1750N Hammond PP Übertrager JCM800 JMP 50W Marshall

Hammond 1750N – 50 W output transformer for Marshall JMP and JCM800

The Hammond 1750N is a bobbin-wound push-pull output transformer with a 3.2 kΩ plate-to-plate primary and secondary taps for 4, 8 and 16 Ω. Hammond documents it for Marshall JMP and JCM800 amplifiers.

The three loudspeaker taps provide flexible matching while retaining the nominal primary load. Verify the exact amplifier version, output-valve complement and mechanical fit before replacement.

Suitable applications

• Marshall JMP amplifiers with a corresponding 50 W output stage
• Marshall JCM800 amplifiers in a compatible chassis version
• Replacement applications around reference P-TM050
• Push-pull stages using two EL34 or 6CA7 valves
• Total loudspeaker loads of 4, 8 or 16 Ω
• New amplifiers using 3.2 kΩ in the 50 W transformer class

Technical data

Product type

Push-pull guitar-amplifier output transformer

Model

Hammond 1750N

Documented amplifier families

Marshall JMP and JCM800

Hammond comparison reference

P-TM050

Primary impedance

3.2 kΩ plate-to-plate with centre tap

Secondary impedances

4, 8 and 16 Ω

Transformer power rating

50 W

Amplifier topology

Push pull

Typical output-valve complement

Two EL34 or 6CA7 valves in total at a suitable operating point

Winding type

Bobbin winding

Primary inductance

Approx. 18.3 H at 1 kHz, 1 V and open secondary

Blue-to-white primary DC resistance

Approx. 41.74 Ω

White-to-red primary DC resistance

Approx. 43.14 Ω

Total blue-to-red primary DC resistance

Approximately 84.88 Ω

Secondary DC resistance at the 4 Ω tap

Approx. 0.770 Ω between black and yellow

Primary leakage inductance

Approx. 13.41 mH at 1 kHz, 1 V and short-circuited secondary

Frequency response

70 Hz to 15 kHz, 0/-1 dB referenced to 1 kHz

Distortion

Less than 1% at 70 Hz under the documented test conditions

Dielectric test

1,500 V RMS

Temperature range

-40 to +105 °C

Lead length

At least approximately 279 mm or 11 inches

Dimensions

Approx. 79.4 × 85.1 × 96.5 mm maximum

Mounting dimensions

Approx. 63.5 × 62.2 mm

Mounting slots

Approx. 4.78 × 10.31 mm

Hammond shipping weight

Approx. 1.81 kg

Lead connections

Blue

First primary connection to one output-valve plate

White

Primary centre tap to B+

Red

Second primary connection to the opposite output-valve plate

Black

Secondary common or loudspeaker ground

Yellow

4 Ω loudspeaker tap

Orange

8 Ω loudspeaker tap

Violet

16 Ω loudspeaker tap

Selection by Marshall amplifier version

The JMP and JCM800 names cover several circuit and chassis versions. Compare the primary load, valve count, mounting, lead routing and original output transformer before replacement.

Verify feedback phase after installation. Reversed primary connections can turn global negative feedback into positive feedback and cause severe oscillation.

Comparison with the Hammond 1750P

The Hammond 1750N is documented at 3.2 kΩ for JMP and JCM800 applications. The Hammond 1750P provides 3.4 kΩ, uses a pin-mounted construction and is assigned to the JCM900 in the current Hammond selection list.

Safety notes

Lethal plate and signal voltages may be present on the primary. Install the transformer with complete touch protection and fully discharge the amplifier before service work.

Questions about selection and use

Which output transformer suits a 50 W Marshall JMP or JCM800?

Hammond 1750N is intended for documented JMP and JCM800 applications and provides 3.2 kΩ plate-to-plate, 4/8/16 Ω taps and a 50 W rating.

Which 50 W push-pull output transformer suits two EL34 valves with 3.2 kΩ and several speaker impedances?

Hammond 1750N is a suitable starting point for a correctly designed two-EL34 or 6CA7 stage requiring 3.2 kΩ plate-to-plate and a total load of 4, 8 or 16 Ω.

Can the Hammond 1750N be configured for 4, 8 or 16 Ω?

Yes, the Hammond 1750N has separate secondary taps for 4, 8 and 16 Ω. The selected tap must match the actual total impedance of the connected loudspeakers.

Is the Hammond 1750N suitable for a newly designed EL34 push-pull amplifier?

Yes, the Hammond 1750N can be used in a new amplifier when the 3.2 kΩ load, 50 W rating, speaker impedance, plate and screen voltage and quiescent currents suit the circuit.