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TRF
RADIOS
Part 2 More Reaction! |
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TRF RADIOS (Part 2) - MORE REACTION!
T.R.F. Radios Employing The "Regeneration" Technique For Extra Sensitivity And Better Selectivity
The ZN414, MK484, ZN415 and
ZN416 radios
described on the "TRF Radios Part 1" page are so called straight TRF
radios. With a
straight TRF radio the signal is passed straight through the circuit in
stages, the RF or Radio Frequency stage, the Detection or Demodulation
stage and the AF Audio Frequency amplification stage. Such
radios
use no reaction or regeneration whereby a precise amount of feedback is
used to boost the sensitivity of the circuit. A popular
design
pre-dating the ZN' circuits was the H.A.C. (Heard All Continents)
circuit. The H.A.C. uses three transistors, two of modern NPN
types for audio amplification and a rather more special FET (Field
Effect Transistor) for the RF front end. The H.A.C.
Triple-T
is described below.
My first real TRF radio was not the HAC, however, but a home made radio described in the Ladybird book "Making A transistor Radio":
My first real TRF radio was not the HAC, however, but a home made radio described in the Ladybird book "Making A transistor Radio":
|
THE
LADYBIRD THREE TRANSISTOR RADIO
"Making A Transistor Radio" by Rev George Dobbs (G3RJV) |
I
was
introduced
to
the
construction
of
TRF radios as a child with the Ladybird book 'Making A
Transistor Radio' written by Rev. G.C. Dobbs and published in
1972. The book describes how to make a reasonably simple but
very
effective radio receiver. Starting with a crystal set and
then
progressing in stages up to a powerful 3 transistor TRF radio that uses
a technique called Regeneration
(also referred to as Reaction).
This little set, when completed, used the first Radio Frequency
transistor, the Mullard OC45, three times by implementing the
regeneration method. Regeneration is positive
feedback ,
similar to the
howl-around produced when putting a
public address microphone too close to the loudspeaker. In a
radio
circuit the amount of this feedback has to be very carefully controlled
and set to just the right level, just before it begins to
howl.
In
this state the radio is at its most sensitive and is really very
selective.
Selectivity is the radio's ability to tune into one station sharply without hearing the sounds of other stations in the background. A crystal set, by contrast, tends to suffer with quite poor selectivity and is also very insensitive, requiring a really good strong signal from a large wire aerial to operate. A TRF radio, on the other hand, will often operate quite happily with just the signal picked up from an internal ferrite rod aerial, with no long wire aerial being necessary.
The Ladybird book design uses the old Mullard OC71 and OC45 germanium PNP transistors which are unfortunately no longer made, but some supplies of these germanium transistors can still be found if you are willing to search. I still have my Ladybird set that I originally built in the 1970's and it works a treat, in fact I use it to listen to the football in the garage!
If you have difficulty in obtaining the germanium PNP Mullard OC71 transistor I am informed that it can be substituted with an AF125 which is an equivalent device. I think that the AF125 or the older AF114 or AF115 or AF116 could be used too.
The OC45 transistor seems to be rather more widely available today than the OC71, but I have not yet found an equivalent for this device, although one must exist.
I am quite sure that with some research that modern silicon NPN transistors could be used in this circuit with some adjustment to component values and the reversal of the polarised components, such as the electrolytic capacitors, since with NPN transistors the battery will have to be connected with the negative side to ground, i.e. the opposite way around to the original circuit.
THE LADYBIRD REBUILT
The Ladybird book describes a novel solderless technique for construction, using a wooden 'breadboard' and brass screws and screw cups to trap the leads of the components. I have since rebuilt the radio into a smaller case and soldered the components to tag-strip for better and more reliable performance.
Selectivity is the radio's ability to tune into one station sharply without hearing the sounds of other stations in the background. A crystal set, by contrast, tends to suffer with quite poor selectivity and is also very insensitive, requiring a really good strong signal from a large wire aerial to operate. A TRF radio, on the other hand, will often operate quite happily with just the signal picked up from an internal ferrite rod aerial, with no long wire aerial being necessary.
The Ladybird book design uses the old Mullard OC71 and OC45 germanium PNP transistors which are unfortunately no longer made, but some supplies of these germanium transistors can still be found if you are willing to search. I still have my Ladybird set that I originally built in the 1970's and it works a treat, in fact I use it to listen to the football in the garage!
