I got interested in making a home made type of Semiconductor made from in my case a galvanized nail .
I think its pretty interesting making an oscillator from a 2 pin device that you can make from junk .
How its made is you have to heat the nail with propane torch ,,,,,,on the other side around the nail zinc oxide is formed when it cools down and black spot of negative resistance you can see and some times not .
I also found if you don't have a torch a welder works as well with short welds to the nail it heats it enough to form the stuff .
Heres the circuit i am using apart from the rf part V cap and coil just doing AF ,the other coils in the picture are my magnetic amp transformers i am working on .
I am using more voltage than in the schematic 12 to 24 volts in the larger video you can see how touchy it is to adjust to get going ...also the wave form gos from nice sine wave to something a little more messy i suppose it could be the wire touching more than one negative resistance spot on the nail .
I saw one fellows design he had puts hes device in a large glass fuse to keep if safe ,i like that idea !
Most others i have seen doing this use galvanized sheets cut thin to make the device and i can say thin is good heating the metal would be harder if to thick ..it has to get pretty hot to the point the zinc starts to spit then you know its made the negative resistance dark spots on the metal ...
Simple thing but it is touchy to work out .