More fun with avalanche pulsers


 

I rebuilt the pretrigger and avalanche pulser onto one tightly packed board, and added SMA connectors for the output and the charge line to allow fast change. BNC for the ~65 volts from the power supply.
I'd discovered a GR 874 shorted termination in my bag of adapters, so I spent some time playing with shorted lines and reflections. Then I wanted to make a smaller toroid for the power supply - the junkbox one was (relatively) huge and wouldn't fit in a compact box. The Tek 130 LC meter got a workout figuring out AL for various cores. I was able to make a half-inch core work (think it was a T50-43) but the clock frequency required was high enough that it was getting into the unshielded pulser sitting next to it. An unknown green one saturated too soon and required very few turns - must be an iron powder one with high permeability. Finally a 3/4" yellow core (72 turns to get to 250 uH, that was tedious) worked at the original frequency and didn't cause trouble unshielded :)

A better RG-58 cable (SMA to BNC) worked well as a charge line, whereas a similar RG-174 cable was a droopy disaster. Putting the cheap BNC RG-58 cables on the end (with a barrel adapter) was also unsuitable. The "better" cable is too short by itself to be useful for risetime measurements on slower scopes, since the flat top is only about 3.5-4 ns long. As mentioned in the "3T77A tunnel diodes (again)" thread, I will try RG-402 (.141 semirigid) before calling it good enough. I doubt I have the skill or patience to build a really fast pulser to push the S-2(72 ps) or especially the S-4 (25 ps) to its limits.

Added a couple pics to the Sampling with 3S2 album of the breadboard so far and the pulse output.

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