Electronic – Op Amp Oscillation BPW34 Radiation detection

operational-amplifieroscillation

I have build the following circuit on a stripboard

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Now the problem is, even if I do not have the BPW34 diode attached my output shows a nice sqaure wave as you can see here
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But I have no idea where to start how to analyze where this comes from or why this happens. So I am very grateful for any ideas how to approach this problem. One addiational thing: I did not use the 330k Resisitors instead I used 300k resistors. Edit: The transistor is a BF245B.

Here you can see my stripboard. enter image description here

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This blue thing in the upper picture is a capacitor which is not connected. And remember: The BPW diode is missing but when it is soldered on the board and made lightproof it also starts oscillating with the same frequency and amplitude.

Best Answer

Look at the original PCB design from Elektor: -

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It's a double sided board with a full coverage ground plane on the component side and a partial ground plane on the solder side. These ground planes are probably quite fundamental in achieving low noise and stability given that the circuit has an AC gain of 900.

You'd have to be at the top of your game to make this work consistently on strip board or just plain lucky.