Explorer for all ranges (T1098E)

This circuit was found in a Radio Craft from October 1946. Power supply not shown, and tubes are 1.5V filament types.

Locked resonant relay (CB8840E)
This circuit uses a resonant reed relay to recognize the frequency of an input signal. Adaptations...
Constant Current Source II (CB19950E)
The operational used is uncommon today, but equivalents can be used. Unlike the previous one, this...
110 V or 220 V Voltage Indicator (CB16899E)
This simple circuit uses a zener diode and two LEDs to indicate whether the voltage of a power grid...