Got a million dollar idea and hopefully more than $3 in execution
Grab a "few" (x553ish) Mullard OCP70s.
Phototransistors or sometimes referenced as photodiodes.
They're non-covered PNP germanium transistors. Each one was screened in manufacturing so no dead ones, all a pretty narrow spec.
Measuring a few dozen and I get betas of 55-80 with leakages of 100-~200uA. I say about because they're light sensitive. The peak sensitivity is near IR, so I read.
In my florescent basement , between light and dark I get little to no change in beta but in light I get a ~20-30% increase in leakage
Now, when you apply some light around IR spectrum, say a lighter lit 3 inches away, the leakage quickly shoots up. More light and the beta drops. Even more and the beats drops to single digits and... Leakage drops too.
Anyhow. I have some cool ideas to experiment with. Maybe make my first million.
Oh, and yes, from my reading, some OCP70/71S that were out of spec but tested in spec for OC70/71s were painted black and sold as such.
