Nostalgic And Fascinating AM RADIO From A Single Chip TA7642!
I take a break once in a while away from my monotonous service work and involve myself in assembly. I think I can comfortably say that Radio is as fascinating today as it was when invented. I had downloaded the following circuit diagram and read other articles in the website about a wonderful single IC TA7642, AM Radio. Though I wanted to do it, it looked like the time had come at last to make one and I just went ahead with it.
https://www.petervis.com/Radios/ta7642/ta7642-am-radio-ic.html
https://circuits-diy.com/simple-am-radio-reciever-circuit-using-ta7642-ic/
cornflake_radio_TA7642.pdf (16mb.com)
A Well Behaved MK484 – or -TA7642 Radio – The RadioBoard Forums
Found a suitable ‘L’ board lying around, a balance portion of one used for some other project. When we learnt electronics, most of us would have started from a Radio.
During my ‘L’ board time in electronics, I too used a lot of ‘L’ boards that were available for assembling radios, with positions for three IFTs, RF Coils and amplifier sections, which used push-pull-type Transistors in the output. Well, I went back to my ‘Nursery’ time when I got engrossed in this work!
Picked up all components required, looked through my collections of RF coils and found one lying around and it looked as though it was waiting to be used somewhere! Picked up a gang from a discarded FM/AM board. I used only the AM section of the Gang (PVC variable capacitor with AM/FM connections on two sides). I used 150K resistor for supply to Radio IC, as mentioned in the article as I was using 9V to drive the audio amplifier IC, LM386. Drilled holes and fixed the gang first.
Then drilled holes for the Antenna Rod to be fixed. Did not fix it then. Assembled all the components one by one, taking care not to mess it up and make a mistake. Picked up a volume control with switch, 9V battery connector, a small speaker and other miscellaneous things required and completed all work within about two hours. After all these, checked and rechecked the connections before applying power.
Connected the battery and switched on from the volume control cum on/off switch. I went back to my childhood when I tuned and got stations! Well, words cannot transcribe the thrill that I got when it was working and I mentally thanked all those authors who published these articles and provided guidelines. Adjusted the coil on the ferrite rod for peak performance. I am yet to try the tweaking and making fine adjustments by providing two pots, one at the input of main power to IC and one at the output of power to RF section (A Well Behaved MK484 – or -TA7642 Radio – The RadioBoard Forums). The next day, there was no power in our area for a few hours and this Radio gave me thrilling experiences and I had a cozy rest on an old Canvas Chair listening to music. Looked like the time I chose to assemble this was good! Now and then, I picked it out of the shelf and played it and I look at like a pet and did caress sometimes! (Have I gone crazy, well, I think so!)
Of-course, mission accomplished and satisfaction got added defeating all imaginary proportions! (LOL)
This article was prepared for you by Parasuraman Subramanian from India. He is 72 years old and has more than 30 years’ experience in handling antique equipment like Valve Radio, Amps, Reel Tape Recorders and currently studying latest tech-classes conducted by Kerala State Electronics Technicians’ Association. He has done graduation in BBA degree, private diploma in Radio Engineering and retired as MD of a USA company. Presently working as Consultant to Hospital and other institutions.
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Albert van Bemmelen
June 23, 2021 at 1:04 pm
Beside the old fixing things, making new things that work is always very entertaining like you here showed!
In these times where FM radio is chosen over AM radio, now DAB radio will take its place to take over FM transmissions. Why I am planning to build some FM PLL stereo transmitters just in case they cease the old over air FM transmissions and my 'old' receivers no longer do work.
Parasuraman S
June 24, 2021 at 12:08 am
Yes, you are very correct! Advancement in technologies cause such discontinuations! But we guys, try our best to cling on to our dear most old systems which we have seen, experienced and enjoyed! Many thanks for your comments!
Stephane Schmitz
January 2, 2022 at 6:55 pm
I have 2 FM stereo FM transmitters, ready to be used in case FM disappears. My project will go further : I'll connect an internet radio module which will transmit on my old radios (or via a Bluetooth receiver).
Waleed Rishmawi
June 23, 2021 at 1:28 pm
wow, a repair technician and an inventor; very impressive my friend. I know the feeling when you put something together and the thrill you get when it works..enjoy it my friend..it is worth it. have a blessed day and thanks for sharing
Parasuraman S
June 24, 2021 at 12:08 am
Many thanks for your wonderful comments and encouragement!
William Shaw
June 24, 2021 at 1:07 am
Reminded me of the tube AM radio we built in my first electronics class in 1970!
Learned a lot but, alas, it did not work very well. Congratulations on your success!
Parasuraman S
June 24, 2021 at 9:16 pm
Ha! Ha! Good memory of first class! Nostalgic memories will recharge us for sure!
Yogesh Panchal
June 28, 2021 at 4:07 pm
Good Job!Sir,
Really thrilling experience when you make thing on your own and it works nicely.I also reminded my first project it was AM radio and while tuning it with IFT one thing i noticed that on some station we are able to pick Telephone conversation which transmitted from the local in house telephone line while your radio is near to wire of phone line it was really very thrilling moment.
Parasuraman S
June 29, 2021 at 8:24 pm
Yes, you are right! Old Radios did pick up telephone conversations and I knew a couple who eavesdropped almost all such talks and amused themselves! Unfortunately, these were also misused by miscreants those days! Many thanks for your comments!