New kits arrived - not vintage per se but vintage

[Subbu68]

Not vintage but vintage tech. 3 kits arrived from Amazon.

AM 2 IC kit - though IC it is a vintage tech circuit - IC is 7642 and radio is Tuned RF radio. Second IC is the audio amplifier part.

FM Auto scan radio

Radios are vintage when all speak of Spotify or Tidal . Will try to hook it up with my pre-amp / ACA amp set up.


Classic Superhet transistor based AM / FM kit with LM386 amp section



Back to where it all started - radio assembly and get the basics right. Never learnt anything in deep in radios as I got electrocuted with power systems.

 

[Jolly 7]

The TA7642 used in the Elenco MW radio kit is one of my favourite ICs to experiment with. I have made a couple of radios with it and generally the sensitivity is very good. I have also experimented with the MK484, a predecessor IC, also based on TRF.

 

[Subbu68]

The TA7642 used in the Elenco MW radio kit is one of my favourite ICs to experiment with. I have made a couple of radios with it and generally the sensitivity is very good. I have also experimented with the MK484, a predecessor IC, also based on TRF.

Hi Jolly,

I made the TRF radio and is sensitive but the local blowtorches torch distant stations. I was able to listen to AIR. Rajkot on 810kHz sitting in Abu Dhabi. I have posted it under AM/FM Tuners thread.

There is an overlapping station on whichever radio I try but there is also a local one in the background nearly all over the band. Were you able to make any of your TRFs selective? Would using a coupling coil instead of feeding in the IC from the tank circuit itself improve it?

 

[Jolly 7]

Hi Jolly,

I made the TRF radio and is sensitive but the local blowtorches torch distant stations. I was able to listen to AIR. Rajkot on 810kHz sitting in Abu Dhabi. I have posted it under AM/FM Tuners thread.

There is an overlapping station on whichever radio I try but there is also a local one in the background nearly all over the band. Were you able to make any of your TRFs selective? Would using a coupling coil instead of feeding in the IC from the tank circuit itself improve it?

It's good that you got the Elenco AM 780-K working. However, as you are currently experiencing, the TA7642 is tricky to optimise in the presence of strong local MW stations, which can hog a substantial amount of space on the dial. Thankfully there are no powerhouse stations in my part of the country. Also MW stations are on the decline in the UK and throughout a lot of Europe too.

A couple of years ago I took my DIY radio on a trip to London and experienced exactly the same problems you are facing from your local Abu Dhabi powerhouse transmitter.

From my experience, using a good quality ferrite rod, coil and tuning capacitor can sometimes help mitigate the situation by improving the inductance and Q factor. The TA7642 datasheet recommends an optimal inductance of 370 microHenries, if I correctly remember. An L-C meter comes in handy in these situations.

You can try connecting the antenna coil as you have suggested and adjusting the coil position along the ferrite rod. Another option would be to use a different ferrite and coil combination e.g. a coil with two separate interconnected sections.

Here is the circuit I am using in my DIY radios. It serves me very well and I can pull in stations from North Africa, Spain etc. after dusk. I have used a Mitsumi polyvaricon for tuning. The coil and rod came from an old radio.

 

[Subbu68]

It's good that you got the Elenco AM 780-K working. However, as you are currently experiencing, the TA7642 is tricky to optimise in the presence of strong local MW stations, which can hog a substantial amount of space on the dial. Thankfully there are no powerhouse stations in my part of the country. Also MW stations are on the decline in the UK and throughout a lot of Europe too.

A couple of years ago I took my DIY radio on a trip to London and experienced exactly the same problems you are facing from your local Abu Dhabi powerhouse transmitter.

From my experience, using a good quality ferrite rod, coil and tuning capacitor can sometimes help mitigate the situation by improving the inductance and Q factor. The TA7642 datasheet recommends an optimal inductance of 370 microHenries, if I correctly remember. An L-C meter comes in handy in these situations.

You can try connecting the antenna coil as you have suggested and adjusting the coil position along the ferrite rod. Another option would be to use a different ferrite and coil combination e.g. a coil with two separate interconnected sections.

Here is the circuit I am using in my DIY radios. It serves me very well and I can pull in stations from North Africa, Spain etc. after dusk. I have used a Mitsumi polyvaricon for tuning. The coil and rod came from an old radio.:

My post is here

Thread 'Another weekend project - MW TRF radio'

Oct 18, 2025

Early 1979, I used to go to a nearby bookshop to drool over a book on radios from Ladybird. Then in 1980 or so, my dad gave me a book written in Malayalam on radios that he used to build his first radio. It just said crystal radio, 1 transistor radio, 2 transistor radio and so on and in the Malayalam book it ended with a 6 transistor radio if I remember correct. Had no courage to ask him to get me the Ladybird book or components in the Malayalam book due to the situation at home then. Though the components were there at home in his build did not disturb it. Not brave enough

Then...

• Subbu68

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I have to get a LC meter. The circuit you drew looks similar to Elenco. They have used seemingly a regular MW coil and connected the main coil and coupling coil in series. They didn't say about adjusting the coil on the ferrite rod but I did it to tune the radio as accurate as others for the position of stations on the dial. Did try a 8inch rod from an old radio. It pulled in some Hindi broadcast station that I never heard. That rod I will keep for the superhet kit.

I came across a company Kanga Kits and they have the coupling coil separate. Another one Murania from the US uses a tickler coil. Have to try all that ..

More experiment to do....