not effect the use of 1000 ohm earphones /
Also, have a
look at the further information below for some more
SO GO AHEAD... GET
Arrangement of the ZN414 and
MK484 Integrated Circuits. The TA7642 is
apparently the same as the MK484.
Try to avoid overheating the IC when
soldering and keep the wiring of the
whole circuit as neat as is possible to
avoid unwanted oscillations that could
occur with untidy wiring.
1 : MK484
(or TA7642 or ZN414) Integrated Circuit
1 : BC107 or BC547 or ZTX300 Transistor
1 : 500pF Miniature Postage Stamp
1 : Crystal (Ceramic)
1 : 0.01 µF Ceramic (or similar)
1 : 0.1 µF Ceramic (or similar)
0.047uF (0.05µF) Ceramic (or similar)
2: 100k Ohm ¼ watt Resistor
470 Ohm ¼ watt Resistor
4.7k Ohm ¼ watt Resistor (optional)
10k Miniature Preset Potentiometer
10mm Dia Ferrite Rod 100 or 150 mm
Reel of 0.5mm (approx) Enamelled
3.5 mm Jack Socket (for earphone)
1 : AA Battery Holder
1.5 Volt AA Battery
1 : On/Off Switch (optional)
1 : Tagboard or Verostrip board
a useful source for many of these
J Birkett, The Strait, Lincoln for
surplus items such as capacitors
links to more component suppliers
|AERIAL COIL DETAILS
WAVE: 60 to 65 Turns of 0.5 mm dia enamelled
copper wire on a 10mm dia Ferrite Rod of about
35 to 40 mm long.
As above but
with 250 turns of wire.
|MY REBUILT MATCHBOX RECEIVER
matchbox receiver had got rather battered and
worn, so being as I needed to solder a new
battery into place I took the opportunity to
refurbish the radio. I used the original
Ferranti ZN414 i.c. , BC107 transistor and
500pF trimmer capacitor used for tuning.
The resistors and capacitors I replaced with
new smaller ones and I also replaced the
circuit board and the 3.5mm jack socket with a
new one as the original looked rather
corroded. A 4.7k resistor was also
included across the earphone output as I use
these radios with a crystal earpiece, as
mentioned above. I also replaced the
medium wave coil with a Long Wave coil
(purchased from Maplin Electronics) so that
the radio could tune into 198 kHz for BBC
Radio Four and also 252 kHz for RTÉ Radio
(I built another
matchbox radio, using the newer MK484 i.c, and
this covers Medium Wave. See further down this
page. A TA7642 could also be used).
|The photo above is a
little trip through England's Glory matchbox
history. The box top left is from 2004, and
the box top right is probably from the 1990's while
the box at the bottom is probably from the early
1980's. Incidentally England's Glory matches
are now made in Sweden - so shouldn't they be called
|SCRAPE OFF THE VERO-STRIPS
UNDERNEATH THE FERRITE-ROD AERIAL!
|The photograph above
shows the underside of the VeroStrip board that I
used to build the matchbox radio. Note how
three rows of copper strips have been removed using
a sharp blade. The ferrite rod aerial sits
above this area and leaving the copper in place
reduces the "Q" (the effectiveness) of the tuned
circuit very markedly.
Leaving the strips in place would result in poorer
selectivity and sensitivity of the radio and thereby
rather poor reception. I strongly recommend
removing any strips from immediately below the
ferrite rod aerial when constructing such a
radio. Also keep the aerial away from any
other metal objects that will mar the reception.
|Above photo is a close up look at
the re-built ZN414 matchbox radio
with the new Long
Wave tuning coil.
Don't despair if you cannot find some of the
components required for the Matchbox Receiver.
The resistors will be no problem, of course, and can
be 1/4 Watt, 1/2 Watt or 0.6 Watt at any
tolerance. The capacitors can be Ceramic Disc,
Resin Dipped Ceramic or Polyester and the values
stated should not be varied for best performance.
As mentioned elsewhere the ZN414 is no longer
available but the MK484 i.c. is widely and there
should be no problem obtaining one of these. The
TA7642 is another equivalent to the ZN414.
There will be no difficulty in finding a small piece
of 10mm diameter ferrite rod and some 0.5mm dia,
enamelled copper wire for the aerial.
