MFJ-557 Mod
I got an MFJ-557 Morse Code oscillator from the estate sale of an SK Ham for $10. According to the Owner’s Manual, if you want to connect the straight key to a 12v radio, you have to remove the oscillator from the key and attach a cable for the radio. Also, the oscillator circuit is nearly the same as my Morse Code Oscillator, and it will draw current from the battery even if the key is not down. In order to overcome these two problems, I decided to add a DPDT switch and a 3.5mm jack to the oscillator box. A schematic is shown below.
© 2012, Stephen Denison
Last Updated: September 30, 2012