06-13-2011, 02:34 PM
Some have asked for a quick explanation of how this circuit works: the zener sets a fixed voltage (e1) below the B+. As the receiver is tuned to a station, the voltage at the load end of the 8K (e2) rises and approaches the full B+. This difference between these two voltages (e2-e1) lights the LED.
If an LED were simply placed across the 8K, the LED would become dark when tuned to a station, just the opposite of what's desired.
If an LED were simply placed across the 8K, the LED would become dark when tuned to a station, just the opposite of what's desired.
Pete AI2V
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