I found that some BC107's produced more noise than others, also the Voltage over which noise was reliably produced altered from device to device. The upper and lower Voltage limits over which noise is produced could be quite limited in some devices. I found it best to test a few samples and grade them in order of noise O/P and widest operating Voltage over which noise is produced. i.e. The upper/lower Voltage thresholds over which noise is produced should be as wide as possible for reliable operation. About 10 devices had to be tested in order to select 2 which performed well as noise sources. I only needed one device but selected two so I would have a spare in case of failure. Click on the image below to see the full sized schematic.
The schematic is fairly self explanatory but as an additional guide here is an internal view of the completed unit which is built on strip board and housed in a small di-cast box. Click on the thumbnail below to see the full sized image.
Well, that’s about it, thank you for reading this and please send any questions, comments or "heckles" etc to the e-mail address linked below.