There may be a little difficulty in finding the
500pF postage-stamp trimmer, and the 6BA brass screw
and nut to extend the tuning shaft, but some careful
searching should be rewarded with the necessary
The 500pF Trimmer For Tuning
Since components are so small these days, there will
be an opportunity to use a miniature 200pF (approx)
poly-dialectric (polyvaricon) tuning capacitor of
the type that may be salvaged from a pocket
transistor radio and that is generally more widely
available from component suppliers. This would
take up more space in the matchbox and the tuning
knob would protrude from the back face of the box
rather from one end. With careful
re-arrangement of the components and some neat
soldering there is a very good chance that
everything could be still be accommodated in a
matchbox, though I have not tried this yet.
Another alternative would be to have the matchbox
receiver permanently tuned to a favourite station.
The tuning circuit could then consist of a fixed
capacitor of perhaps 50pF or 100pF or even a
miniature trimming capacitor of similar value.
The required favourite station could then be set by
experimenting with the number of turns on the coil,
and 'fine-tuned' with the small value trimmer, if
that is what is used. This is just an idea but
then the receiver would easily fit inside a
The 3.5 jack socket has to be the open type, i.e.
not enclosed in a plastic case, so that the
switching operation can be changed from opening when
the earphone plug is inserted, to closing when the
plug is inserted. A pair of pointed nose
pliers is all that is required to bend the switching
contacts into the required position.
|ANOTHER OF MY MATCHBOX
This One Using The MK484 IC
I have recently
built another matchbox receiver, which is shown
and uses the MK484, a replacement for the
ZN414. This radio uses a ZTX300 transistor
as the audio output device which, in this case,
has a 100K biasing resistor, rather than the
680K resistor specified in the Everyday
Electronics magazine article above.
In fact a BC107, a ZTX300 or a BC547 transistor
can be used in this circuit, with a 100k biasing
resistor all with equally good results.
I strongly recommend using a crystal earphone
rather than the high impedance magnetic earphone
referred to in the article since such earphones
are almost impossible to come by. My own
Matchbox radio will drive a pair of 32 Ohm
'Walkman' type headphones to reasonable volume
when the two earpieces are wired in SERIES to
provide a 64 Ohm load, but a crystal earphone is
much MUCH louder which means that more of the
weaker stations can be heard.
recommend the use a crystal earphone, however a
4.7K Ohm resistor (up to about 10K works) needs
to be soldered across the earphone output; i.e.
between the collector of TR1 (the BC107, BC547
or ZTX300) and the positive (+ve) rail - before
the preset potentiometer and after the on/off
switch (or switched jack socket if that method
of switching is employed, as it is in my radio).
I would also
recommend the use of a 10k preset potentiometer
to set the gain, as my radio was far too loud
and rather distorted when using a new 1.55 volt
silver oxide button cell and even a 4.7K preset
potentiometer could not introduce enough
resistance into the circuit to sufficiently
reduce the gain. The 10K pot works very
well in my set.
As with all these designs don't forget to scrape
off the copper strips from the Veroboard below
the area where the ferrite rod aerial will be
mounted. Failure to remove these strips
will not prevent the radio from working, but the
performance of the tuned circuit will be marred.
Photograph showing a close-up of the inside
of my Matchbox Radio
The tiny silver oxide battery is covered in black
The skeletal jack socket has been modified so that
the contacts make a circuit when inserting
the earphone jack plug rather than breaking
the circuit as is usually the case.
This then automatically switches the radio
on when the earphone is plugged in.
POWERED MK484 MATCHBOX RADIO !
Solar Power !
I was very pleased to read about the ZN414 Matchbox
radio and its variants (MK484 & TDA7642) as I
have experimented with it before. Readers might be
interested in the fact that this little radio can
even be driven using an old solar panel salvaged
from a pocket calculator! These panels usually
provide up to 2 Volts being exposed to bright
daylight and a current of 1mA or more.
If you are worried about voltage overload simply add
a 1.5 V zener diode or a rechargeable button cell in
parallel which will cut down Voltage, thus
protecting your precious ZN414 and avoiding self
With best regards from Germany, Dietmar DH7AMQ
Thanks Dietmar -
What an excellent idea!
ALTERNATIVE MK484 (ZN414) (TA7642) CIRCUITS
Work Really Well!)
