Radiation Detector With Geiger Muller Tube
For ages I have wanted to build a radiation detector using a Geiger Muller tube. No real reason, just wanted to build one. I purchased a tube from ebay and set about designing the detector. The only design goals where it had to run from a single cell (1.5V) and be built from what I had.
The left hand side of the diagram is all power supply. It generates about 380V from the 1.5V cell. It draws around 2mA from the cell.
TR1 has three windings. About 1500 turns form its secondary, 12 turns each for primary and feedback. The output is trippled and regulated by feedback through the neon bulbs. The 'neon bulbs' I have aren't neon because they glow green due to a phosphor coating, probably emitting UV. Ideally these 'neons' would be zener diodes, but I don't have any with a high voltage knee.
The pulse duration from the tube is extended by Q4 & Q3 to provide a good 'click' from the speaker. The speaker I used has a coil resistance of 45 Ohms.
All transistors are BC550C and BC560C, these have quite a high gain and substitutions with a lower gain device may need some tweaking.
Here it is built...
It doesn't have a CPM meter yet, that will come later.
