In 1913, Edwin Howard Armstrong described a receiver system that used this effect to produce audible Morse code output using a single triode. The output of the anode, the output signal after amplification, was connected back to the input through a "tickler", causing feedback that drove input signals well beyond unity. This caused the output to oscillate at a chosen frequency with great amplification. When the original signal cut off at the end of the dot or dash, the oscillation decayed again and the sound disappeared after a short delay.