Here I will show the most simple radio circuit using twin triode, 3A5. 3A5 is a direct heated twin triode with 3V heater voltage. Twin triode has two unit in single tube and we can use, for example two function as we wish. The circuit is very simple as shown in the above picture. Firstly, the resonator consisting L2 and C3 selecting receiving signal and the RF signal goes to grid (#3). After RF amplification, signal comes out from plate (#2) and entering rectifier consisting of two diodes. Before entering rectifier, L3 and R3 are inserted for plate voltage biasing. This is just a prototyping and I just use 200k VR in order to find best receiving bias (indeed, without design...). After rectified, audio signal goes into grid of second triode (#5) and now audio signal is amplified and goes out to earphone output. No, it is not regenerative nor reflex, purely no feedback circuit.

I quickly wired the circuit on breadboard. As for the power supply for heater and plate voltage, My all-in-one power supply driven by Lipo will be useful and handy, but also we can prepare by series connected 006P (9V) battery or something.

Here is the quick demo of this simple radio. It cannot drive speaker and powered speaker is connected, but as you see, it works! If you try, please set two wipers at middle position, and slowly change them to get optimum point. Yeah, it works! Not so difficult but we can enjoy great heritage!!!