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I've created a flavor of my small standards converter with the RF modulator built in for 441/30i AM audio and found it to work better than using a modern System M signal.
I used to run my pre-war sets using a standard System M modulator and Radio Shack amplifier as Eric mentioned, and the audio sounded fine, but there were problems. First, the audio in today's System M is typically 16db down from the video carrier while it was originally spec at 6db down. This means the audio is 3 times lower than it was originally. The second problem is with slope detection. While this method works surprisingly well, and can be low distortion if the slope is linear, the entire slope is typically less than 100kHz wide. The LO in these sets are not all that stable, so I found you have to constantly touch up the fine tuning while watching the set to keep the audio centered "on the slope".
By running the original AM audio carrier and at -6db level, there is no critical adjustment of the set required, and the audio sounds every bit as good as a radio from the time, and sounds better than with slope detection which can result in non-linearities due to the shape of the slope
Also, as Steve has already mentioned, the focus is not good enough on these crt's to be able to resolve the difference between 441 and 525. Running them at 441 does allow you to fill the screen, but does not change the apparent resolution.
Darryl
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