Friday, November 16, 2012


This is a MFJ-557 Deluxe Morse Code Practice Oscillator with Key mad by MFJ enterprises. They still make this model. It has both tone and volume dials and a built-in speaker and the key has adjustable contacts. It's got a nice heavy base so it doesn't slide around like most practice keys. It runs off a runs on a single  9-volt battery.  I have no idea how old mine is, I bought it at a yard sale for $5. I would guess it's at least 20 years old from the rust popping the chrome on the key. I pried out a rotten battery and replaced the toasted 9V connector and voilĂ  a working key.

Code Test

The fun part for me isn't Morse Code practice. For me it was the fun of wiring the 1/8" output to a phono preamp and inputting it directly into the Hauppauge Sound Blaster sound card of my desktop computer. The wiring is fugly, but it works. (Unlike a recent failed experiment with my Wollensak microphone) The real fun is that the tone dial makes this instantly into a circuit bending instrument. A tone dial is a pitch bender, and an oscillator is also a tone generator. In other words this is $5 of pure fun.