JetKing DIY Radio Kits

[Subbu68]

I think I am late to the party, after all efforts I could find one from local Pune online seller.
See if this could help you -

Buy CF210SP DIY Electronic Assembly Kit for AM/FM Stereo Radio

Build your own AM/FM radio with CF210SP DIY Electronic Assembly Kit for AM/FM Stereo Radio. Buy now at the lowest price only at Robu.in

robu.in

Had seen it. It is an el cheapo Chinese.

 

[Subbu68]

@Jolly 7 @reubensm @Winter Green @omishra @Ballrick @Kannan @santaji @sdk @SRI 420 @Thirumalkumaran @mbhangui

Having awakened my love for radio tech by this thread, was hunting for a "better" radio since last two weeks or so. Also to rig up a MW tuned loop antenna.

MW has not died yet. Some stations are still there. Could receive Jodhpur, AIR Maitree, Rajkot sitting in Abu Dhabi and with my current radios (Sony ICF7600GR & ICFJ40, Sangean ATS909 and Grundig S350)

But the hunt for radios and parts for tuned loop revealed a lot to me.

First is analogue tuning is nearly dead. It is very difficult to get even a variable capacitor (for tuned loop) in the spares shops. Went to three shops in Abu Dhabi from where I got them 15 years back in plenty and they all said no one asks for it so no stock. Then thought of buying a cheap radio and salvage one from it or a AM kit and take the varicap from it.

No kits available other than that expensive Elenco. Ultimately, had to order the VCap in EBay though I went in for ALPS Japan and the kind they used in valve radios with open vanes.

Now for the radios, most radios in the market now with analogue dial are actually DSP radios inside. The varicap is gone. PLL synthesied tuning is also getting replaced by DSP. If you got one with PLL it is expensive like Tecsun PL880. No Local Ocsillators, perhaps no IFTs like this one

https://www.elektormagazine.com/magazine/elektor-201007/19338

They use Silicon Labs chips Si473X or Si483X and a pot to tune not a varicap and calibrated analog dial for cheaper versions like SONY ICF19, Panasonic RF-2400D or Tecuns, Retekess.

Ordered two DSP based radios to try out - SONY ICF19 and Panasonic RF-2400D.

And then to turn to build a DSP radio and later a DRM radio with SDR (software defined radio).

If anyone has experience with DSP radio building or DRM - SDRs please share .

 

[Subbu68]

Got my first Analog DSP radio a Sony ICF 19.

FM is superb, even FM Dxing from nearly 200kms. Listening to FM from Dubai without the antenna extended !!!

AIR Rajkot on MW came in clear and bold. Tuning is like tuning a PLL tuner with rotary encoder..a slight step is felt when change of station. Station does not fade out like in analogue..

nice solid sound

 

[reubensm]

Interesting new development:

 

[Subbu68]

Interesting new development:

That is perhaps Chinese smartness converting the work of amateurs like in the link below.

LW/MW/SW Stereo FM with RDS - DSP Radio Receiver V2.5

This is a project of Radio Receiver LW/MW/SW Stereo FM with RDS, using Arduino Nano, Si473x Radio IC and 1.8in TFT color display ST7735. By CesarSound.

www.hackster.io

Maybe I can get a DSP radio kit (analogue tuned) here and add an Audrino to control it with some mods.

 

[Jolly 7]

I have attempted to draw out my MW Transmitter circuit from memory, I hope I've got it right as the memory is from about 42 years ago

View attachment 72303
Edit: I may have used a 10k resistor instead of 2.2k in the diagram, with the 0.01uf capacitor coupled with the base of the transistor, I can't seem to remember this accurately.

@reubensm : I am happy to report that I was able to construct this circuit and generate a MW radio signal on my radios. I have used an ASZ20 germanium transistor in this circuit, although other PNP germaniums also work well e.g. a BEL AC128. However I have a problem. If I feed the transmitter with audio output e.g. from an MP3 player, it does not work and no audio is transmitted. Can you please advise how to solve this issue. Is an audio input transformer required ?