Even simpler than the 'Matchbox Radio' described
in the above 1975 Everyday Electronics article
would be to use the circuit below which omits
the amplification (BC107 transistor)
stage. The ZN414, TA7642 or MK484 is still
able to drive a simple Crystal earpiece to
reasonable volume, though obviously not as loud
as with the additional transistor
included. This approach would make it even
easier to assemble the receiver into a
matchbox. I have also constructed this set
(though not inside a matchbox) and it works
brilliantly with a simple crystal
earpiece. I decided to use a 4 inch (10cm)
long ferrite rod, which produces better signal
pick-up so that stations will be more clearly
The aerial coil consists of 60 turns of 0.56mm
diameter enamelled copper wire which gives good
coverage of the Medium Wave band even when using
a small 220 pF tuning capacitor. Battery
power is again only 1.5 volts, this time I used
a penlight AA cell which will last for a very
very long time indeed. The 10k Ohm preset
pot sets the internal gain of the MK484
integrated circuit and while not critical in
many cases careful adjustment is needed in
strong signal areas to help prevent overloading.
Keep construction of the circuit very neat with
component leads as short as is
practicable. Ideally the radio should be
built on a small piece of VeroStrip, but if you
wish to experiment with components and values
then an ordinary piece of tag-board will be
quite suitable. A 6 x 6 tag board will be
more than adequate for this circuit and I have
built these sets in this way very successfully,
but bear in mind to keep the output components
and battery away from the coil and tuning
Other component values should be adhered to to
obtain best results, the 0.1uF capacitor at Pin
1 (output) of the MK484, the 100k Ohm resistor
and the 470 Ohm resistor should not really be
changed. The 0.01µF capacitor can be
experimented with and could be between 0.01 and
0.0068 µF. The 0.05µF output de-coupling
capacitor is not too critical and the resistor
across the crystal earpiece could be 2.7K Ohm
4.7K, 6.8K perhaps up to 10K depending on
the particular earphone used. I found that
a 2.7K resistor allows my crystal earphone to
work very effectively indeed. The battery
voltage should not be changed and should be
between 1.4 and 1.6 volts. Either an
original Ferranti ZN414 IC or the later MK484 IC
can be used in these circuits, the newer
MK484 may work even better than the excellent,
but now obsolete, ZN414.
the ZN414 and
(TA7642) Integrated Circuits.
avoid overheating the IC when soldering and
keep the wiring of the whole circuit as neat
as is possible to avoid unwanted
oscillations that could occur with untidy
WAVE: 60 Turns of 0.5 mm dia enamelled copper
wire on a 10mm dia Ferrite Rod of between
100 and 150 mm long
WAVE: As above but with 250 turns of wire with
the coil ideally being shunted with a 220k
Electronics have been selling a 10mm diameter
ferrite rod with a pre-wound medium wave and
long wave coil included and this may provide
another option. Ferrite rods are also available
from Bowood Electronics.
+ See note below
1 : MK484 (or TA7642
or ZN414) Integrated Circuit
: 220pF or 500pF Tuning Capacitor
: Crystal (Ceramic) Earphone
: 0.01 µF Ceramic (or similar) Capacitor (103)
: 0.1 µF Ceramic (or similar) Capacitor (104)
1 : 0.047uF (0.05µF) Ceramic
(or similar) Capacitor (473)
1 : 100k Ohm
¼ watt Resistor
1 : 470 Ohm
¼ watt Resitor
1 : 2.7k (or
4.7k) Ohm ¼ watt Resistor
1 : 10k
1 : 10mm Dia
Ferrite Rod 100 or 150 mm long
1 : Reel of
0.5mm (approx) Enamelled Copper Wire
1 : 3.5 mm
Jack Socket (for earphone)
1 : AA Battery Holder
1 : 1.5 Volt
1 : On/Off Switch (optional)
1 : Tagboard or
is a useful
source for many of these components
May Also Try:
J Birkett, The Strait, Lincoln for surplus items
such as capacitors
Here are links to
more component suppliers
|+ Our correspondent Chas
Castagana, in the USA, had some trouble with this
circuit he writes:
I constructed this circuit as close to your
spec's as I could, ...perhaps it may be better
to feed the output into an external transistor
Chas may have been using headphones which
possibly may not work as well as a Crystal
Earphone that I had intended.
can certainly be fed into a discrete
transistor amplifier stage and will give
excellent results in this way, but even
connecting the crystal earphone between the
output and ground (as shown) I find that there
is a more than usable audio output on all
local stations. It is worth including
the circuit here due to its simplicity and
good performance. it may also be worth
experimenting with connecting the crystal
earphone between the output, via 0.05 uF
capacitor, and the positive rail (i.e. to the
positive side of the battery) and connecting
the 47k Ohm resistor across the earphone
output. Either way I don't think
constructors will be disappointed.
