[Cryptech Tech] Alpha Avalanche Noise Block

[Fredrik Thulin]

...
> >> Speaking of voltage required for avalanche effect, you should consider
> >> part-to-part parameter variation. Transistors are analog components, if
> >> you buy ten BC818 transistors, they will all have different DC current
> >> gain. Because of this, if you have 10 identical boards, they may require
> >> slightly different voltages for avalanche effect.> 
> > They _will_ require.
> > So production boards with noise source should have possibility to tune
> > parameters for given source diode. We made that by putting set of
> > resistors into design and getting necessary voltage by short cutting some
> > of them.
> Emphasizing: set of fixed precise resistors. Never use any kind of variable
> ones. Never use 5-10% accuracy stock resistors

I don't get this, but I think it is because the circuit you are referring to 
worked differently than this.

In my tests, avalanche effects with BC-818-40 transistor starts around 9.5v.

At 10v, it seems to work but is slow.

At say 13v, I would be very surprised if it didn't work.

At 15v it should *always* work (famous last words).

So why not just pick something high and be done with it? Why bother with 
tuning? As I said, I think your circuit required that because it worked 
differently, but I don't think this circuit will require tuning. Let me know 
if I'm missing something =).

/Fredrik