 

[Subbu68]

@reubensm : I am happy to report that I was able to construct this circuit and generate a MW radio signal on my radios. I have used an ASZ20 germanium transistor in this circuit, although other PNP germaniums also work well e.g. a BEL AC128. However I have a problem. If I feed the transmitter with audio output e.g. from an MP3 player, it does not work and no audio is transmitted. Can you please advise how to solve this issue. Is an audio input transformer required ?

Isn't ASZ20 a RF transistor? Found it is equal to AF118. AC125 is a small signal transistor like BC107? Is that why the audio is not passed on?

 

[Jolly 7]

Isn't ASZ20 a RF transistor? Found it is equal to AF118. AC125 is a small signal transistor like BC107? Is that why the audio is not passed on?

@Subbu68: Thanks for the suggestion. I think I have an AC121 which I might try. I also have other similar transistors and will try them out too.

 

[Subbu68]

@Subbu68: Thanks for the suggestion. I think I have an AC121 which I might try. I also have other similar transistors and will try them out too.

How come you have a stash of Germanium transistors?

 

[reubensm]

@reubensm : I am happy to report that I was able to construct this circuit and generate a MW radio signal on my radios. I have used an ASZ20 germanium transistor in this circuit, although other PNP germaniums also work well e.g. a BEL AC128. However I have a problem. If I feed the transmitter with audio output e.g. from an MP3 player, it does not work and no audio is transmitted. Can you please advise how to solve this issue. Is an audio input transformer required ?

let me try to recollect the sequence of events what happened to me when i built mine (please excuse the lack of memory, it is from many decades ago)

1. On first power up, i recollect it was dead, i recollect Dad coming and having a laugh, where's the ferrite rod? (i had wound my own aerial coil) without a ferrite rod I think on some paper rolled over a pen cap or something. The next day on his way back from office, a small 4 inch ferrite rod with 2 plastic holders duly arrived
2. Slipped the aerial coil over the ferrite rod, no sound, dead. Checked the aerial coil with my 6 volt bulb tester, for some reason it was open, so Dad got me a ready-made one the next day with those fiberous thin wires and I wired that in, replacing the copper wire coil. Still dead.
3. The original circuit by Sandeep Baagchi was built around AC125, i had used a spare 2N369 transistor which dad got me for making a morse code practice oscillator. Dad dug into his parts bag and gave me a AC125 and AC126 transistor pair, I replaced the 2N369 with an AC126 transistor (if i recollect correctly my wishful thinking was 126 is greater than 125 so I'll get more power from the transmitter). However, I dont remember exactly what happened, whether I overheated it while soldering or the leg broke, but anyways AC126 was damaged and I had to revert back to AC125 after an old school lecture from Dad on how to use a tweezer between the end of the leg being soldered and the transistor to protect the transistor from burning out. Great progress I was able to tune to a whoosh sound on the radio but i hadnt connected any input so did not hear anything
4. Dad then gave me a feed from one channel of his turntable, with EEI CS2000 ceramic cartridge. My initial build did not have the input coupling 10mfd cap, selector switch or volume Pot. The original design by Sandeep had the Pickup cartridge connected directly into the base of the transistor and I had this same approach. Finally, I could hear music playing on the radio but the volume was very low and distorted, Dad advised to change the 2.2k to 10k and boom, it became loud and clear
5. We then tried the output of his tape deck. Very high distortion and clipping. So he came up with the idea of the input cap (10mfd) and the volume Pot after which, i could adjust the volume and the distortion disappeared.

Note: I noticed that you have used a RF transistor, please use a AF transistor, I have tried RF transistors in later experiments with this circuit and they never worked. Many days after the AC125 success I tried BC149C with reversed battery polarity and it worked as well, but I felt AC125 sounded more soft and clean, whereas the BC149 sounded like it was overdriving the circuit

Important: Use a piece of wire as an aerial but ensure that the wire is not grounded or you dont touch it. I recollect that if I touched the collector of the transistor, the aerial coil, the gang capacitor active pins the 0.005uf capacitor or the aerial, transmission would stop and would resume after I removed my fingers from the vicinity.

