Found in a1967 Ferranti documentation, this circuit uses an operational amplifier from that time. The circuit uses a LDR as a sensor and has a null setting.
This active crossover filter was obtained from the component manual used. Below is the performance...
This circuit is from an 80's documentation. It makes use of two SCRs with current capacity...
This interesting idea was found in a 1983 publication and is very simple to analyze, according to the...