Junction Noise

[Martin Czech]

:::particularly more amplitude, but all of a sudden the pesky
:::60 cycle stuff I was seeing on the scope is gone.  I
:::tried several PNP and NPN transistors and I kept getting
:::60 cycle hum mixed into the noise.

The collector leg is usually left open. I wonder what kind
of effects are possible due to that. It should be better
to connect collector to base.

OTOH it could well be that the diode has much more noise
that the transistor thus swamping any 60Hz interference.

Maybe this and a variation in mechanical construction
(well, three legs instead of two) are the reason for your
60Hz problem comming ind disappearing again.

However, such noise circuits have high gain, so a
good shielded (aluminum) case is a good idea.

m.c.