If you have difficulty in obtaining the germanium PNP Mullard OC71 transistor I am informed that it can be substituted with an AF125 which is an equivalent device. I think that the AF125 or the older AF114 or AF115 or AF116 could be used too.
The OC45 transistor seems to be rather more widely available today than the OC71, but I have not yet found an equivalent for this device, although one must exist.
I am quite sure that with some research that modern silicon NPN transistors could be used in this circuit with some adjustment to component values and the reversal of the polarised components, such as the electrolytic capacitors, since with NPN transistors the battery will have to be connected with the negative side to ground, i.e. the opposite way around to the original circuit.
|
MDS975
reader, Denny Lin, usefully adds these comments about semicondutor
availability:
"If you are planning to rebuild this radio, you could try some NTE transistors and diodes. Apparently the NTE102A can be used to substitute the OC45 and OC71 transistors (according to the NTE substitution web page at this web address: http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf); The characteristics of the NTE102A seem to suggest that it's a good replacement for the OC71 and not for OC45; the suggestion of AF116 yielded an equivalent transistor of NTE160, which seems to be a good replacement for the OC45 transistor (since it's a germanium oscillator). The OA81 diodes may be replaced with NTE109. Radio Shack sells an Eagle LT700 equivalent (1K primary and 8 Ohm Secondary) transformer labelled 273-1380." |
THE LADYBIRD REBUILT
The Ladybird book describes a novel solderless technique for construction, using a wooden 'breadboard' and brass screws and screw cups to trap the leads of the components. I have since rebuilt the radio into a smaller case and soldered the components to tag-strip for better and more reliable performance.
Here are some illustrations of the radio:
The Circuit Board Layout
First Stage completed - the simple crystal set radio
This
simple Crystal Set would be greatly improved with the addition of an
aerial trimmer capacitor of about 100pF connected between Screw A and
the Aerial Lead to reduce the damping on the tuned circuit (ferrite rod
coil and 0.0005uF tuning capacitor) and also a resistor and a capacitor
wired in parallel across the crystal earphone - Screw B and Screw 2.
The resistor can be of a value between between 22k and 47k Ohm. The
capacitor can be a simple disc ceramic with a value of about 0.001uF -
often marked as 102. See capacitor
and resistor charts >
Photo
showing the first two
transistor stages of the radio.
The OC45 transistor, on the left, is the radio frequency and regeneration stage. The OC71 transistor, on the right, is the first stage of audio amplification. This is followed by a second stage of amplification, which boosts the audio output enough to drive a loudspeaker - shown below below:
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|
These photographs show the
'Breadboard'
method of construction using No.6 brass wood screws and screw-cups and
a
length of 1/2 inch thick by 4 inch wide planed
softwood.
The
wires and component leads are trapped underneath the brass screw-cups
to
make a connection at each junction point. This is a good
system
for a beginner using solderless connections, but a tag-strip and
soldered joints makes for much better connections and improved
performance - so it's well worth practising a good soldering technique!
|
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|
TUNING COIL AND
COMPLETE CIRCUIT
Above: The
complete working
circuit digram. The radio performs very well indeed on the
medium
wave band, but the regeneration control has to be very carefully set
for
each station to extract best performance. Tune in a station
and
adjust the 10pF variable capacitor until the radio falls into
oscillation due to too much feedback (i.e. starts screeching), then
reduce the amount of regeneration until the screeching just
stops.
At this point the set will be at its most sensitive and its most
selective.The coil for this circuit is wound on a piece of 10mm diameter ferrite rod which is 75mm long in the illustration above, but I have used a rod that is 150mm long, which improves the amount of signal picked up and the directional characteristics. The coil is 50 turns of 36 s.w.g. enamelled copper wire close-wound, with a tap at 5 turns which is the regeneration (feedback) tap. The 0.01uF capacitor is connected to the end of the five turn winding (the regeneration amount being controlled by the 10pF variable capacitor) as can be seen in the circuit diagram below:  The 10pF variable capacitor was originally specified as a trimmer, but I have modified this and used a 15 pF variable air-spaced 'tuning' type capacitor that is mounted through the front panel to facilitate much easier adjustment of regeneration by means of a knob on the front panel, alongside the tuning and volume controls. |
|
| The
Radio Frequency Choke (R.F.C.) is about 4.7mH (milli-Henries) and any
choke near this value should be okay. The OC45 transistor amplifies the tuned radio signal once, and then again by use of feedback. The diodes are used to convert the radio frequencies to audio frequencies (detection) which the transistor then also amplifies. The two OC71 transistors add further audio amplification which will be enough to drive a loudspeaker via the Eagle LT700 transformer which converts a high impedance output from the final transistor (about 2k Ohms) to the low impedance of the 3" loudspeaker, which should be between 3 and 8 Ohms. the 10k log potentiometer is the volume control. |
The
Completed Ladybird
Radio
Above: My own
re-housed TRF
radio, with
components soldered together onto a tag strip. The left-hand
knob
is the volume control and on-off switch, the centre knob the
regeneration control and the right-hand knob is for tuning.
