Larry Hartke has a Big Bass Showroom inside the Sam Ash Super Store on 34th street in mid-town Manhattan. Pop in and see him. They have most everything there. https://www.facebook.com/larry.hartke?fref=ts
It does not appear to have tweeter on/off switch at all. Here's link to the owner's manual http://www.samsontech.com/site_media/support/manuals/HD75_HD150_5L_v2.pdf and the HD 75 webpage http://www.samsontech.com/hartke/products/combos/hd-series-combos/hd75/ And you can call Hartke's parent company, Samson at Phone: 631-784-2200