Old-time - what are the typical keys (modes, tonal centers)?
At first this may sound like a dumb question. The obvious answer is that most jams play tunes in D, G or A, and sometimes C. I get that.
But does that really mean that most major sounding tunes are in D-ionian, G-ionian, A-ionian, A-mixolydian or C-ionian...and that most minor sounding tunes are in either A-dorian or A-aeolian? (ionian being another word for the standard major scale, aeolian being another word for the standard minor scale).
In other words, there don't seem to be many minor sounding tunes with a tonal center of G or D...usually the minor sounding tunes have A as the tonal center but the major sounding ones could have D, G, A or C as the tonal center. Would you concur?
Re: Old-time - what are the typical keys (modes, tonal centers)?
I don't know for sure, but I would be willing to bet that the relative minors or all the keys you mention would be the most popular. For example, A minor is the relative minor of C major. E minor seems like the other obvious one (relative of G major).