Mini AM radio transmitter kit from Ali Express: here a good power supply for it (schematic and demo)

Описание: Please read the description first to get the best information. Power supply for the ALI Express kit of a small AM transmitter, working between (say) 600 KC and 1.6 MC.

Earlier video about this ALI Express AM kit is here:
   • Mini AM transmitter kit for 800 KC - 1600 ...  

That upload was on 28 Jan. 2025, with an update on 30 jan. 2025.

Now and here ( 1 Februari 2025) it is about a useful (and a completely free of hum) power supply for 9 Volts at say 200 mA, that can be made with a wall transformer (12 Volt-300 mA) and a simple 1 transistor Voltage stabilizer, made with a BD 139 (NPN medium power transistor, current amplification factor, say Hfe, between 70 and 150).

In the published schematic you can see that you can switch-in a 9 Volt battery or the mains supply.

That mains supply works with an AC transformer, working on 110 V AC or 230 V AC on 50 Hertz or 60 Hertz.

The secondary output of that transformer is nominal 12 Volt. But, the open voltage, with its built-in bridge rectifier (inside that transformer) and a smoothing capacitor in the order of 470 uF (these are there in general) is (say) 16 Volt DC out.

With a lot of ripple and hum (50 Hz or 60 Hz) when such a simple wall transformer is used to give out a substantial current, in the order of 50 mA-300 mA or more. That is the reason of the now published power supply: completely free of hum, due to that 1 transistor circuit.

Please note (very important): I am NOT (!) talking here and now (1 February 2025, in this video) about wall transformers that work in a “direct way”, connected to 110 V AC or 230 V AC. Used to supply smartphones etc. They are NOT usable in this transistor circuit. They will simply stop to function, because they “see” a load that they do not “expect” in electrical/electronics terms, or they will give out an enormous HF noise.

I only talk about the use of a classical transformer, with a primary and a secunday winding, a steel laminated core etc.

About that ALI transmitter circuit on A.M.: you have to do the settings yourself: the AM frequency where the transmitter works, the modulation depth (3 potmeters), anyway, the right settings (AM frequency and modulation depth) can quite easily be found. Background noise is another issue: there are settings of these 3 potentiometers where the background noise is minimal.

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Upload 1 February 2025