I found tis circuit in na old documentation from 1958. The circuit uses germanium transistor availble that time and hard to obtain today. The circuit is indicated for phono applications using variable reluctance transducer.
This circuit was found in a 90s Popular Electronics. The sensors can be common speakers that reach...
This circuit indicates when a 28 V lamp burns, lighting a neon lamp with higher voltage. The...
This circuit was obtained from an American 80's documentation. The operational ones can be...