Useful: As i was a little kid, dad would not let me play with electricity, so i had an old school battery box which held upto 6 x 1.5 volts torch batteries (9 volts), by slipping the connecting jumper plate one step forward, one could use 4 x 1.5 volts batteries and get 6 volts. This was my power source. Years later i had tried this circuit with my battery eliminator (I had a switchable one with 9v and 6v) and it did not work well due to some electric hum and inteference. Batteries always gave the best results.

Here is the original schematic without the input additions and with the 10k mod. I later added those input extras in order to drive the transmitter with the line output of a cassette deck.


I know all this may sound very ancient and dumb in the modern context but for little ordinary kids like us in those gloroius old days without google or even reference books, these little gadgets were stunning achievements and allowed us to earn the tag of "brilliant child", "future scientist" etc in our times. Thanks for helping me to re-live those great memories!

Also I found this other circuit online which is similar to the one from Sandeep Baagchi, which I constructed. This one has a condenser microphone preamp and also uses BC109C transistors instead. Probably the 1k and condenser microphone can be elimanated and a normal line input feed, can be used instead.

 

[Jolly 7]

How come you have a stash of Germanium transistors?

Hi. I've been collecting various components and other weird and wonderful gadgets over many years from many different places. These are indispensable for various vintage projects such as this transmitter one.

 

[Subbu68]

Hi. I've been collecting various components and other weird and wonderful gadgets over many years from many different places. These are indispensable for various vintage projects such as this transmitter one.

Have no space and also being an expat hoarding is prohibited (risk of moving back to India ,). So had to leave all my collection at my father's house.. no idea if he kept it or threw them.

 

[Jolly 7]

let me try to recollect the sequence of events what happened to me when i built mine (please excuse the lack of memory, it is from many decades ago)

1. On first power up, i recollect it was dead, i recollect Dad coming and having a laugh, where's the ferrite rod? (i had wound my own aerial coil) without a ferrite rod I think on some paper rolled over a pen cap or something. The next day on his way back from office, a small 4 inch ferrite rod with 2 plastic holders duly arrived
2. Slipped the aerial coil over the ferrite rod, no sound, dead. Checked the aerial coil with my 6 volt bulb tester, for some reason it was open, so Dad got me a ready-made one the next day with those fiberous thin wires and I wired that in, replacing the copper wire coil. Still dead.
3. The original circuit by Sandeep Baagchi was built around AC125, i had used a spare 2N369 transistor which dad got me for making a morse code practice oscillator. Dad dug into his parts bag and gave me a AC125 and AC126 transistor pair, I replaced the 2N369 with an AC126 transistor (if i recollect correctly my wishful thinking was 126 is greater than 125 so I'll get more power from the transmitter). However, I dont remember exactly what happened, whether I overheated it while soldering or the leg broke, but anyways AC126 was damaged and I had to revert back to AC125 after an old school lecture from Dad on how to use a tweezer between the end of the leg being soldered and the transistor to protect the transistor from burning out. Great progress I was able to tune to a whoosh sound on the radio but i hadnt connected any input so did not hear anything
4. Dad then gave me a feed from one channel of his turntable, with EEI CS2000 ceramic cartridge. My initial build did not have the input coupling 10mfd cap, selector switch or volume Pot. The original design by Sandeep had the Pickup cartridge connected directly into the base of the transistor and I had this same approach. Finally, I could hear music playing on the radio but the volume was very low and distorted, Dad advised to change the 2.2k to 10k and boom, it became loud and clear
5. We then tried the output of his tape deck. Very high distortion and clipping. So he came up with the idea of the input cap (10mfd) and the volume Pot after which, i could adjust the volume and the distortion disappeared.