Thanks Chas for the input!
Single Chip MK484 Radio Constructed On A Piece
At our location I
can receive the three national stations, BBC Radio
Five Live, Talk Sport and Absolute (Virgin) Radio
from a main transmitter about 25-30 miles away
plus BBC Five Live from a main transmitter about
80 miles away on 909 kHz. Two low power
local stations (990 kHz 0.1 kW and 828 kHz 0.2 kW)
are also received at good strength from their
transmitters located 6 miles away. Before it
closed, a community station on 1350 kHz at only
0.001kW located about 4 miles away could
also be received. Additionally three other local
radio transmitters (3 to 6 kW) about 15-20 miles
away were also receivable. At night a number
of other broadcasts can be heard easily, e.g. 1440
from Luxembourg and 1512 kHz from Belgium and some
others such as 567 kHz from Eire and 675 kHz from
ADDITIONAL AUDIO AMPLIFICATION USING
THE BC548 TRANSISTOR
receiver shown below uses a BC548 transistor
as the audio output stage. It also uses
a larger ferrite rod aerial for better signal
pick-up, a standard "AA" battery cell and a
widely available miniature polyvaricon tuning
capacitor of approximately 200pF for ease of
construction. This really is a superb
completed "Cook's Matchbox Radio"
Housed in a
larger matchbox to accommodate a longer ferrite
rod aerial for improved pick-up
and a standard
"AA" battery cell together with the more orthodox
capacitor. The larger housing also makes
construction a little easier.
See the circuit
diagram for this radio below:
Circuit Diagram For The Excellent MK484 (or
TA7642 or ZN414) with the BC548 transistor
stage of amplification.
The tuning capacitor can be any standard type of
between about 200pF and 500pF and the
found in pocket radios and should be available
new from many component suppliers.
earpiece should be used, although excellent
results may be obtained with a pair of good
Ohm 'Walkman' type headphones. If these
earphones are to be used, the 32 Ohm earpieces
be wired in
SERIES so that the total load is 64 Ohms.
This can be arranged by using a stereo jack
output across the first two (small) rings of the
headphone plug and making no connection to the
part of the plug which is the common/ground
connection of the 'phones.
THE ZN415E and ZN416E
Have a look at the
circuit below which uses the ZN415 integrated
circuit, and is certainly worth using if you
happen to have one in your 'junk box'. The
ZN415 includes an additional buffer stage which
increases the output from the 30 to 60
millivolts produced by the ZN414E up to about
100 to 120 millivolts, enough to directly drive
a pair of Walkman type headphones. The two
32 ohm earpieces must be arranged so that they
are wired in series to give the necessary 64 ohm
load. The ZN415 makes assembly even easier.
The ZN416E is
similar to the ZN415E except that the output is
raised still further to about 300 to 330
Circuit digram of the Ferranti ZN415
single chip radio. This circuit can also be
used for the later higher output ZN416 and ZN416E
integrated circuits - if you can find one.
The ZN415 / ZN416 / ZN416E is, like
the ZN414, also discontinued by Ferranti, but
you may be able to find one from somewhere,
there may even be a replacement IC, but I have
not come across one.
I've read your site
on and off for a few years now and finally got
around to building a matchbox radio. I'd made one as
a child during the '70s from the PW article, with
the original Ferranti ZN414 and I'd always wanted to
make another one to have, particularly so that I
always had a mini radio to listen to the cricket on
I did cheat
slightly this time, as I ordered a kit (cheapest and
not many people sell all the parts these days) and
it came with a PCB board, my original was down on
Vero board. I will have to get some Vero board so
that I feel that I have made it 'properly'. I did
wind my own aerial coil though.
What I find
surprising, is that all the kits come with a AA
battery holder, why do you want a huge battery on a
mini radio when it will happily work off a soldered
on button battery. The other thing is they all come
with a mini on/off switch, what happened to have the
earphone socket in line with the battery, so you
switched it on by plugging the phones in.
My reason for
emailing you is the following. Rapid Electronics
appear to be selling off their AM radio kits.They're
selling them at £8.00 plus VAT (£9.60) for 5 kits.
