MightyOhm.com

As a follow-up to the other thread, just wanted to mention that I've succeeded running Geiger Kit at 1300+ voltage.

In this modification, I've done the following changes:

1) Q1: FJN330F with BUL216: The package is different and leads wouldn't fit into the holes, so it required some ugly soldering. A better approach would have been sanding the leads to make them round and thinner.
2) L1: 10mH with 18mH.
3) D1: 1N4937 with RGP02-20EHE3/54: 2kV rectifier.
4) C1 and C2 with their respective 2kV counterparts.
5) R8: removal, in my case, I've just used 0 Ω resistor instead.
6) VR1: replacing 10 Ω with 100 Ω for higher adjustment range.
7) R5: replaced with 560 Ω.

With above modifications, I could safely get around 1 kV stable output. To be able to get 1300+ voltage, input voltage needs upgrade from 3V to 4.5V. In my case, I've had to solder a different socket for 3 batteries. Doing so, R11 needs to go up to 330 Ω, but I haven't done this change yet (it works without it, albeit LED is a bit bright).

I have attached photo of the kit running at around 1300V. Note that my 10 MΩ multimeter is connected in series with 1 GΩ resistor, so the resulting voltage needs to be multiplied by 100, with roughly 1% of error.

Exciting result! Thank for for sharing the details of your modifications.

Thanks! Actually, removing ATTiny2313 chip and then applying 9V voltage to the whole setup (Timer chip works up to 15V but I wonder if that's a bit too much for 2N3904 or the one that I replaced it with, 2N4401), I could get up to 1900V from HV/TP1 with this same config, but that was quite scary! I wonder if there's a similar Atmel chip that can work with 9V...

In any case, with this config, the kit should be able to run any Geiger tube, including tubes requiring 950V or even vintage tubes that run at 1800V, assuming the whole setup can be run at 9V, which, by the way, fits into the space instead of batteries socket quite nicely.

By the way, if there are plans on providing new version of the kit, as a feature request, I'd ask for a bigger holes for Q1 to accommodate TO-220 package, bigger holes for R2 to accommodate properly voltage rated resistors (which are usually 1/2W or bigger, having thicker legs), separating power between High Voltage Power Supply and the rest of circuit, so you can use 9V battery to get up to 1900V at HV, while powering the rest of the circuit through 3.3V/5V regulator; the kit can probably be hacked to do this now, though.

interesting mod

are you planning to use it with photomultipliers for scintillation?

What type of Inductor are you using ? I am trying to get 500V but inductor of 10mH is saturating and a humming noise is heard from the Inductor, I am using Coilcraft 10mH Ferrite core inductor.