Note: I noticed that you have used a RF transistor, please use a AF transistor, I have tried RF transistors in later experiments with this circuit and they never worked. Many days after the AC125 success I tried BC149C with reversed battery polarity and it worked as well, but I felt AC125 sounded more soft and clean, whereas the BC149 sounded like it was overdriving the circuit

Important: Use a piece of wire as an aerial but ensure that the wire is not grounded or you dont touch it. I recollect that if I touched the collector of the transistor, the aerial coil, the gang capacitor active pins the 0.005uf capacitor or the aerial, transmission would stop and would resume after I removed my fingers from the vicinity.

Useful: As i was a little kid, dad would not let me play with electricity, so i had an old school battery box which held upto 6 x 1.5 volts torch batteries (9 volts), by slipping the connecting jumper plate one step forward, one could use 4 x 1.5 volts batteries and get 6 volts. This was my power source. Years later i had tried this circuit with my battery eliminator (I had a switchable one with 9v and 6v) and it did not work well due to some electric hum and inteference. Batteries always gave the best results.

Here is the original schematic without the input additions and with the 10k mod. I later added those input extras in order to drive the transmitter with the line output of a cassette deck.
View attachment 72605

I know all this may sound very ancient and dumb in the modern context but for little ordinary kids like us in those gloroius old days without google or even reference books, these little gadgets were stunning achievements and allowed us to earn the tag of "brilliant child", "future scientist" etc in our times. Thanks for helping me to re-live those great memories!

Also I found this other circuit online which is similar to the one from Sandeep Baagchi, which I constructed. This one has a condenser microphone preamp and also uses BC109C transistors instead. Probably the 1k and condenser microphone can be elimanated and a normal line input feed, can be used instead.

View attachment 72607

Thank you for sharing your treasured memories and further circuit details. I think that, in the first version of the circuit I built, connecting an external audio source was stopping the transistor from oscillating altogether. I am not sure why that is. However, I was fortunate to have found a small matching transformer in my parts box that allowed me to overcome this problem. With the transformer now in place, I can now hear the audio input from the transmitter on my AM radio very clearly. In relation to the type of transistor I have used I found that a Mullard OC45 works best for me. I tried an AC121, an AC125, a 2SB77 and an AC128, but the OC45 seems to be giving me the clearest signal. Some of the other transistors produced 'whines'.There are harmonics being generated with all of these transistors but maybe that can be sorted. I didn't need to connect an antenna to be able to receive the signal on my radio within a couple of inches of this circuit.

 

[reubensm]

Thank you for sharing your treasured memories and further circuit details. I think that, in the first version of the circuit I built, connecting an external audio source was stopping the transistor from oscillating altogether. I am not sure why that is. However, I was fortunate to have found a small matching transformer in my parts box that allowed me to overcome this problem. With the transformer now in place, I can now hear the audio input from the transmitter on my AM radio very clearly. In relation to the type of transistor I have used I found that a Mullard OC45 works best for me. I tried an AC121, an AC125, a 2SB77 and an AC128, but the OC45 seems to be giving me the clearest signal. Some of the other transistors produced 'whines'.There are harmonics being generated with all of these transistors but maybe that can be sorted. I didn't need to connect an antenna to be able to receive the signal on my radio within a couple of inches of this circuit.

interesting mod, kindly share some details regarding the transformer and how you have connected it in the circuit.

 

[Jolly 7]

interesting mod, kindly share some details regarding the transformer and how you have connected it in the circuit.

Here is how I connected the transformer. I am not sure how critical the values of the primary and secondary coil resistances are in this circuit. It could be that all that is required is a reasonable amount of electrical isolation and adequate electromagnetic coupling between the audio input and the transmitter circuit.
P.S. I've borrowed your circuit diagram and pen. Hope you don't mind.