The kits don't include the PCB, which is about £3.00
(again, that's for 5 PCBs) and the tuning knob isn't
included either (they say they've run out of them),
but they have suitable knobs for sale that are about
25p each, it's a 6mm spindle on the tuning capacitor
I thought that it
might be of interest to you or maybe the readers of
your site, if you spend £20 plus VAT it's free
delivery. It could be cheap radios for those that
might want to put it together on a vero board and
have tuning knobs lying about or rescued from old
I've just ordered
two packs (10 radio kits) with the PCBs and knobs
and I'm going to start experimenting with them. I
want a good working LW/MW/SW (individual radios),
I'll go down the matchbox route and then afterwards
see if I can buy a tidy project box that's about the
same size. Then I want to see if I can have a
combined MW/LW radio in a matchbox. I purchased a
Maplin ready wound coil / ferrite rod for MW/LW and
without the rod in the coil it picks up some MW
stations, and then LW when the coil is inserted.
I have a feeling
that my wife will probably disown me over the next
few weeks, when I bore he rigid with how the
projects are coming on.
Thanks for your
All the best, Al.
radio stations or transmitters in your
locality or country?
Has your local
medium wave broadcast station closed or been
moved to VHF/FM or Digital? Don't worry. You can
still build and experiment with crystal sets and
TRF radios by also buying or even building
a simple low power AM transmitter. So, not only
can you use your crystal sets but you can also
run your own radio station that can be heard in
and around your home - playing the music or
programmes that you want to hear!
Superb high fidelity medium
wave AM transmitter kits from SSTRAN. Versions
available for 10kHz spacing in the Americas
(AMT3000 or AMT3000-SM) and 9kHz spacing in
Europe and other areas (AMT3000-9 and
AMT3000-9SM). Superb audio quality and a great
and well designed little kit to build: http://www.sstran.com/pages/products.html
Other AM transmitters
high quality ready built medium wave AM
Transmitters from Vintage Components:
Vintage Components offer a choice of the
high quality Spitfire and Metzo transmitters:
Medium Wave Transmitter with 100 milliwatt RF
METZO AM Medium Wave Transmitter with built in
RESISTOR COLOUR CODES
CONVERSION TABLE >>>
in finding components? I have added some
ideas for component sources here.
Sources For Older
I've read your site on and off for a few years
now and finally got around to building a
matchbox radio. I'd made one as a child during
the '70s from the PW article, with the
original Ferranti ZN414 and I'd always wanted
to make another one to have, particularly so
that I always had a mini radio to listen to
the cricket on LW.
I did cheat slightly this time, as I ordered a
kit (cheapest and not many people sell all the
parts these days) and it came with a PCB
board, my original was down on Vero-board. I
will have to get some Vero-board so that I
feel that I have made it 'properly'. I did
wind my own aerial coil though.
What I find surprising, is that all the kits
come with a AA battery holder, why do you want
a huge battery on a mini radio when it will
happily work off a soldered on button battery.
The other thing is they all come with a mini
on/off switch, what happened to have the
earphone socket in line with the battery, so
you switched it on by plugging the phones in.
Anyway, my reason for emailing you is the
following. Rapid Electronics appear to be
selling off their AM radio kits.They're
selling them at £8.00 plus VAT (£9.60) for 5
kits. The kits don't include the PCB, which is
about £3.00 (again, that's for 5 PCBs) and the
tuning knob isn't included either (they say
they've run out of them), but they have
suitable knobs for sale that are about 25p
each, it's a 6mm spindle on the tuning
I thought that it might be of interest to you
or maybe the readers of your site, if you
spend £20 plus VAT it's free delivery. It
could be cheap radios for those that might
want to put it together on a vero board and
have tuning knobs lying about or rescued from
old dead radios.
I've just ordered two packs (10 radio kits)
with the PCBs and knobs and I'm going to start
experimenting with them. I want a good working
LW/MW/SW (individual radios), I'll go down the
matchbox route and then afterwards see if I
can buy a tidy project box that's about the
same size. Then I want to see if I can have a
combined MW/LW radio in a matchbox. I
purchased a Maplin ready wound coil/ferrite
rod for MW/LW and without the rod in the coil
it picks up some MW stations, and then LW when
the coil is inserted.
I have a feeling that my wife will probably
disown me over the next few weeks, when I bore
he rigid with how the projects are coming on.
