Following are circuits for sending good MCW. There is a short write up included for each one.

Figure 1 shows a keyed phase shift, or "twin T" oscillator. This one produces a very clean signal with accurate shaping and pure tone. It has enough output voltage to connect to a mic jack, but not enough to drive a speaker. Figure 2 shows a simple one chip amplifier for driving a speaker.

This type of oscillator is used in the old Collins 32S-1 single sideband transmitter to generate CW. It is also shown in editions of the ARRL Radio Amateur's Handbook as a test source for audio signals. I recently noticed that Lew McCoy (W1ICP) used it as a retrofit for MCW on the old "Benton Harbor Lunchbox" series V.H.F. tranceivers in a 1972 edition of the ARRL Radio Amateur's V.H.F. Manual. The basic oscillator circuit is not a new one.

Article & Schematic for Figure 1 & Figure 2

The second circuit (Figure 101) is a simpler one that will drive a speaker directly. I found this one in an ARRL "Hints and Kinks" as a practice set. I noticed that when a few parts were added, it produced a pretty good sinewave. Adding a few more parts allows fairly good keying characteristics. I think this one represents the minimum requirement for good MCW.

Article & Schematic for Figure 101

I don't recommend coupling a square wave to the mic jack, or holding the microphone up to a buzzer, doorbell, or other sound producing device such as the sidetone speaker on a keyer. Some ops own a keyer with sidetone, or a practice set with square wave output. The signal from these can be filtered to a sinewave and then fed into the mic jack of the MCW transmitter. There will still be no proper shaping of the keyed waveform, but it will work in a pinch, and sounds much nicer than the square, or triangular, wave often found on side tone generators and practice oscillators. Figure 4 shows a filter that works on my "Trac" brand electronic keyer sidetone output to produce a clean sinewave.

Schematic for Figure 4

Figure 1 works the best, but these other ideas can work OK, too! Drop me a note and let me know how these circuits work for you.