 

[Subbu68]

let me try to recollect the sequence of events what happened to me when i built mine (please excuse the lack of memory, it is from many decades ago)

1. On first power up, i recollect it was dead, i recollect Dad coming and having a laugh, where's the ferrite rod? (i had wound my own aerial coil) without a ferrite rod I think on some paper rolled over a pen cap or something. The next day on his way back from office, a small 4 inch ferrite rod with 2 plastic holders duly arrived
2. Slipped the aerial coil over the ferrite rod, no sound, dead. Checked the aerial coil with my 6 volt bulb tester, for some reason it was open, so Dad got me a ready-made one the next day with those fiberous thin wires and I wired that in, replacing the copper wire coil. Still dead.
3. The original circuit by Sandeep Baagchi was built around AC125, i had used a spare 2N369 transistor which dad got me for making a morse code practice oscillator. Dad dug into his parts bag and gave me a AC125 and AC126 transistor pair, I replaced the 2N369 with an AC126 transistor (if i recollect correctly my wishful thinking was 126 is greater than 125 so I'll get more power from the transmitter). However, I dont remember exactly what happened, whether I overheated it while soldering or the leg broke, but anyways AC126 was damaged and I had to revert back to AC125 after an old school lecture from Dad on how to use a tweezer between the end of the leg being soldered and the transistor to protect the transistor from burning out. Great progress I was able to tune to a whoosh sound on the radio but i hadnt connected any input so did not hear anything
4. Dad then gave me a feed from one channel of his turntable, with EEI CS2000 ceramic cartridge. My initial build did not have the input coupling 10mfd cap, selector switch or volume Pot. The original design by Sandeep had the Pickup cartridge connected directly into the base of the transistor and I had this same approach. Finally, I could hear music playing on the radio but the volume was very low and distorted, Dad advised to change the 2.2k to 10k and boom, it became loud and clear
5. We then tried the output of his tape deck. Very high distortion and clipping. So he came up with the idea of the input cap (10mfd) and the volume Pot after which, i could adjust the volume and the distortion disappeared.

Note: I noticed that you have used a RF transistor, please use a AF transistor, I have tried RF transistors in later experiments with this circuit and they never worked. Many days after the AC125 success I tried BC149C with reversed battery polarity and it worked as well, but I felt AC125 sounded more soft and clean, whereas the BC149 sounded like it was overdriving the circuit

Important: Use a piece of wire as an aerial but ensure that the wire is not grounded or you dont touch it. I recollect that if I touched the collector of the transistor, the aerial coil, the gang capacitor active pins the 0.005uf capacitor or the aerial, transmission would stop and would resume after I removed my fingers from the vicinity.

Useful: As i was a little kid, dad would not let me play with electricity, so i had an old school battery box which held upto 6 x 1.5 volts torch batteries (9 volts), by slipping the connecting jumper plate one step forward, one could use 4 x 1.5 volts batteries and get 6 volts. This was my power source. Years later i had tried this circuit with my battery eliminator (I had a switchable one with 9v and 6v) and it did not work well due to some electric hum and inteference. Batteries always gave the best results.

Here is the original schematic without the input additions and with the 10k mod. I later added those input extras in order to drive the transmitter with the line output of a cassette deck.
View attachment 72605

I know all this may sound very ancient and dumb in the modern context but for little ordinary kids like us in those gloroius old days without google or even reference books, these little gadgets were stunning achievements and allowed us to earn the tag of "brilliant child", "future scientist" etc in our times. Thanks for helping me to re-live those great memories!

Also I found this other circuit online which is similar to the one from Sandeep Baagchi, which I constructed. This one has a condenser microphone preamp and also uses BC109C transistors instead. Probably the 1k and condenser microphone can be elimanated and a normal line input feed, can be used instead.

View attachment 72607

Took me back to my childhood exploits. I used to get some monetary support at times. Other than that my dad took me to the shops and introduced to an "uncle" who worked in Cochin Shipyard and another who repaired stuff in his shop. Shipyard uncle gave me some stuff that had a lot of power transistors..maybe some are still in dad's place.