FOOTNOTES
Rev Gorge Dobbs (G3RJV)
In August 2005 the author of the Ladybird book "Making A Transistor Radio", Rev Gorge Dobbs (G3RJV) himself, wrote to us here at MDS975:
"Hello Mike,
Lovely to see a reference to the book. That was a long time ago! Found your site when browsing for regen receivers I am thinking of yet again looking at them in my monthly Practical Wireless column. Good to see the HAC - I remember them well!
Have fun.
My best wishes,
George, G3RJV"
Yoga Raj's Ladybird Radio
Detailed below is Yoga Raj's very neat and faithfully reproduced Ladybird Radio project. Yoga has gone to great lengths to source the now difficult to obtain components and has constructed a very impressive radio!
Dear Mike,
I stumbled upon your website on TRF radios about a year ago. At that time, it reminded me about the ladybird radio that I attempted to build while I was young but never fully completed because of incomplete parts. With your suggestions, I started collecting parts (ebay) and from all around the world to build one as good as the photos in the book. Finally,a few days ago, it was working well and much to my surprise, very well without an antenna.
I made every attempt to get the exact components where possible and stuck to the original photos on the book.
The changes made were :
1) 4.7k resistor was switched for a 1k resistor after the 1st transistor stage (gives less distortion)
2) OA81 diodes were replaced for an IN34 diode (better detection)
3) 36SWG wire for the antenna switched for a SWG 32 wire
Do have a look at the photos and your comments / questions. I live in Dunedin, New Zealand and as you see from the dial, there are many stations that I can receive without an antenna here.
Ladybird Books - Making A Transisor Radio by George Dobbs
Yoga Raj's very neat project.
Close up photograph showing the tuned circuit, detector and regeneration stage.
Note that the ferrite rod is a full 6 inches (150mm) long and not cut in half, as in
the original design. This should provide better signal pick up. The ferrite rod
is held in place by two plastic P Clips that provide a very neat and effective
method of fixing.
Close up photograph showing the audio amplification stages. Note the care taken with the
additional PVC insulation added to the component leads.
Overall view of the completed radio. Note how faithfully the leads and wires have been
formed and placed on the board between the screw cup connectors. Yoga has also connected
a small on-off switch. An alternative method might also be to use a potentiometer with
an integral switch.
Photograph showing the competed circuitry.
Photograph showing the front panel and controls of the competed radio together with a
rather impressive looking loudspeaker. As can be seen from the tuning scale on the
right hand side, an impresive number of stations can be tuned in!
Grant Searle also kindly dropped us a note and some photographs of his own faithful and extremely neatly constructed Ladybird Radio:
"Hello
there.
Thanks for a very interesting (and nostalgic) web site. I was doing a Google search for MK484 and stumbled upon your site. I was most surprised when I found your page on the Ladybird book "Making a transistor radio". I got my mum to buy this book mail-order from Ladybird when I was about 8 years old. I made the radio many years ago and still have it. It still works!! I have taken a couple of photos of it (it sits proudly on my shelf, along with the book) for you.
I kept to the layout shown in the book, but turned the tuning capacitor, volume control and speaker around so that the whole board could lie flat. I couldn't get the RFC at the time so I wound my own. As you will see, the speaker has rather faded (so has some of the wires) and the shiny brass plates on the tuning capacitor have dulled a bit but otherwise has lasted time rather well (I think I replaced a couple of the components some years ago as I raided it for some spare parts and knobs when I was desperate!). Obviously, the battery is new! If these photos are of any use to you, please feel free to use them. What impressed me was the whole thing only takes about 3mA so the battery lasts for ages.
