Hammond 850LA Sealed 5K/20K Bridging Audio Transformer

The 850LA is a sealed, broadcast-quality 850A Series transformer for output to line, matching or bridging. Its high-impedance 5K/20K ohm primary steps down to a 150/600 ohm secondary, so it can bridge across a line or match a higher-impedance output stage to a 600 ohm class line. Nominal winding resistance is 2240 ohms primary and 69 ohms secondary (+/- 20%).

The part drawing specifies frequency response of ± 0.7 dB max. from 20 Hz to 20 kHz (the series sheet notes units over 5K ohms may be down 1 dB at 20 kHz), typical output power of +15 dBm (31.623 mW) and distortion below 1% at 20 Hz under full power. Typical DCR is 760 ohms (BLK–WHT = BRN–ORG) and 30.5 ohms (BLU–RED = GRY–YEL), dielectric strength is 250 V RMS, and primary inductance is 13.15 H (109K ohms) with halves joined or 44.0 H (290K ohms) in series, with leakage inductance of 15.64 mH and 63.50 mH.

The drawing describes a sealed case with an epoxy-potted transformer (the series sheet refers to a wax potted core). An electrostatic shield between primary and secondary is connected to the green lead. Humbucking construction and balanced split windings on both sides add circuit versatility, and the primary may be used as the secondary and vice versa for impedance matching.

The case is deep-drawn steel with a tin plated finish, sealed, and fitted with two 6-32 mounting studs; mounting hardware is included. Leads are a minimum of 4" long. The listed overall dimensions are A 1.20 in (30 mm), B 1.70 in (43 mm), C 1.65 in (42 mm) and D 1.32 in (34 mm). Drawing tolerances are ±0.063" on A, B and D, with C 1.65" max. The 850LA is RoHS and REACH compliant, with a listed shipping weight of 0.44 lbs (0.20 kg) and UNSPSC 39121301.