Hammond 1750NA 30W Marshall JTM30/JTM60 Output Transformer, 8/16 Ohm

The 1750NA is a 30 watt push-pull output transformer for tube guitar amplifiers, designed as a drop-in replacement for original units such as those in the Marshall JTM30 and JTM60, and similar to OEM part Drake 292-772 (reference only). The manufacturer notes that amp model names are trademarks listed for reference and that it is not affiliated with the amplifier companies.

Unlike the lead-wire units in the series, the 1750NA connects through numbered pins. The 6,000 ohm primary runs between pins 18 and 14 with pin 17 as the centre tap; the secondary common is pin 12, with 8 ohm on pin 10 and 16 ohm on pin 8. Typical DC resistance is 147.36 ohms on the primary, 0.580 ohm (12-10) and 0.820 ohm (12-8) on the secondaries.

At 1.0 kHz, 1.0 V open circuit, the primary measures 8.00 H (49.78K ohm), and the 8 and 16 ohm secondaries 37.8 mH (410.3 ohm) and 76.64 mH (716.6 ohm). Primary leakage inductance is 10.26 mH. The drawing notes give 70 Hz to 15 kHz (0/-1 dB reference @ 1 kHz) and distortion under 1% at 70 Hz; the label reads 50 Hz - 12 kHz.

Dielectric strength is 2500 VRMS and the temperature range -40 to 105 degC. The bobbin-wound unit was built with materials kept as close as possible to the original to preserve the stock tone. Drawing dimensions are A 3.000 in, B 2.500 in, C 2.465 in, D 1.600 in, E 0.300 in, G 0.219 in, H 2.500 in and J 2.000 in. It is RoHS and REACH compliant and ships at 2 lbs (0.91 kg).