TRF Radios 3, Reader's Radios, HAC Radio, Ladybird Radio, Denco Green Coils

1: AUSTIN'S MATCHBOX & MK484 RADIOS

Austin kindly emailed from Australia:

Mike, Just a couple of pics I thought you might be interested in. The first one is my (rather scruffy) version of the matchbox radio. This box started off life as a matchbox crystal set, with a coil wound around the outer box, two short bars of ferrite rod inside and the components soldered onto a piece matrix board, which was then stuck on the top of the box.

After some tinkering and experimenting, I decided that it would better serve as an MK484 style receiver, albeit a 'bare bones' one. So after a bit of careful planning (read "stuffing components into a confined space") I came up with what you see in one of the pics. Running it off a button cell is rather limiting in terms of volume and battery longevity, but it tunes rather well, depsite its appearances.

The other set is one that I built into a Tic Tac lolly box. This took quite a bit of ingenuity, even beyond that planned for the matchbox version. However, after trying the layout sever different ways, I came upon the version you see below. When I show it to people, they often comment along the lines of : "it's an electronic equivalent of building a ship inside a bottle!"

Anyway, it's all good fun, and I hope you enjoy these pics as much as I did when I built both radios.

Austin Hellier,
Australia
Visit my website at Oz Crystal Radios

Austin Hellier's Matchbox MK484 Radio

Austin Hellier's MK484 Radio in a Tic Tac box

Visit the website: Oz Crystal Radios

The supply of MK484 chips seems to have temporarily dried up here in Oz for now, Jaycar were the main supplier, but they're not even currently listed in their online catalogue, so I've sent over to Mike Peebles (a kit supplier) for some, and some lder style diodes. It's getting more difficult to even scavenge spare parts nowadays, unless you buy old valve/transistor radios at garage sales of second hand shops.

I started off many years ago in the hobby when my father bought me an "Arrow" crystal set for my 8th birthday. This lasted a few days until I dropped it down the back stairs one afternoon. The case broke open and wires popped off the coil mount - it was broken and I was broken hearted! My father gave me a choice - either wait another month until we go to the city shopping again, and buy another one, or fix it.

I decided it would be more fun to try and fix it so off to the local library I went, and came home later that day with three books. One of them was the side of a house, I could barely carry it it was so thick and heavy - no chance of understanding it either! I forget what the second one was now, but the third one was just what I needed - a pristine copy of "Fun With Radio" by English author, Gilbert Davey. I burried myself in that book and soon the crystal set was fixed (with the aid of my dad's 60 watt 'over the shoulder' soldering iron and some very careful guidance from him on how to solder..)

So, that was that. A year later, I built my first crystal set, pinching one of mum's older breadboards from the kitchen (she didn't notice it missing for almost a week!) and winding the coil from wire I got from the next door neighbour - (he built 8 valve radios for his hobby) around the discarded cork bobbin of an old fishing reel. The diode (a Mullard OA79 black glass envelope model) was scavenged from an old balck and white TV from the local tip and the earphone was 'borrowed' from an old black phone.

It worked, although it was full of occassional pops, clicks and hums, and brought in about four or five local (Newcastle NSW) stations at reasonable volume. I used the curtain rod in my bedrom as a makeshift antenna and a ground wire was run out the front window to a metal stake in moist earth below.. Those were the days...

I had this rig for quite some months afterwards, until I could make some improvements (a proper crystal earphone, OA91 diode) and a better former for winding the now very second hand wire of the coil. Thus was my introduction to the wonderful world of electronics. Since leaving school I studied electronics full time back in 1980, then worked for the phone company for 5 years (Telecom Australia) and ended up in the business machine trade during the mid 1980's after I left the phone company. I'm now 51 and in early retirement (due to several disabillities) and once more have plenty of time to explore this fascinating hobby.

Some good chat channels to go to are www.theradioboard.com and www.midnightscience.com - there's lots of people posting there, and occasional photos of their work - very encouraging.

Austin Hellier, Australia.

2: AUGUSTIN'S RADIO

Augustin from Romania kindly e-mailed us some photographs and the details of his own 'Matchbox Radio'.

Unable to source an MK484 or ZN414 Integrated Circuit, Augustin set about constructing a two transistor radio housed in a matchbox, and has cleverly used a small polyvaricon type tuning capacitor, found in many small commercially bought pocket radios on the market, and also ingeniously 'etched' a purpose designed printed circuit board.

Hi, I'm Augustin, I live in Romania and I made my Matchbox Radio out of two transistors. I shall explain my circuit below:

THE COILS (L1 and L2):

The first coil (L1) has 75 turns of litz wire. The second coil (L2) has 7 turns. You can make the coils on a flat ferrite rod or bar. After you finish the first coil, you make the second starting from one end of the ferrite. The second coil can be made of litz or normal enamelled / insulated wire. The number of turns (7) is not too critical.

	THE VARIABLE CAPACITOR (Cv): The variable capacitor is a common type, something about 270 pf. It is not too critical. For miniaturisation it is best to use something that will fit inside the matchbox. I used a 270 pf variable capacitor from an old transistor radio.

