MDS975 logo
TRF RADIOS
Part 3
Readers' Radios
MDS975 logo
Home  |  Contact  |  Site Map  |  Links  Radio Stations & Memorabilia   |  Amateur Radio

Back to TRF RADIOS Part 1
Back to Home Page Back To Home Page
Radio, Stations & Memorabilia Crystal Sets Crystal Sets
Resistor Codes & Capacitor Conversion Tables Riding On A Wave All About Radio Waves



TRF RADIOS (Part 3) -  Readers' Radios:

Several MDS975 readers have e-mailed their transistor and integrated circuit TRF radio designs - and here they are!


AUSTIN HELLIER'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 Radio
Austin Hellier's Matchbox MK484 Radio


Austin Hellier's MK484 Radio in a Tic Tac
                          box
  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.


Update November 2013

Hello Mike,

I've been tinkering again with small MK style receivers and I'd like to send you a few pics of my latest small (and large) sets. I have learned a bit more about them and the functionality of the chip. I was able to buy 100 x TA7642 chips last year from Futurelec in Hong Kong - $40 AUD posted - quite a bargain for someone who lives at the antipodes! They still have them in stock but are now charging $50 for the same bulk buy.

First up, I've rehashed the famous "matchbox radio" and come up with a much more compact way of doing this one - it's still a bit squeezy, but it turned out a lot neater than the last one I think. Using button cells is the way to go, as you can see, there's no PC board inside the box. This one gets 10 out of 12 locals, but if I'm in the city proper I can just get 1656 right at the top end of the dial travel, and at quite good volume too!

Austin Hellier TRF Radio

Secondly, the one mounted on the 5-ply breadboard with the perspex front was a bit of a trial to build - having to align the mounting frame holes and shaft with the hole for the shaft in the perspex front, along with the back mechanism of the vernier dial AND make it look all too easy, tried my patience once or twice. Those two parts came from a local recycle centre for just $9 each - another good bargain. Vernier dials haven't been on the shop shelves here for nearly 20 years, and triple gang tuner caps can only be scavenged from old valve radios, unless you spot a reasonable bargain online. 

Austin Hellier TRF Radio

Thirdly, the cigar box one is perhaps my best performer, as it gets all 12 locals now, and tunes from below the bottom of the AM band from (around 500kHz to just over 1701), the top of the band here in OZ, and picks up the two narrow-casters (1656 and 1701) both of which can be very elusive on this simple kind of receiver. It's all in the flick of the wrist when tweaking the 10k DC feeder pot so as to cause a slight oscillation.

Austin Hellier TRF Radio

The last photograph of the radio in the grey ABS plastic box is also a good performer getting 11 out of 12 locals. Radio Brisvaani up on 1701 is very low powered and even after dark it can still be elusive too. Fitting it all in the box looks easy, but it was built in 2 stages, and stage 2 almost didn't fit at all. That's why the matrix board appears to be slightly off in its vertical alignment, but I'm still happy with the end result considering...

Austin Hellier TRF Radio

I've also come to the conclusion that better quality ferrite rods definitely lead to better sensitivity and selectivity. Low quality ferrite rods are only for junky kits, and not for the serious experimenter (I'm still stuck half way in between amateur and pro,) but I still have lots of fun with these TRF designs.

The best compact ferrite bar I can get here in Oz comes from Jaycar Electronics, and is tagged as the LF1016 in their online catalog. Longer and larger rods may work for some, but I have found them to be of poorer quality. Even those basic AM Broadcast Band coil and rod sets work better than the rods with home made coils performance wise, unless you use some good litz wire.

We were never able to get the famous ZN415 or 416 (8 pin chips) out here - ever, and I'm wondering if there's a small time supplier over there that still sells them? I'm also wondering why the ZN clone manufacturers never 'cloned' those 2 chips either? Too much trouble, or do they actually exist, but under another part number?


Thanks for posting these  sets for me. I do it so that any updated info or better techniques can be passed on, and also for the personal  satisfaction that it brings. I often use to read Gilbert Davies' books, but could never get the parts for his 2 transistor radios, as they were far too expensive back in the 1960's. Then I moved to Wollongong in late 2002, and found a recycle centre there that had been badly damaged by the floods earlier on.

Everything below a certain level on the shelves was up for grabs and at rock bottom prices too! I got several military style tuner caps, and lots of garden variety components - older in style by comparison with modern compact MKT caps and metal film resistors, but viable. I had to use the tag strip approach there sometimes due to the bulkiness of some components.

It was in Wollongong that I built up my very first version of Andy Collisons' "AM Receiver" circuit, using a triple gang tuner cap and some very heavy duty 240 volt electrical wire, stripped from a 3 core internal house wiring cable, and wound around 50 turns on a 4" diameter cardboard former. After dark, the set was so good that I could receive 1ZB and 2ZB across the Tasman Sea in NZ! That receiver had no MK or ZN components on board, as it was meant to be an el cheapo replacement for same - and it worked a treat.

I also obtained half a dozen pristine OA81 diodes - the ones I used to scavenge from the backs of old black and white TV sets, along with the IF transformers - plenty of Litz wire inside them and a ferrite rod or two that could easily be adapted to fit the AM tuning band. There were also several of each of the Mullard OC44/45 and two OC72 germanium transistors - still in their boxes - never opened or used. So I went online, found a copy of the relevant Daveys' book and actually got to build the 2 transistor TRF radio that I had dreamed of building as a 10 year old, way back in 1969, but never got the chance to. When it was properly 'tweaked' it got all the local stations, although the OC series transistors did sound a little 'mushy' in the earphone, but I was still thrilled with the results some 35 years later!

