This simple general-purpose transistor mixer was taken from an article in Electronics Now magazine in March 1994. You can choose a low-noise transistor such as the BC549.
The circuit is from a Radio Electronics magazine from October 1987. The Triac must be equipped with a...
I found tis circuit in na old documentation from 1958. The circuit uses germanium transistor...
Today we have more compact solutions. This is from a Radio Electronics magazine from October 1990....