This circuit was found in a 1967 US documentation. The circuit applies to modern general purpose transistors. The circuit has no offset. The power supply must be symmetrical.
This optical theremin was found in a 90s Hands-On Electronics. The basic frequency is given by C1...
Found in na 1970 EDN this circuit has a parallel regulation providing a symmetrical output of 15 V....
This receiver was obtained in a documentation from the 90's and is of the super-regenerative type....