T.R.F. RADIOS PART 1 MORE T.R.F. RADIOS - PART 3 T.R.F. RADIOS - PART 4 - including The Medium Wave Mini
T.R.F. RADIOS PART 5 TRF RADIOS - PART 6 T.R.F. RADIOS PART 7
AMATEUR RADIO BRMB Radio Birmingham
LINKS to Other Great Websites
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":
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.
THE PLANS: See The Complete Original Plans by Rev. George Dobbs G3RJV here >
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:
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.
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:
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!
My best wishes,
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!
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.
Grant Searle's Ladybird Radio
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:
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.
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.
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
Rosha and Daniel's 'Ladybird' Radio
Hi, I finally managed to make my own Ladybird Radio in Iran. I bought that book [Making A Transistor Radio] in winter 1987. My last attempt was not successful because of mistakes in the third transistor connecting and some other faults. Since I didn’t find any “OC” transistors, I used a Japanese IF Amp transistor (2SA49) instead of OC45. It was acceptable. Other transistors such ac AF117 (General Tr.) and AF126 (FM IF Tr.) didn’t work.
All of Japanese 2SB series could be used. I had some 2SB56, 2SB175 and 2SB376. .
Because I couldn’t find a radio frequency choke (r.f.c.) I used a Long Wave Coil [This would be of similar inductance]. Unfortunately my 9 volt battery was dead, so I connected a 9 volt DC power supply. My the only problem is noise.
I made some radios but I feel real satisfaction this time! Last night when I was ready to switch it on, my four year old son, Daniel, said to me: “Will you give it to me if it works this time?” ...and he owned it!
Update April 2011:
I have taken some photographs, as you see the radio works with germainium diodes OA79 and IN60 - obviously silicon diodes such as 1N4148 cannot be used.
I bought a tatty PHILIPS radio for just $2.00 with the intention of breaking it for spares, but I repaired it and replaced my 2SA49 in the Ladybird radio with a Mullard OC45 (hilips I.F. stage). But I still use Japanese one and no re-alignment was necessary.
My radio (It is better to say Daniel’s one!) has 2 trimmers and a power indicator LED. When I connect a 9 volt adapter, the third transistor (2SB376 or 2SB75) warms up - so it is better to use lower ranges such as 7.5V .Connecting a 9V battery, noise will be reduced. I admit that I didn’t spend much time making it’s box.
Thank you very much for your help and advice.
Rosha and Daniel's 'Ladybird' TRF Radio
See More Photographs of Rosha and Daniel's Radio Here >
TRF Radios Part 7
See the complete plans here >
Other 'Ladybird Radio' Resources:
A kit based on George Dobb's three transistor radio design, featured above, is available on ebay (as of December 2010 anyway).
As Dominic Tasker suggests, "...he's got lots of kits ready to go for those that done have time to bumble around for parts." See this link:
Henry's very useful related web page highlights some technical pitfalls and solutions to problems that may be encountered along the way. It also explains why substituting alternative "equivalent" transistors may not work. For example there seems to be no suitable alternative to the OC45 in the RF section in this particular circuit configuration. While the OC71 could be subsituted for an OC81, for example, but still needs a small modification to the emitter circuit. For example if substituting the first OC71 with an OC81 then it will be necessary to connect a 1k Ohm emitter resistor in parallel with a 22uF bypass capacitor to ground, rather than a direct connection to ground. This will stabilise the d.c. operating point while maintaining the audio gain.
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.
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
TRF RADIOS - PART 6
T.R.F. RADIOS PART 7
LINKS to Other Great Websites
RESISTOR COLOUR CODES
AND CAPACITOR CONVERSION TABLE
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