Hammond 124D 7K/15.8K Centre-Tapped Tube Driver Interstage

The 124D is a 5 watt tube driver interstage transformer with a centre-tapped 7K ohm primary and a centre-tapped 15.8K ohm secondary. It is listed for push-pull circuits and belongs to the 124 Series, designed for general purpose or replacement use in push-pull or phase inverter tube driver stages. Tube amplifier designers and restorers will find a 1:1.49 turns ratio and a split primary useful for driving output stages.

The core uses grain-oriented silicon steel laminations. Typical DC resistances are 218 ohms (BLU - RED) and 236 ohms (RED - BRN) across the two primary halves, and 297 ohms (GRN - BLK) and 394 ohms (BLK - GRN) across the secondary halves; the ordering table gives totals of 454 ohms primary and 681 ohms secondary.

At 1.0 kHz and 1.0 V the 124D measures 6.45 H primary inductance and 14.4 H secondary inductance, with 0.125 H leakage inductance. Measured impedance at the same conditions is 40.5 kOhm primary and 90.25 kOhm secondary. Dielectric strength is 500 Vrms and the unit operates in the 150 Hz to 15 kHz range.

It is an open style, 2 point mount transformer with minimum 5 inch leads. Outline dimensions are A 2.81 in (71 mm), B 1.46 in (37 mm), C 1.68 in (43 mm) and D 2.38 in (60 mm), with 0.19 in (5 mm) mounting holes. Shipping weight is 1.2 lbs (0.54 kg). The series has no gap for DC bias current, so it should not be used for single ended applications. The part is RoHS and REACH compliant and marked Made in Canada.