I saw this fascinating picture of Sinclair MW match box sized 2-Tr radio, named Micromatic, in Practical Wireless way back in 1967-68. It was claimed to be the world's smallest radio that time.

The circuit diagram is as given below. Antenna coil is wound on a small ferrite rod. TC1 is a compression type trimmer for tuning the MW stations.

It is basically a reflex rengen receiver. The first transistor amplifies the input signal that is detected by two Ge diodes D1 and D2. The detected audio is fed back into the base of Tr1. Direct coupling of the detected signal to the base also acts as the AGC. The correct regeneration is obtained by feed back from choke to the antenna winding. The position of the choke is important.

The audio signal is further amplified by Tr2. A high impedance head-phone is used for the output.

I made a similar MW radio during Asian Games in 1982 for sports news and commentary. It worked really well!

Since high impedance head-phones were not easily available those days, a third transistor was introduced for lowering the ouput impedance. The circuit diagram is given below. The detected audio was AC coupled to base of Q1 for reflex action. A small PCB was used to mount all the components. The position of the choke was critical. The optimum regeneration was obtained by moving the antenna coil sideways on the ferrite slab.

The radio was switched ON by inserting the headphone plug into the socket. This was made possible by modifying the socket contacts by bending!

Can you recognize this ??

This is Galena Crystal.

Galena is a semiconductor mineral to make crude point contact diodes.Discovered in 1904, these were used in radio receivers till World War II. These are still quite popular with hobbiests and radio amateurs! You can purchase these on Ebay.

The above crystal is my priced possesion since 1960. Salvaged from my elder brother , Dr Pradeep Gupta's (now W6XH) crystal radio during his B.Tech from IIT, Madras during 1957-62.

The above pictures show the assembled PCB and the overall layout of the radio. A 2X gang was used for tuning the MW stations.

A few number of finished/semi-finished MW Transistor Radios are still lying with me. If you are interested in tinkering with reflex rengen receiver, you are most welcome to collect these - free of cost!!