Hammond 1750J 40W Pro Reverb Output Transformer, 4 Ohm

The 1750J is a 40 watt push-pull output transformer for tube guitar amplifiers, designed as a drop-in replacement for the original unit in the Fender Bandmaster, Tremolux and Pro. It is listed as similar to Fender part numbers 125A6A, 022848 and 125A7A, and the reference chassis list spans Blonde 6G7-A, Blackface AA763 and AB763, Silverface AC568 and AD1269, and Reverb variants including AA763, AA1069 and AA270.

It pairs a 4,000 ohm centre-tapped primary with a single 4 ohm secondary. Typical DC resistance is 185.0 ohms brown-blue on the primary and 0.400 ohm black-green on the secondary. Primary inductance is 19.8 H (120K ohm) at 1.0 kHz, 1.0 V open circuit, and primary leakage inductance is 227.3 mH.

The drawing lists a frequency response of 70 Hz to 15 kHz (0/-1.5 dB reference @ 1 kHz) and distortion of less than 3% at 70 Hz. The unit is bobbin wound, with materials and design specifications kept as close as possible to the original part to preserve the stock tone.

Open-style construction provides 9 in minimum leads: brown and blue primary with red centre tap, black common and green 4 ohm. Drawing dimensions are A 4.000 in, B 2.800 in reference, C 2.63 in max and D 3.560 in. Ratings are 1500 VRMS dielectric strength and -40 to 105 degC. It is RoHS and REACH compliant and ships at 4 lbs (1.81 kg).