City Clerk William Campbell recently announced the calendar for the 2013 city election. Woburn voters this year will elect the mayor; all nine aldermen; and five School Committee members. Nomination papers will become available on May 1. The deadline to take out nomination papers is July 26 and to return them, July 30. The city will hold a preliminary election, if needed, on Sept. 17, with the final election scheduled for Nov. 5. Candidates must file 100 signatures to run for mayor; 50 to run for alderman at large or School Committee; and 10 to run for ward alderman.