Fail first attempt (using replacement parts from Germany)

[elmo23x]

Hello Jeff and all the people here,

first, great job in your blog and specially with the Geiger kit. I have to say that I did not order it so I do not expect any support. I wanted to make use of the HV supply to drive a SBM-20, but my first attempt did not work (maybe the tube is broken? is there some way to test this?).

I started replacing some of the components (that are very hard to find in Germany):
* FJN3303F (replaced with a MJE13007 - VCEO 400v, VCEV 700v datasheet
* 2N3904 (replaced with a BC546B)

And for the inductor I used a 10mH Current compensated choke datasheet, which I am not sure it can do the correct job. It has two coils, but I only used one... and the other I left disconnected.

As power source I used a LM317 to generate the 3V from 5V or other source... (it works well, it gives stable 3.054v).

Turning the 10ohm pot the range I measure in the TP2 between 130-185v (with a fluke 180, I think the input resistance is 11,1 Mohm). This voltage in TP2 does not change if the tube is installed, and it looks very stable. I wonder if it is too low (Maximum is 185v, maybe I could replace R8 to a lower value? to get higher voltage in HV?). Unfortunately I did not find any shop with a gigaohm resistor

To detect the pulse I connected by now a led and a buzzer. They work if I short circuit, so I guess the detection is fine (unless the connection made by the tube is so short time that does not let me appreciate the light of the led or sound of the buzzer).

Any ideas on what I could test?
Thanks!

[elmo23x]

UPDATE:
I put 10 x 10Mohm (in total 100 Mohm) resistors in serial, plus the fluke. When the pot is to the maximum (or minimum resistance ) it reads 20.12v. So I guess I am generating only around 200v. Any tips on how to increase the HV voltage? Maybe reducing the resistance of R8? I will try this later... and lets see if it blows

[elmo23x]

UPDATE 2:
I decided to remove R8 (short circuit), and when I set the 10ohm pot to 4.2ohm, I measure 30.1v with the 100Mohm set of resistors. Now the tube is being activated by the background radiation, but I am not sure what other modifications I can do to get a big higher voltage. If I reduce more the resistance of the pot the HV stops working.

[mightyohm]

The HV transistor characteristics will affect how the circuit works quite a bit, so I'm not too surprised that the replacement isn't giving identical results. Are you using the correct diodes, at least? Is your 555 a CMOS variant like the TLC555?

Do you have an oscilloscope you can stick on various nodes of the circuit? That might help troubleshooting.

Are you building this on a breadboard? If so, you may not get good results no matter what you try.

[mightyohm]

Also, your inductor is suspect. It may not have a high enough saturation current. Try other 10 mH inductors, preferably one with a single winding!

[elmo23x]

Yes, the diodes are the same, and the 555 is a TLC555 and I am build of one of these resin boards with metal contacts to solder (I do not know the name of it). Unfortunately no access to an oscilloscope

The first thing I am going to do is to replace the inductor with a different one. I found this one in a shop nearby (it looks a bit "different", see the picture):
f MHz: 0.15 MHz
R: 105 Ω
I: 48 mA
Induktivität: 10 mH
Resonanzfreq: 0.36 MHz

I write this data because I am not sure what other characteristics I should look for in the inductor. Thanks again!

[mightyohm]

That inductor may work, but the current rating is a bit low and the series resistance is quite high.

Here are the specs for the inductor used in the kit:

R: 18.8 Ohm
I: 80mA
Inductance: 10mH

I'm actually not sure what the resonant frequency is, but here is the datasheet: http://industrial.panasonic.com/www-dat ... 000CE2.pdf