Hammond 1750N 50W JMP/JCM 800 Output Transformer, 4/8/16 Ohm

The 1750N is a 50 watt push-pull output transformer for tube guitar amplifiers, designed as a drop-in replacement for original units such as those in the Marshall JMP and JCM 800 (the drawing references P-TM050). Amp model names are listed by the manufacturer for reference only, and it states it is not affiliated with the amplifier companies.

Its 3,200 ohm centre-tapped primary serves 4, 8 and 16 ohm secondary taps. Typical DC resistance is 41.74 ohms blue-white and 43.14 ohms white-red on the primary, and 0.770 ohm black-yellow on the secondary. At 1.0 kHz, 1.0 V open circuit, the blue-red primary measures 18.3 H (112K ohm), and primary leakage inductance is 13.41 mH.

The drawing notes list a frequency response of 70 Hz to 15 kHz (0/-1 dB reference @ 1 kHz) and distortion under 1% at 70 Hz; the unit label reads 50 Hz - 12 kHz. It is bobbin wound, with materials and design specifications kept as close as possible to the original to preserve the stock tone.

The open-style frame has 11 in minimum leads stripped 0.5 in: blue and red primary with white centre tap, black common, yellow 4 ohm, orange 8 ohm and violet 16 ohm. Drawing dimensions are A 3.125 in, B 3.350 in max, C 3.800 in max, D 2.500 in and E 2.450 in, with G 0.188 x 0.406 in. Ratings are 1500 VRMS and -40 to 105 degC. It is RoHS and REACH compliant and ships at 4 lbs (1.81 kg).