Operational amplifiers power supply (CB21165E)

This circuit was found in National Semiconductor documentation from the 1990s. Operational amplifiers admit equivalents.

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Audio crossover filter (CB23743E)
We found this active crossover in a Radio Electronics magazine from June 1961. Note the different...
Output indicator 555 (CB20967E)
Found in Popular Electronics from the 90s, this circuit serves to indicate the output level of a...
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If you are on an old PC that you use for experiments, control or other applications, this circuit is...