The closing of Johnny D’s Uptown in Somerville left a big hole that needed to be filled. For decades, blues musicians jammed on that stage on Sundays. Some big names grew up on that stage and everyone supported everyone else. That is the spirit that The Porch fosters with its weekly People’s Jam. Bass amp and two guitar amps provided. DIs, vocal mics, horn mics provided. Just come on in, add your name to the signup sheet. Each group of jammers plays three songs and no one repeats until all the players have had a turn. Admission is free.