3 transistor AM radio 700 KHz - 1.6 MHz

The radio works on 12 Volt. A simple radio usable for local radio stations on AM between 700 KHz and 1.6 MHz. You need an external antenna from approx 10 meter outside or an indoor antenna from approx. 4 meter. Connect an indoor antenna directly to the base from the first transistor ( max. 2 meter long) or use a coupling capacitor between 100 P and 500 P (2 - 4 meter long). Experiment a little bit with the antenna capacitor. With a 10 meter long wire antenne outside you can receive radio stations from approx. 600 km or more far away. I received radio China, a radio station from the US and radio stations from eastern europe. The second transistor has two functions: tuning + oscillator. In the oscillator mode the oscillator is modulated by the antenna signal. This gives a better selectivity and better receiving results. You can find more sophisticated + easy to make radio schematics (superheterodyne) in my books (author Ko Tilman), "Retro Radio" (Dutch text), published by Elektor International Media in the Netherlands, and "2-10 MHz Shortwave receiver and 1 transistor VFO's (published by Lulu on the Lulu website). Corrections to the video: BF 547 b = BC 547 b, "condensator" (Dutch) = "capacitor".

[@radiofun232]

Thanks Andy, never thought about it as a multilayer breadboard, but it makes sense. Indeed it is fun to make these circuits and I am always thinking about new figurations.

[@Mushketer888]

Those soviet tube capacitors are most usable in HF,VHF,UHF etc operations They have very good stability!

[@AndyDaviesByTheSea]

Hi there, it looks like you’re having a lot of fun with your radios. Seeing the double layer of ‘bread board ‘gives a different meaning to the term, ‘Multi layer’ boards, hi hi. Well done, nice demo. Kind Regards ... Andy

[@radiofun232]

It needs further amplification by means of a 1 Watt audio amplifier. In the video I used a 1 Watt audio amplifier and a real loudspeaker box to give the sound a certain quality.

[@radiofun232]

I bought the white 1000 P capacitors on a radio flea market. They were made in Russia. All ceramic caps from 1000 P will work too.

[@28noch]

Very cool! Congratulations for video! Brazil vintage radio fan.

[@radiofun232]

28noch thanks, and it works:)

[@Lechoslowianin]

Quite an interesting layout. I think I'll try to do it. However, I do not understand why some resistors are connected two in parallel and in series

[@radiofun232]

The reason is that all my circuits are experimental circuits, though very well tested. Aim is always to make it in such a way that everyone (YT viewers) can reproduce it with success. So in some cases one or more resistor/capacitor values are tested to make it (better) reproducable. That is why you see these "remnants". 5 dec 2020.

[@Lechoslowianin]

@@radiofun232 That's what I thought. Thank you

[@stephenwilliams5201]

Ja! Ist gut! Danke.

[@Electrophile-d4w]

I think it's a regenerative receiver

[@amiakash5037]

Hi, I love your videos. I have all those old parts. Big resistors, big capacitors (pipe like), from the University. I guess they are from 70s? Anyway I was looking to make a simple AM receiver using 2 or 3 transistor and this looks the best circuit I can make. By the way can you suggest how to modify the circuit for Long wave receiver? By the way are you from Netherlands? Cheers from Utrecht..!!

[@radiofun232]

I never made a long wave receiver, but saw many schematics where they were made as a not-supethet receiver. So very simle : a coil on that Long Wave frequency band + tuning capacitor, FET as a first transistor, then a 2 transistor amplifier (2 x BC 547b) can be simple, freq. is low, and then the AM detector (germanium diode like the 1N90 or 0A81 or oA85). Yes, I am from the Netherlands. You can find these circuits on the internet, I am sure.

[@mre521]

What is the operating principle of this radio? I can tell that the first and third stages are rf amplification/buffering and amplification/detection respectively but I am unclear on the second stage. As you have explained (and I have experimented) the second stage is a VFO but I fail to see how a VFO alone makes a receiver. Is this second stage a self a oscillating mixer? If it is then how does the receiver work with no IF stages? It is not a superhet. Since you say it is a "direct/heterodyne" receiver it sounds like it might be direct conversion one. From what I've read direct conversion receivers need a PLL to operate correctly so how does this work? I am going to build and perhaps then it will be clear how it works.

[@radiofun232]

mre521 It is indeed a quite strange setup that I found during experiments. But as far as I could see it works this way: the oscillator is set on the frequency that you want to receive and it is modulated by the antenna signal, received on that same frequency. In fact I don't know where the AM signal is detected. As far as I know from the radio theory a radio where 2 forces are active is called a heterodyne, so that is why I named it that way. It is indeed no superheterodyne.

[@mre521]

After a bit more reading it seems that your design may be some type of regenerative receiver (en.m.wikipedia.org/wiki/Regenerative_circuit). From that page it seems to indicate that the bias of the oscillator stage could be changed to act also as a detector and do away with the OA91/Ge diode to reduce the parts count further.

[@Berghiker]

Nice radio. Where did you get the special tube capacitors from? Will ordinary ones work too?

