Pocket Tube Radio (T1621E)

This sensitive 4-tube, battery-powered receiver was found in a 1949 Radio Electronics. The circuitry was wired in crystal earphones.

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Bicycle Alarm (CB4365E)
This circuit was obtained from a 1986 Spanish magazine Resistor. The magazine no longer exists, but...
Reed Switch Alarm (CB885E)
Many reed switches can be wired in series to perform na efficient alarm as shoen in the figure....
Dial Tone Generator (CB5984E)
This circuit is from an old documentation making use of a 3,579,645 MHz analog color television...