Just a followup from last night. I was almost right -- it's avalanche noise I was talking about with a *reverse biased* diode (or rather PN junction, which is what a diode is). http://willware.net:8080/hw-rng.html http://www.avtechpulse.com/faq.html/IV.8/ (I've seen diodes like what they show in that pic, only bigger at HVDC chopping stations) -A.