I love these old tunes!
You can use the “YouTube Video and Audio Downloader” plugin to save an mp3 audio file from these videos.
I have an old 1931 tombstone style table-top radio that I use as a speaker to listen to this sort of old music...it adds a nice touch to the experience :-)
I use KeepVid.
Go to www.keepvid.com
Drag the “bookmarklet” to your bookmarks bar.
When watching a YouTube, click on the bookmark.
Another tab will open up, with links for downloading various sizes of the video.