Designed for general purpose or replacement use (not Hi-Fi), in single ended, tube output circuits. Frequency response: 100 Hz. - 15 Khz (± 1db max. - ref. 1 Khz). (For full frequency response (20 Hz. to 20 Khz.) - see P-T1627SE). For push-pull output use, see P-T125A - optimized for push-pull tube output circuits. Open style with minimum 12" long primary & secondary leads leads. All sizes use butt stacked cores (using 29M6 steel) with an air gap, to reduce D.C. core saturation.