While looking around your site I also see (to my complete astonishment!) that you also built one of my other first radios - the matchbox radio from Everyday Electronics. My magazine has, alas, parted company (and I think I know who I lent it to and lost it...) but I have the radio knocking about. I still remember the sonic bomber project from that magazine - a plane attached to a length of wood suspended from the ceiling with an electromagnet holding a ballbearing, if I remember correctly...
Anyway, it's great to see others have similar interests and experiences.
Thanks for a very interesting (and nostalgic) web site. I was doing a Google search for MK484 and stumbled upon your site. I was most surprised when I found your page on the Ladybird book "Making a transistor radio". I got my mum to buy this book mail-order from Ladybird when I was about 8 years old. I made the radio many years ago and still have it. It still works!! I have taken a couple of photos of it (it sits proudly on my shelf, along with the book) for you.
I kept to the layout shown in the book, but turned the tuning capacitor, volume control and speaker around so that the whole board could lie flat. I couldn't get the RFC at the time so I wound my own. As you will see, the speaker has rather faded (so has some of the wires) and the shiny brass plates on the tuning capacitor have dulled a bit but otherwise has lasted time rather well (I think I replaced a couple of the components some years ago as I raided it for some spare parts and knobs when I was desperate!). Obviously, the battery is new! If these photos are of any use to you, please feel free to use them. What impressed me was the whole thing only takes about 3mA so the battery lasts for ages.
While looking around your site I also see (to my complete astonishment!) that you also built one of my other first radios - the matchbox radio from Everyday Electronics. My magazine has, alas, parted company (and I think I know who I lent it to and lost it...) but I have the radio knocking about. I still remember the sonic bomber project from that magazine - a plane attached to a length of wood suspended from the ceiling with an electromagnet holding a ballbearing, if I remember correctly...
Anyway, it's great to see others have similar interests and experiences.
Grant"
Photograph of Grant's neat radio showing the detector, regeneration and
audio amplification stages.
Photograph showing how Grant included the loudspeaker
on to the base board.
Views of Grant Searle's excellent and completed "Ladybird Radio"
Here
is
an
interesting
implementation of George Dobbs' radio. Dominic Tasker
kindly sent us a description of his radio along with some photographs
of his version:
Hi Mike, Big fan of your site which inspired me to re-attempt to build the Ladybird transistor radio. I first attempted it in 1990 when I was 10 years old; I bought the book for 5p from a church jumble sale and spent 2 weeks of my summer holidayss going round radio shops and junk shops to try get the parts. That build was partially successful as it worked but I couldnt tune it in due to using the wrong tuning capacitor!
I built it recently exactly per the book, then the circuit slowly evolved (with help from your site) and my own trial and error, I have never built a radio before and I didnt really like the the wooden plank idea. I wanted to have The original design was rather deaf and under-amplified and now I pick up many more continental stations; I'm currently listening to a German jazz station!
I aimed at trying to build this from junkbox parts, some of the parts are; tuning cap pulley came from a scrap Leak Troughline tuner same as the scale pointer, the front grille and handle was from a fidelity portable that was smashed beyond repair. The diodes came from an old carousel reel to reel tape machine. I also wanted the components to look like components not specks of dust so I went all out and used 5w resistors from Maplin lucky bags and 'old school' looking electrolytic caps. The tuning system is made up of Mechano and a salvaged tuning cord. As you can see by my picture it is adjustable in the bottom left corner (rear view) on the lockable lever pulley.
The knobs were spares out of the knob box, bottom one painted black in the middle to match the top, the perspex front and back panel were out of a skip on an industrial estate. The antenna - source unknown - has been on the shelf for years and is held in with a fuse holder which came out of the reel to reel. The Celestion 3ohm speaker came out of another reel to reel. The battery is a copy of a 1970's ever ready PP9 that I made from a scan of an original, it is a very good copy.It has a modern ever ready PP9 inside it.
Yours sincerely, Dominic Tasker. Hull, East Yorkshire.
Hi Mike, Big fan of your site which inspired me to re-attempt to build the Ladybird transistor radio. I first attempted it in 1990 when I was 10 years old; I bought the book for 5p from a church jumble sale and spent 2 weeks of my summer holidayss going round radio shops and junk shops to try get the parts. That build was partially successful as it worked but I couldnt tune it in due to using the wrong tuning capacitor!
