This is a very useful autotransformer circuit on the bench. We found it in the September 1970 Radio Elecronics magazine. The transformer must be according to what you want to feed at the output.
This circuit is from a publication from the 70s, but it can be assembled with any diac and a Triac...
Found in American documentation from the 1990s, this circuit generates signals in the 350 to 500...
This circuit was found in a Radio Electronics from October 1952. The circuit equalizes the sounds...