Had a friend Thomas with whom I used to do those experiments..EFY, Elektor were always welcome. I have a treasure for you and @Jolly 7 . I will send link to you to download .

Got these now from Thailand. Alps variable caps.

 

[reubensm]

Here is how I connected the transformer. I am not sure how critical the values of the primary and secondary coil resistances are in this circuit. It could be that all that is required is a reasonable amount of electrical isolation and adequate electromagnetic coupling between the audio input and the transmitter circuit.
P.S. I've borrowed your circuit diagram and pen. Hope you don't mind.

this is great, OC45 a RF transistor used in the detector stage of old 'all-transistor' european radios, right? So that should be similar to AF117? I think OC45 had only 3 connecting legs while AF117 had 4 (the one additional was wired to the metal body of the transistor for grounding i think)

 

[Subbu68]

this is great, OC45 a RF transistor used in the detector stage of old 'all-transistor' european radios, right? So that should be similar to AF117? I think OC45 had only 3 connecting legs while AF117 had 4 (the one additional was wired to the metal body of the transistor for grounding i think)

Bringing back the memories

Now this is the link I was telling . I used to read it in Manorama Book Stall near my house and drool over getting it.

https://worldradiohistory.com/BOOKSHELF-ARH/Author-Groups/G.C.Dobbs/Making-a-Transistor-Radio-Dobbs.pdf

Another link with a clearer copy. There is an option to download too

Making a Transistor Radio : G. C. Dobbs : Free Download, Borrow, and Streaming : Internet Archive

A Ladybird book, the only one in the 724 series, detailing how to make a transistor radio. Illustrated by B. H. Robinson, with ISBN 0721403247.

archive.org

Used this to introduce radio to my daughter (neck deep in iPad, iPhone, iTunes and her MBBS) a few months back.

Did not know until later that my dad had a treasure trove with him. I remember him sitting and teaching me radio basics when in 6th Std. (1979) from a book named Basic Radio Course.

Not sure if this is that book https://worldradiohistory.com/BOOKS...back/Gernsback-44-Basic-Radio-Course-Frye.pdf

I don't remember the author name.

and he had these I think

https://worldradiohistory.com/BOOKSHELF-ARH/Rider-Books/Rider-Basic-Radio-Vol-1-Tepper.pdf

Alas!! in the melee of life he did not update himself from tubes and some bit of transistors.

 

[reubensm]

The common thread was always dad introducing the kids to electronics. Growing up in a typical Indian 1970s/80s family, dad wanted me to become an engineer (like him), mom wanted me to become a doctor, but when i completed my PDC (PCB+M) and after the entrance success - being allocated to Mech-Engg and BVSc & AH from both streams, I decided to take up neither and started my accountancy journey. Dad retired in 1995 and enjoyed the rest of his days with shortwave listening (died 2009). From 1994 onwards, I started swapping my DIY rigs with all branded stuff from the shop window (and later on from my travels abroad), when the earnings started, and gave up DIY completely (a young Indan corporate worker ends up in a performance-based rat race and has little time for anything), until when one of our FMs approached me to build a ceramic phonostage and I also joined the CNC phonostage adventures from our forum.

 

[Subbu68]

, I decided to take up neither and started my accountancy journey.

that is fantastic you remember the electronics even now.

From 1994 onwards, I started swapping my DIY rigs with all branded stuff from the shop window (and later on from my travels abroad), when the earnings started, and gave up DIY completely (a young Indan corporate worker ends up in a performance-based rat race and has little time for anything), until when one of our FMs approached me to build a ceramic phonostage and I also joined the CNC phonostage adventures from our forum.

That is the saddest thing when we think branded stuff are superior and of course the career and associated rat race. In my case it was the uncertainty working in project sites that held me back ... until 2016 when the urge to replace my amp came in and started the DIY again.

Now this thread and into radios again.