Heath Zenith SL-122-02 Ten-Volt Lock-Nut Transformer Wired door chime transformer Lock Nut Type Input: 120VAC Output: 16VAC-10VA 1 year warranty 10-volt lock-nut-type transformer For use with single-chime doorbell installations Input 120-volt AC; output 16-volt AC, 10-volt ampere 2.25 by 1.875 by 2.5 inches