	THE TRANSISTORS: Both of the transistors that are used in this circuit can be either BC 108 or BC 107 or BC 109. I used BC 108 transistors with a metal capsule for both. These are made in a metal capsule. The equivalents in a plastic capsule should work, but I do not guarantee it. Don't know why but those in metal capsule seem to work a little better.Anyway, I guess it's easy to find BC 108 devices. Equivalents in a plastic capsule: BC 108 - BC 172 - BC 548 - BC 238 BC 107 - BC 171 - BC 547 - BC 237 BC 109 - BC 173 - BC 549 - BC 239
	THE RESISTORS (R1, R2, R3) : R1 and R3 are 30 K Ohms R2 is 1 K Ohm THE CAPACITORS (C1 and C2 ): Both capacitors are 10 nF but the values are not too critical but do not exceed 35 nF. I stuck to using 10nF devices. The Electrolytic capacitor has a value anywhere from 2 to 33 uF. I used 33 uF.

	THE EARPHONE: I used a phone capsule with the impedance of 230 ohms. If you want to use a crystal headphone you should solder a 1K resistor in parallel with it. THE POWER SOURCE: I power the radio from a 1,5 V AAA size alkaline battery which lasts about 2 weeks non stop use. If you have any questions about my radio you can e-mail me at this address: Best wishes, Augustin. See MORE of Augustin's radios HERE

3: CHAD'S RADIO
Chad e-mailed MDS975 from Woodland Hills, USA describing the MK484 radio that he has successfully built. The circuit is slightly different to the one described above in that the headphones are 2000 Ohm magnetic types and are wired in series with the positive power supply. Chad receives three local stations at good strength plus another five at varying levels. See the circuit details (right).
Depending on the type and impedance of the magnetic headphones being used the 1k resistor marked * would need to be adjusted, but should not really be less than 470 Ohms. As in the above Matchbox Radio circuit, there is quite a good reason to use a variable preset potentiometer here as this can set the AGC at the best level and make compensation for a weakened battery. Chad's radio circuit works extremely well with 2000 Ohm magnetic headphones and even produces a result when using 32 Ohm headphones or a small loudspeaker! There is perhaps room for variation with the value of the 0.01µF (10nF) capacitor marked **, perhaps because you don't have the exact component at hand or maybe just because you like experimenting! Chad used a 62pF capacitor here. You will see that a small variation either way will effect the way the radio tunes. You could try experimenting with a 0.02µF (20nF) or a 0.005µF (5nF) capacitor here to see what the differences in gain and tuning performance are. Chad also changed the output capacitor from 0.1 uF, as shown in the diagram, to 0.04 uF. As with all radio circuits it is always worth experimenting with values, not only to see if any improvements can be made, but also just for the educational experience! For the very best results it is safe and best to stay with the value specified and keep the wiring of the circuit as neat as possible and the connecting wires short to prevent stray capacity and instability that would cause oscillations (howl) within the radio. Thank you Chad for sending in the details of your experiments and for the photos of your radio (right).
4: PETER'S RADIOS
Peter has successfully built several matchbox radios and wrote: Many thanks for your web-page, it got me interested all over again in building these radios. See photo on the right: The Brymay matchbox receives Medium Wave and uses the MK484 i.c. + BC548B transistor. The England Finest matchbox covers LongWave and uses the same circuit, both high impedance. The lower unit is the prototype with added 2N2222 for a low impedance output. All use an on-board 1.5 Volt button cell. In Devon these radios pulled in BBC Radio 4 and RTE 1 on LW. MW reception is fine too with Virgin, Talk-Sport, BBC Wales, etc. The best yet was the Radio Sweden English program. Great Fun! Good listening. Regards, Peter.

5: MILAN from Slovakia:

Hi, I´m Milan from Slovakia.

I send you the schematic for my 15 year old TRF radio for listening only one radio station. The radio was built into a plastic case of about 50x65x14 mm in dimension. I used a home made PCB. The ferrite antenna had a 75 turn winding with 10x0,05 mm wire, and a 7 turn winding with 0,3 mm wire for the connection to the BC108 transistor.

For the RF a transformer is needed with little ferrite core - see schematic and photograph. This circuit was made in a time when the power of MW transmitters was 10 times bigger than now in Slovakia.

This radio is easy and pleasant to use and is very simple to construct. It hasn´t a power switch, volume controller, or tuning control. This radio has a tuned circuit that is pre-adjusted to one favourite transmitter.

My favourite station is Slovensko One - The Slovak First Broadcasting Programme - on 1098 kHz medium wave.

Yours truly,

Milan from Slovakia

6: FELIX SCERRI :
CRYSTAL SET BASED CIRCUIT PROVIDING A HIGH QUALITY PROGRAMME SOURCE

Felix Scerri ( VK4FUQ ) kindly e-mailed us with an interesting circuit diagram, shown above, for a crystal set based receiver that will provide a high quality AM programme source.

Felix writes: "My interest in crystal sets goes back a long way and I'm particularly interested in using them as high quality AM program sources."

LINKS:

PAGES WITH ARTICLES BY RADIO EXPERT FELIX SCERRI:

High Quality AM Receivers:

http://www.crystalradio.net/scerri/index.shtml

http://www.crystalradio.net/

http://www.xtal-sets.com/

Hi Fi AM Receiver Designs:

http://sound.westhost.com/articles/am-radio.htm

OTHER ARTICLES

ESP by Rod Elliot - "Mad as Hell" & lead free solder directive:

http://sound.westhost.com/madashell.htm

ESP by Rod Elliot - CFL's (Compact Fluorescent Lamps)
http://sound.westhost.com/articles/incandescent.htm