Re: Avalanche Pulse Generator: Chassified

On Aug 23, 8:54 pm, "Tim Williams" <tmoran...@xxxxxxxxxxx> wrote:
Complete schematic:http://webpages.charter.net/dawill/Images/Avalanche%20Pulse%20Generat...

[...]

My question: I'm only getting 8ns pulses, quite well defined on my 200MHz
oscilloscope. Also, they only occur (even at ~110V) when the sync amp is
pulsed. Is the 5pF base coupling cap too much? Did I put it in the wrong
place (in terms of the voltage that moves around it)?

I seem to recall Jim Williams' had ferrite beads on that lead...

I may've just answered my own question, but even so, that doesn't explain
why it isn't relaxation oscillator-ing. The base resistor is about right,
based on experiments /on the freaking breadboard/, which worked better than
this. I changed the 2N3904, so I'm pretty sure it's not trashed.

What's more, adding an open line to the Pulse Line jack stretches the pulse,
but expoentially. It grows one ugly-assed tail. I know matter-of-factly
that lines will discharge into lines, forming nice flat tops, so there's
something fishy here.

Tim

Tim, that's an awful lot of emitter degeneration you've got on the
avalanche transistor, especially if you want short pulses. I'd wonder
if that discourages the avalanche cascade. Might that be a factor?

I tested various transistors in avalanche some time back--I'll check
my notes on the 2n3904.

Cheers,
James Arthur

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