This version has the press-to-talk switch built in and was released in 1949 so this is probably from the early 1950's. Model 510S, known as the "Hercules". Fully functional, my tech ran through it and added a strain relief inside and made sure the switch and everything else was working properly, he put a new cord and jack on it as well.  Please see all photos for physical appearance.  These mics are ideal for harmonicas I am told.