The 1961 Zoning Resolution introduced provisions allowing in Use Groups 6 and 12 musical instruments to be played without obtaining a cabaret license, limiting the number of instruments to three, and restricting the type of instruments to "piano, organ, accordion, guitar, or any string instrument."
Use Group 6. Interestingly, the 1961 versions of Use Group 6 fails to mention dancing, most likely a drafting oversight.
Eating or drinking places, including those which provide outdoor table service or incidental musical entertainment either by mechanical device or by not more than three persons playing piano, organ, accordion, guitar, or any string instrument.
See Use Group 12 which does mention dancing.
Eating or drinking places, without restrictions on entertainment or dancing.
Use Groups 1961 Zoning Resolutions
page 110 Use Group 12