If I find out anything beneficial through my experiments, I'll pass it on. Finally, I want to thank you for past encouragement and much good info from your website - I've learned a lot about past designs from there too - keep up the good work.

Enjoy!

Austin Hellier
Brisbane Australia
November 2013


One Valve Regenerative Receivers

Hi Mike, In the last four weeks I've been experimenting with one valve regenerative AM receivers - a big step forward for a man who's dealt all his life in diodes, transistors and IC's. Here are some photographs of the two sets that I've recently completed. After weeks of reading, studying, shopping for parts and building and rebuilding, I have now have two sets that work rather well.

Using only and antenna wire (no Earth/Ground wire) I can receive all 13 local AM stations here in Brisbane as well as some DX stations. The best DX so far is the ABC local station (1548kHz) out at Emerald in the Queensland "bush". That is a distance of some 635 Kms from the Brisbane CBD Post Office (all such distances are measured from the central PO) so that's not bad for a 1T4 valve a tuned circuit, some bits and pieces and a few batteries.

One set uses the 'throttle cap' method of regeneration control, whereas the other set uses the 'pot control' method.

Austin
                            Hellier's valve regenerative radio

Austin Hellier's valve regenerative
                            radio

Austin Hellier's valve regenerative
                            radio

Working with valve sets was always a childhood dream. I remember vividly reading "Fun With Radio" by Gilbert Davey as a child back in the 1960's, but we couldn't get the Teletron or Denco/Repanco coils over here. They probably would have cost a fortune anyway - especially taking into account international postage costs. I therefore had to stick with crystal sets. For me to have the means nowadays via the Internet and Ebay, to acquire those parts at very reasonable prices, is a godsend. I'm not there yet, but when I do build one of his one or two valve receivers, with authentic parts on board, I will feel that things in the world of radio have come full circle

Thanks for the nice encouraging comments Mike, as always. It's been a rather steep learning curve these last six months, progressing from BJT designs, through to the One FET FM Regen's (Eeeek!) and now on to valves/tubes! I feel like I already have two heads - one to do the maths with, and the other to build practical layouts with - and they often end up arguing with each other...

Enjoy.

Austin Hellier
(February 2014)


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




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).











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.






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

Milan's TRF radio

Milan's TRF radio


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

and an MK484 RADIO



Circuit Diagram

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."

An MK484 RADIO


After seeing Austin Hellier’s MK484 radios, I thought that I might mention this little MK484 AM radio ‘tuner’ that I put together on the plastic lid of a  ‘zippy’ box that I had lying around a few years ago.

MK484 tuner by Felix Scerri

The circuit is pretty well ‘standard’ with a simple MK484 am radio circuit followed by a single transistor (BC549) audio preamplifier.  The alligator clip output lead is used to either take the output directly off the MK484 output or the one transistor preamplifier output, as needed.  I use mine to feed the line level input of one of my DIY ‘chip’ 15 watt stereo amplifiers using the LM1875T power op amp chip.  The amplifier drives a set of old SONAB single wide range stereo speakers that I picked up at a charity store at one time (all in mono, of course). 

I wound the antenna coil on the longest ferrite rod I could find (courtesy of ‘Jaycar’), using ‘spaced turns’ with either .25 or .315 mm enamelled copper winding wire.  I built the thing so long ago I can’t quite recall now!  The ‘power supply’ is a single 1.5 volt AA battery which lasts a long time, but disconnect it when not in use, or it will ‘go flat’ eventually.  I didn’t bother providing any power switch!

I used a variable capacitor salvaged from an ‘early’ transistor radio (I think!)  Most of the MK484 circuit is built on a small piece of veroboard, with small strips of double sided tape used to keep things in place!  It’s no work of art, but it is a sensitive and good sounding AM tuner.  The variable resistor in the battery line controls both the RF gain and volume.  Yes it’s very ‘rough and ready’, but quite effective!

73 Felix Scerri (vk4fuq) 30/11/2013.



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




No AM radio stations or transmitters in your locality or country?

http://www.vcomp.co.uk AM Medium Wave
                        Transmitter from Vintage Components

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

SSTRAN AMT3000 low power
                          AM medium wave transmitter
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:
Spitfire AM transmitter from Vintage
                              Components

METZO AM Medium Wave Transmitter with built in compressor:
Metzo AM Transmitter fromVintage
                            Components




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

< BACK TO T.R.F. RADIOS PART 2

T.R.F. RADIOS - PART 4  >

Including The Medium Wave Mini  >

TRF RADIOS - PART 5 >

TRF RADIOS - PART 6 >


LINKS to Other Great Websites >


RESISTOR COLOUR CODES
AND CAPACITOR CONVERSION TABLE




Visit my
                  Amateur Radio pages . . . .
Visit my Amateur Radio Pages >


^top of page


Home  |  Contact  |  Site Map  |  Links  Thank You  Radio Stations & Memorabilia   |  Amateur Radio

Mike Smith  -  www.MDS975.co.uk © 2005 - 2015

BRMB Radio Birmingham
ILR Birmingham
Independent Local Radio
Birmingham 96.4 FM BRMB
Les Ross - Tony Butler - George Gavin - BRMB Radio Birmingham 96.4 FM - 94.8 FM - 261 metres medium wave