I built it recently exactly per the book, then the circuit slowly evolved (with help from your site) and my own trial and error, I have never built a radio before and I didnt really like the the wooden plank idea. I wanted to have The original design was rather deaf and under-amplified and now I pick up many more continental stations; I'm currently listening to a German jazz station!
I aimed at trying to build this from junkbox parts, some of the parts are; tuning cap pulley came from a scrap Leak Troughline tuner same as the scale pointer, the front grille and handle was from a fidelity portable that was smashed beyond repair. The diodes came from an old carousel reel to reel tape machine. I also wanted the components to look like components not specks of dust so I went all out and used 5w resistors from Maplin lucky bags and 'old school' looking electrolytic caps. The tuning system is made up of Mechano and a salvaged tuning cord. As you can see by my picture it is adjustable in the bottom left corner (rear view) on the lockable lever pulley.
The knobs were spares out of the knob box, bottom one painted black in the middle to match the top, the perspex front and back panel were out of a skip on an industrial estate. The antenna - source unknown - has been on the shelf for years and is held in with a fuse holder which came out of the reel to reel. The Celestion 3ohm speaker came out of another reel to reel. The battery is a copy of a 1970's ever ready PP9 that I made from a scan of an original, it is a very good copy.It has a modern ever ready PP9 inside it.
Yours sincerely, Dominic Tasker. Hull, East Yorkshire.
Dominic Tasker's TRF Radio with tuning scale
Rear view of Dominic Tasker's TRF Radio with tuning scale
A better view of the circuit layout
Dominic Tasker's TRF Radio
|
THE
'HEAR
ALL CONTINENTS'HAC Triple T |
HAC
stands for 'Hear All Continents', and
when this radio is used as a short wave radio reception that is
certainly possible. It is very sensitive and reasonably
selective
too. I have built one and received Japan, America, China,
Australia, Poland and Turkey, amongst many many others. This
circuit was very kindly sent to me by a Short Wave
Magazine Reader, Len from Hampshire, some years ago.
As with many such circuits of its day it used plug-in coils that were made by Denco Ltd of Clacton. The coils are no longer available, but it is perfectly possible to wind your own as I have done and obtain very good results indeed. I have provided the coil winding details below.
As with many such circuits of its day it used plug-in coils that were made by Denco Ltd of Clacton. The coils are no longer available, but it is perfectly possible to wind your own as I have done and obtain very good results indeed. I have provided the coil winding details below.
 THE TRUSTY HAC CIRCUIT DIAGRAM Note: The MPF102 F.E.T. can be substituted with the 2N3819 F.E.T. |
 THE
EXTERNAL APPEARANCE OF MY OWN HAC TRF RADIO
|
 INTERNAL
VIEW OF THE
HAC TRF RADIO
|
MULTI-BAND COIL WINDING DETAILS Coil Substitutes For The Denco (Clacton) Green Range Of Coils |
| The
old
HAC
circuit
detailed
above
is quite easy to construct, however the
design relies on the use of the DENCO (Clacton Ltd.) Green Range of
coils which are no longer available. It is quite
straightforward
to wind your own coils and the diagram on the right shows how and the
table below details the number of turns and what gauge of enamelled
copper wire to use. Take a short piece of 10mm diameter ferrite rod (about 50 to 100mm long) and make a paper sleeve to wrap around the rod (for easy repositioning of the coil assembly once in use). Over this paper sleeve wind the first coil (L1) and secure the wires 2 and 5 in place using some Sellotape. Over the top of L1 wind the second coil (L2) and secure the wires 3 and 4 in place. Finally alongside the first windings wind the third coil (L3) again securing the wires 8 and 9 in place with a little bit of Sellotape. When wiring the coil into the circuit ensure that the wires are connected in the correct place according to the numbers shown. Be especially careful not to get the wires of the regeneration coil L2 swapped over as the regeneration (reaction) effect will not occur. With a cursory glance at the schematic diagram and the drawing of the coil opposite you might expect that wire 3 from the regeneration winding (L2) would be physically next to wire 5 of the main tuning coil (L1) however wires 3 & 4 are effectively swapped over because the feedback from the Drain MPF102 field effect transistor is out of phase with its Gate and so would be out of phase with the radio signals in L1 if applied to the 'top' of the coil near the wire 5 end of L1. Since regeneration is effectively controlled positive feedback it must be applied In-Phase with the received radio signal. COIL WINDING CHART:
|
 The diagram above (top) shows
how the
coil is physically wound onto the ferrite rod former while the
circuit diagram shows the importance of the lead connection
numbering and how the coil is wired into the tuning circuit.
