I have build the following circuit on a stripboard
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.
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.