Point Contact(s) Transistor

Thread Starter


Joined Jun 17, 2014

You can make a point contact diode with a small plate of steel or iron that has rusted and a metal needle. The point of the needle has to come barely into contact with the rust on the metal plate.

Now the question is, could we make a transistor using two needles with points closely spaced?

I've made a point contact diode but just thought about making the transistor after someone asked a question about transistors on another site.
I did not try it nor look into if it would work at all. It would have to show some amplification.
This is more for the hobby value of course.

Thread Starter


Joined Jun 17, 2014

Just saw this thanks, ill read that.

The one on the left is what i had in mind.

Last edited:


Joined Dec 29, 2010
I scratched the paint off a OA70 diode and found that the germanium area is bigger than an 1N34A diode. It is not a welded junction like the 1n4148 diode but instead, there's a cat whisker like wire touching the wafer.

Here is a video I found on the net how to make a point contact germanium transistor at home...



Joined Oct 2, 2009
The semiconductor physics of a bipolar junction transistor is very different from that of two diodes placed back-to-back.
The impurity doping concentration between the base-emitter junction is very different from that of the base-collector junction. This physical difference is what makes the transistor work as an amplifier. In other words, the flow of charge carriers across the base-emitter junction is able to influence the flow of carriers across the collector-base-emitter channel.