|
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| The number of turns for each
winding on the
coil and the gauge of enamelled copper wire used are just suggestions
that happen to work on my radios quite well. Other gauges of
wire
may be used and the number of turns adjusted until the required range
is
obtained. In any event some experimentation with the number
of
turns will always be required to obtain the required tuning range and
proper regeneration function. L3 is not too critical as it is just a coupling winding for the aerial. L1 determines the range of frequencies covered by the set and the number of turns can be increased to tune lower frequencies or decreased to tune in to higher frequencies. The most critical winding is L2 and some experimentation will almost always be required here. You may find that you can obtain reaction across most of the band but not all of it, in which case this winding will need to be adjusted by a turn or two. I found the Medium Wave coil the most difficult to get just right and had to adjust the position of the windings relative to each other to obtain satisfactory results |
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| More
About Coils |
|||||||||||||||||||||||||
In general a medium wave coil wound on a ferrite has an inductance of approximately 350 to 400 µH (microHenries) while a longwave coil will generally have an inductance of around 4 to 4.7 mH (milliHenries) |
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|
THE HAC MODEL "T" - TWIN
TRANSISTOR RADIO
.
|
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|
The
HAC company of East Grinstead, Sussex, produced radio kits
for home construction radio enthusiasts and short wave
listeners.
The three transistor circuit is described above, but Jake
Haskell
very kindly sent MDS975 photographs of his original HAC Model "T" Twin
Transistor short wave radio instruction booklet.
You can download the PDF file of the HAC Model "T" Twin Transistor Radio Kit instruction booklet HERE You will also need to have a PDF viewer, such as Adobe Reader, installed on your computer - but this is a simple matter. Visit http://www.adobe.com/ to download Adobe Reader. |
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|
THE
TWO
TRANSISTOR
WONDER
|
| MY FIRST SHORT WAVE TRF
RADIO: Here
is the circuit for my first Short Wave t.r.f. radio. As you
will
see it is very similar to the HAC described above and uses the same
type
of coils, but with just two transistors it will only power an earphone
effectively. I spent many hours with this set as a kid
listening
to short wave stations from all over the world on a crystal
earphone. Most listened to broadcasts on
this simple little radio were
Swiss Radio International, Radio Netherlands, Radio Sweden, Radio
Canada, Radio Moscow and The Voice Of Turkey - and many, many more.
I called it the TWO
TRANSISTOR
WONDER - because it was!
|
 TWO
TRANSISTOR WONDER
|
 The very old and rather battered but trusty little Two Transistor Wonder. The case is original but the knobs have been replaced with more modern ones. (Note the several holes remaining in the front panel from previous modifications). |
 The 'gubbins' inside the Two Transistor Wonder |
No
AM 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!
SSTRAN
AMT3000
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
 http://www.sstran.com/ Other AM transmitters available:
Spitfire
& Metzo Complete, high quality ready built medium wave AM
Transmitters from Vintage Components:
http://www.vcomp.co.uk/index.htm Vintage Components offer a choice of the high quality Spitfire and Metzo transmitters: SPITFIRE AM Medium Wave
Transmitter with 100 milliwatt RF output power:
 METZO AM Medium Wave Transmitter with built in compressor:  AM88 LP A basic AM transmitter kit from North County Radio. http://www.northcountryradio.com/Kitpages/am88.htm |
Worried About Soldering? Don't Be:
For some simple ideas on solderless construction techniques have a look at the Crystal Sets 2 page. 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.
< BACK
TO T.R.F. RADIOS PART 1
MORE T.R.F. RADIOS - PART 3 >
Readers Radios >
T.R.F. RADIOS - PART 4 >
Including The Medium Wave Mini >
T.R.F. RADIOS - PART 5 >
RESISTOR COLOUR CODES
AND CAPACITOR CONVERSION TABLE
MORE T.R.F. RADIOS - PART 3 >
Readers Radios >
T.R.F. RADIOS - PART 4 >
Including The Medium Wave Mini >
T.R.F. RADIOS - PART 5 >
RESISTOR COLOUR CODES
AND CAPACITOR CONVERSION TABLE
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