I learned this C tune from a 1931 Okeh recording of the Mississippi old time string bad the Newton County Hillbillies, featuring Alvis Massengale on fiddle. It's a practice recording from a few years ago, uploaded for the 11/11/22 Old Time TOTW. I am three finger picking my 1928 Vega Tubaphone with a semi-fretless conversion neck, in double C tuning (gCGCD)