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Geo,

I would look forward to the same measurement but taken on a 6993 operating at 900V.

Maybe operates different from the Russkie's tube, or maybe not.....

I totally agree,wrt similarity of your result ~50V and Neon bulb..... I assume that Russian tube is a neon tube..... but 450V-50V = 400V is a long ways to slew in a (hopefully) short time. Depending on total parasitic capacitance (cabling, etc) the time it might take to do that would limit pulse rate quite a bit; I would think it would saturate at a relatively low count rate.... And maybe the 6993 is designed to improve on that???? I don't know.... I may look for some more datasheets for comparison.

I definitely don't understand everything I know at this point.

rogerw

Ah good. Somehow this important Topic got?"locked" last night. If a moderator did that please let me know. It's unlocked again.

Here's the latest and more critical look at the Bias HV drop across the SBM-20 GM tube operated at 450V via a re-regulator base from 920V DC from a Ludlum Bench "Geiger Counter".

First the last night report- updated?

"While attempting to clean up the workbench today, I had to look into this. Using a Russian SBM-20 (because it was on the workbench for a different project) and one of my 900 to 450V adaptor bases, scope attached directly across the GM tube (scope rated for 2000V), and a mantle for a source, the peaks on the scope showed negative pulses measuring f 450V P-P. At the "Geiger Counter" actually a (Ludlum 2500 Bench scaler) the P-P was 900V."

Looking again this morning with caffeinated eyeballs, a selection of eyeglass and more patience. Specifically looking to see if the "valley" goes all the way to zero before resetting. Best I can tell it does not go to zero, but the exact floor is difficult to determine with this 'scope, it seems to be somewhere around or just above 50V above ground. This would track very well with the NE-2 Neon Bulb analogy.? Someday (not this day for sure), we'll nail that down, with the storage 'scope, or someone else can.

By the way a GM tube activates with radiation because it is being operated on the knee of the gas discharge tube curve, in the Geiger region, and there is always a wide latitude of exact HV settings that allow that proper operation. + or - 50V or even more is normal, and is what Rad Techs call the "plateau" area (flat spot) of the curve.

Back to the discussion guys, sorry for the unintentional temporary lockout of us all.

Geo

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rogerw
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