Repairing a DIY Geiger Counter

I ordered this DIY Geiger counter online. It arrived in good time however it was damaged, the buss fuse holders were crushed, and the J305 Geiger Muller tube was destroyed. This was a problem since I used my points from earlier purchases from this online retailer to buy the DIY Geiger counter, it cost me less than a new compatible Geiger Muller tube.

As I negotiated with the seller about the damaged kit I decided to find out if I can repair the Geiger counter with what I have.

All but the SI3BG Geiger Muller Tube was salvaged parts.

I do have a SI3BG Geiger Muller tube; but I didn’t know if it would match the Geiger counter and of course the data sheet is a jpeg in Russian.

In order to just copy and paste I duplicated every line of the Russian datasheet in word and inserting Cyrillic symbols.

Then using google translate I translated every line of the datasheet. Although this wasn’t perfect and I had to figure out a couple symbols, I now could make an English datasheet.

With an English datasheet I compared the specks of the SI3BG Geiger Muller tube with the J305 Geiger Muller tube.

Other than size and sensitivity most of the data was close enough that the SI3BG tube should work.

Drill

Small drill bit

Dremel

Multi Meter

Soldering Iron

Spring Loaded Tweezers

Solder

Buss Fuse

Fuse Holders

Duel Male crimp connector

Duel Female crimp connector

Sandpaper

Remove the nuts from the short standoffs on the circuit board.

Screw the long standoffs that came with the kit to the short standoffs on the circuit board.

Place the acrylic cover on top of the long standoffs and screw it down tight with the nuts you removed from the short standoffs.

Once I placed the acrylic cover on the long standoffs; I discovered the high voltage pot’s adjustment screw and the inductor were pressing up on the acrylic cover.

To cure this I added two soft washers and one metal washer to each of the long standoffs making the acrylic cover clear the high voltage pot’s adjustment screw and the inductor.

I wanted to keep the acrylic cover in place to protect the Geiger tube when I was doing experiments with the Geiger counter and to protect myself from high voltage shocks. To do this I wanted to cut a space over the P3 and P100 pins for connecting to devices like Arduino to the Geiger counter. I also wanted a hole over the high voltage pots adjustment screw to adjust the high voltage if I needed to.

I marked the placement of the high voltage pots adjustment screw with a Sharpe and I marked the pins with a small sticky label.

Using a had drill I drilled out the hole for the high voltage pots adjustment screw and using a dremel with a small saw blade I cut out the hole for the pins.

Last I reinstalled the acrylic cover to check the fit.

It took me a bit to find the parts to make an adapter just the right size. I used a double male crimp connector, a double female crimp connector, the end of a buss fuse holder, and the end of a disassembled buss fuse.

Using sand paper clean the buss fuse end and the double male crimp connector

Using a spring loaded tweezers I held the end of buss fuse to the double male crimp connector and solder the two together.

Assemble the adapter by slipping the double female crimp connector on to the end of a buss fuse holder.

Then slip the double male crimp connector on to the other end of the double female crimp connector.

If you did it right the adapter should just clip to one end of the Geiger tube and the whole assembly should clip right into the circuit board.

You can adjust the high voltage with or without the acrylic cover on.

Set your multi meter for the highest voltage.

Connect the positive probe of the meter to the positive side of the Geiger tube.

Connect the negative probe of the meter to ground.

DO NOT CONNECT THE NEGITIVE PROBE TO THE NEGITIVE SIDE OF THE GEIGER TUBE. It will cause the Geiger counter to squeal like a banshee and the indicator LED to light up.

Then adjust the voltage up or down as needed.

Although the datasheet recommended a higher voltage, the highest voltage I could get was 215 volts.

Adjusted right you should get a tic about every second or two from background radiation.

To see if the Geiger counter works you can test it with this radioactive ionization chamber from a smoke detector.

Place the ionization chamber next to the Geiger tube. The Geiger counter should go from about one tic a second to about two ticks a second.

And you are ready to experiment just make sure everything is tight.