Hammond 1750K 50W Tweed Bassman Output Transformer, 2 Ohm

The 1750K is a 50 watt push-pull output transformer for tube guitar amplifiers, designed as a drop-in replacement for the original unit in the Fender Bassman and Super with the Tweed chassis. It is listed as similar to Fender part numbers 125A9A and 022855, a useful reference for restorers of tweed-era amplifiers.

It matches a 4,000 ohm centre-tapped primary to a 2 ohm secondary. Typical DC resistance is 89.43 ohms brown-blue on the primary and 0.180 ohm black-white on the secondary. At 1.0 kHz, 1.0 V open circuit, primary inductance is 12.5 H (81 KOhm), and leakage inductance (brown-blue) is 3.34 mH.

The drawing lists a frequency response of 70 Hz to 15 kHz (0/-1.0 dB reference @ 1 kHz) and distortion of less than 1% at 70 Hz. It is paper wound, with materials and design specifications kept as close as possible to the original part to preserve the stock tone, and constructed to look similar to the factory original where possible.

The open-style unit has 9.0 in minimum leads: blue and brown primary with red centre tap, black common and white 2 ohm secondary. Drawing dimensions are A 4.063 in, B 3.125 in, C 3.453 in, D 3.500 in, E 2.000 in and F 2.560 in, with G 0.177 x 0.300 in. Ratings are 2000 VRMS and -40 to 105 degC. It is RoHS and REACH compliant and ships at 4 lbs (1.81 kg).