Note
QST, May 1971, p. 127.
QST, Jun 1972, p. 149.
The Scrubber not a filter. It reproduces the CW note by using what the company called a "frequency responsive switch," or "fritch." The CW note is tuned to the frequency the fritch wants to hear (by means of a tuning meter), and the fritch drives a reed relay that keys an audio oscillator. That is the note you hear.