Adjustable Notch Filter (CB14918E)

This circuit was found in an old Poptronics. Operational amplifiers can be replaced with equivalents. The power supply must be symmetrical.

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Simple timer (CB23641E)
For times in the range of seconds to a few minutes we found this timer with the CK722 in a Radio...
Negative Current Regulator 7905 (CB15340E)
We found this circuit on Motorola Linear Interface ICs from 193. Other circuits in the series can...
Audio Micro Oscillator (CB21921E)
This oscillator was found in a Raytheon documentation from the 60's. The phone must be high...