Anyway, thanks for your informative website
and all the best, Al.
Hi Mike, I
was still on the trail of the matchbox
radio. At first I was cheating by using a
couple of PCBs and kits, but they weren't
quite small enough to go into a matchbox.
You'll see a MW & LW built up kit here,
not yet progressed to a project box. I tried
the PC Wireless circuit twice on copper clad
vero board, but it just wouldn't have it. So
I took a kit board apart and used the
diagram was virtually the same as PVW,
except it had a capacitor and resistor
coming off the amp transistor to the ground
and the resistor was lowered from 680k to
100k. I just wired in together and hey
presto, it worked and was almost the right
size for the box. The only thing is,
matchboxes are much smaller than they used
to be and this made it harder. I therefore
put the trimmer base down, as it was too
tall to fit the box, even side ways on.
Although this did allow me to fit a 2"
ferrite bar in the box.
The pictures below show the completed
box, open with 'gubbins' and PCB kits.
From Sean O'Connor:
Hi Mike, You might be interested in a Power
MOSFET TRF circuit I have designed and
Regards, Sean O'Connor
From Liz Costa:
Hi, MDS975 folk. I bought a
MK484 from Maplin and didn't have a circuit
for it so I entered the chip number into
Google and I was taken directly to your
site. You've given better and more detailed
info on this than Maplin have and I
certainly will be building the TRF soon. By
the way I also LOVE pussycats. Yours are
really gorgeous! Thanks for a great
Liz Costa 2E1FQN
From Dave Summer:
An interesting site. I have made valve TRF
radios since a boy in the 50’s. I heard
about 60 amateur countries on a two valve
1.4 volt set using AM. I know many hints and
kinks about making these sets work. Another
good circuit is to use a valve followed by a
transistor. If you use a 6.3 volt mains
valve, such as the 6AK5 or 6AM6, it can work
perfectly OK with 6.3V HT as well, and is
very sensitive. Of course, if you use an RF
stage the set is isolated from the aerial,
which is more steady in frequency. I find
the 1.4 valves to be poor performers and
prone to microphony.
If you want the set for short wave
reception, you can use it in oscillating
mode for CW, SSB and AM. In the case of AM,
if you use a high anode load resistor, the
circuit pulls-in slightly to the carrier.
But if you do not like this, use a low
resistor, then it does not. In practice,
these two conditions are best obtained using
a pentode with its screen acting as the
oscillator anode. Use either a high screen
dropper resistor, or a low resistance 5k
potential divider for the screen depending
if you want pull-in or not.
Modern valves are very high gain, and will
work down to a few volts of HT. It is
necessary to avoid too much regen'. A good
way is to use a trimmer as the grid
condenser, as a small capacitance of say 5
pF may be all that is needed. If you use a
small grid condenser, you are in fact
tapping the grid down the coil – it is an
impedance matching action.
Always locate the grid condenser right at
the grid, with a short lead; this prevents
As for aerial coupling, the best way is via
a small trimmer. In this way, the loading
can be adjusted. A coupling coil is not so
satisfactory and may introduce unwanted
resonances and dead spots.
A resonant aerial is not desirable as it
causes rapid changes in loading across the
band. Choose a length such as a third of a
If you want bandspread, a good method is to
tap the bandspread capacitor down the coil,
until it just gives the swing you want.
As far as hand-capacitance goes, this is a
big problem and makes the use of traditional
baseboard sets more or less useless. To
avoid hand capacitance you must have the set
in an enclosed metal box, and the phones
lead must be decoupled.
RF chokes are a bit undesirable, but the
Hartley oscillator (cathode tapped into the
coil) avoids their use. Regen can usually be
obtained using a resistor instead of a
If you use an iron cored choke in the
detector anode circuit, I believe the
circuit will suffer from threshold howl.
If you use a battery valve, or you need more
gain from a valve with very low HT, you can
take the grid leak to a positive supply,
either filament positive or HT. This
increases gain but reduces overload
Finally, you cannot use a long wave ferrite
rod in a set using a power audio IC, as the
chip ”radiates” noise in the long wave band
which will be picked up by the rod, and the
circuit will howl.
Finally, finally, although not TRF, a superb
simple superhet can be made using a crystal
controlled mixer ECH81 etc followed by an
ordinary low frequency TRF.
I hope these things are of some interest!!
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