Some early models Solidtubes are very sensitive to AC fields. The induced hum usually goes away when you touch the body of the mic. To correct this:

FOR TECHS ONLY...NOT FOR CUSTOMERS!!

Remove 3 screw s from bottom of mic. Remove head cover by turning 1/4 turn clockwise. Solder a piece of braid between the two pieces of mesh used as a windscreen. It may be necessary to scrape the coating off of the mesh so the solder will adhere.