[@tonywright8294]

Yes

[@salimkumar9748]

Thanks

[@faisalabbas0869]

This is allmost 12 years old video can thes all r station inactive?

[@radiofun232]

In the Netherlands there are no longer public radio stations on this AM band. There are only 2 local private radio stations now, with limited power. 16 feb. 2023.

[@fredymredy]

I see two C2 capacitors one is tuning and one is ceramic cap, but if i want to put tuning cap i need to remove the second C2 ceramic cap. ?

[@radiofun232]

fredy mredy L1 and L2 form a tank circuit that has to resonate on the received frequency on the antenna, so it must be tuned. The tuning is affected by 3 things: the amount of turns (L1-L2), the ferrite rod that can be moved in and out of the coil and the capacitor C2. As far as I can see I used a 1000 pF capacitor (fixed value) for C2. The tuning was done by the ferrite rod. With 2x C2 in the schematic I tried to indicate that you can both use a variable capacitor or a fixed capacitor. Wit a tuning cap you can also tune in to a certain radio station.

[@erikdevriese671]

+radiofun232 To me it is obvious that your receiver is regenerative in nature and that the bias setting of the first transistor stage is actually pushing the feedback loop (via the secondary coil connected to the collector) over the threshold so that the amplifier becomes an oscillator, enhancing the Q of the tank coil. I'm not sure what the function is of the 8 pF emitter capacitor but since it is in series with the emitter/base capacitance it appears akin to a Collins oscillator configuration (see Kainka's site for similar radio circuitry. Be what it may, I'm a fan of your site. Keep up the good work! ON4ADV

[@AtomicElectronCo]

Does it really matter if u make it with BCA547A, BCA547B, or BCA547C? I know the limits are somewhat different, but I'm not sure how it would affect this application.

[@radiofun232]

No it does not matter, but I always had the best results with the BC 547b. As far as I know their Hfe (Beta/amplification factor) differs somewhat, but I always use the BC 547 b. This is, by the way, the best small signal-low voltage transistor for electronic experiments and success is "guaranteed" in many projects. It can even work as high frequency transistor (though not designed for that application), up to approx. 9 MHz. This also applies to the PNP brother from the BC 547b, the BC 557 b. Also a very successfull transistor.

[@AtomicElectronCo]

radiofun232 THANKS A LOT for your advice. I will buy a dozen pair from China and see how far they go!

[@Mushketer888]

radiofun232 what you can say about BC547C,2N2222 and 2N3904? BC547C has hfe aprox 400-500 is it better for electronics? another question about hfe... for example if i want to choose other transistor model in original schematic, which is the best(i would say universal) hfe? around 100-200?

[@radiofun232]

Ilja Lebedevs My answer is: try the transistors that you have in stock. I think the BC 547 c will work too. The amplification factor is important but too much amplification can lead to instability. I never use small signal transistors with a beta between 400 and 500, in such cases I build 2 transistor stages and set both stages to the amplification that I need. The 2N222 is also a usable transistor (test its Hfe first), I never used the 2N3904. Though this says nothing, could be a usable transistor too. Amplification is important, 200-250 is good for smal signal circuits, audio,radio, etc.By the way: this is the max value, in real the amplification must be adapted to the situation, to "what you want and need". Amplifying 1 mV to 100 mV can be done with a transistor with a Hfe of 100. A radio signal at a receiving antenna is approx. 5 uV (micro Volt).

[@radiofun232]

Ilja Lebedevs As you can see this is a heterodyne radio. There is an oscillator in it. Perhaps this oscillator will not work with the 2N2222, but it is possible that it oscillates with a 2N2222..

[@رأفتالهيتي2]

Nice video de Yi1hxh rafat 73 from baghdad

[@radiofun232]

73 the PA11319 from the Netherlands :)

[@davidharmon8745]

Do you have it hooked to a amplifier.

[@radiofun232]

Yes, it is.

[@davidharmon8745]

Where did you get a diode that would work.

[@radiofun232]

Most of them on radio flea markets. Though the 1N90 (Germanium diode) is still available now via ebay or so (2022). The 1N34 is still in production. You can also use other types of small signal Germanium diodes.

[@davidharmon8745]

@@radiofun232 thanks.i bought some 1n34 on Amazon. But none would work.itred some from old rca tv an other electronics. I just get hum.

[@radiofun232]

@@davidharmon8745 That is very strange, how did you use them and in what kind of circuit?

[@davidharmon8745]

@@radiofun232 crystal radio with coil an tuner cap .bojack 1n34a didnt pick up.i wonder if it would work with a guitar amp

[@radiofun232]

@@davidharmon8745 This can help perhaps: a 1 transistor more or less universal pre amplifier, also for a guitar amp. Video link kzbin.info/www/bejne/bXqrm4ybqLJqi68 Can be supplied out of a 9 Volt battery in case of a guitar amplifier.

[@西小凡]

这个电路可以改到7MHz短波里吗？

[@radiofun232]

HI, I don't read your language. When you ask whether the circuit is suitable for 7 MHz: it is not suitable for that frequency.

[@mustafaavci4362]

Hello it's good.