Circuit : Chad Castagana, Woodland Hills, CA 
Email : chcastaga@aol.com
First my apologies to Chad as he emailed his circuit in August 2019 and now I've just uploaded it. In this circuit John uses a Germanium type transistor as an active detector which has the added benefit of providing audio amplification. ge type transistor like OC71 are ideal for this type of circuit.An AM voice transmitter with variable tuning. The antenna circuit is also tuned and transmits via a long wire antenna. Please Note. It is illegal to transmit on the AM wavebands in most countries, as such this circuit is shown for educational purposes only.
NotesWhoever said "The pen is mightier than the sword", well thanks to Chad they were right. Proving that you need nothing more than pen and pencil to create a circuit diagram. The original circuit from Chad is shown below:
Chad's notes are below:
I have created a Germanium transistor circuit than can function both as a Diodic AM Detector, and/or as an active
solo-transistor amplifier for a radio receiver in the Medium Wave BC band.
Just uses a tapped air-core coil for its tuning inductance, no tuning capacitor needed.
Images of Chad's Work
As with all crystal radio sets, they require an aerial and Chad suggests a length of 20 to 25 feet of 24 AWG gauge wire. A ground plane i.e. a radiator or cold water pipe is also a good idea. This can be seen on the pictograph as the black wire with crocodile clip. Incidentally this receiver is for the AM band and will tune approximately 540kHz to 1620kHz. In Europe AM stations are separated 9KHz apart, and in the US and Canada 10kHz apart.
The circuit requires a single 1.5 Volt battery to power the circuit and can drive medium 2K to high impedance headphones directly. Chad has also used a 9 Volt battery with good results.