1750NA Hammond 30W Übertrager JTM30 JTM60 292-772 Marshall

Hammond 1750NA – pin-mounted 30 W output transformer for JTM30 and JTM60

The Hammond 1750NA is a pin-mounted push-pull output transformer providing 6 kΩ plate-to-plate and secondary connections for 8 and 16 Ω. Hammond names Drake 292-772 as the comparison reference.

The product page and individual drawing assign it to JTM30 and JTM60 applications. Because of the 30 W rating and differing amplifier versions, any JTM60 installation requires particularly careful verification.

Suitable applications

• Marshall JTM30 amplifiers with a matching transformer and pin layout
• Replacement applications for Drake 292-772
• JTM60 amplifiers only where the exact transformer and equipment version is confirmed
• Push-pull stages requiring approximately 6 kΩ
• Total loudspeaker loads of 8 or 16 Ω
• Pin-mounted new builds in the 30 W transformer class

Technical data

Product type

Pin-mounted push-pull guitar-amplifier output transformer

Model

Hammond 1750NA

Documented amplifier families

JTM30 and, on the product page and individual drawing, JTM60

Hammond comparison reference

Drake 292-772

Primary impedance

6 kΩ plate-to-plate with centre tap

Secondary impedances

8 and 16 Ω

Transformer power rating

30 W

Amplifier topology

Push pull

Output-valve complement

Amplifier- and revision-dependent; do not infer it from the model name alone

Winding type

Bobbin winding

Primary inductance

Approx. 8.00 H at 1 kHz, 1 V and open secondary

Secondary inductance at 8 Ω

Approx. 37.8 mH

Secondary inductance at 16 Ω

Approx. 76.64 mH

Primary DC resistance

Approx. 147.36 Ω between pins 18 and 14

Secondary DC resistance at 8 Ω

Approx. 0.580 Ω between pins 12 and 10

Secondary DC resistance at 16 Ω

Approx. 0.820 Ω between pins 12 and 8

Primary leakage inductance

Approx. 10.26 mH at 1 kHz, 1 V and short-circuited secondary

Specified frequency response

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

Additional component marking

50 Hz to 12 kHz, without a separate second tolerance statement

Distortion

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

Dielectric test

2,500 V RMS

Temperature range

-40 to +105 °C

Connection type

Chassis- or pin-mounted construction

Dimensions

Approx. 76.2 × 63.5 × 62.6 mm

Mounting dimensions

Approx. 40.6 × 50.8 mm, with further dimensions shown in the manufacturer drawing

Hammond shipping weight

Approx. 0.91 kg

Pin connections

Pin 18

First primary connection to one output-valve plate

Pin 17

Primary centre tap to B+

Pin 14

Second primary connection to the opposite output-valve plate

Pin 12

Secondary common

Pin 10

8 Ω loudspeaker connection

Pin 8

16 Ω loudspeaker connection

View

Compare all pin numbers with the underside view in the manufacturer drawing

JTM30 and JTM60 assignment

The current Hammond series list explicitly assigns the 1750NA to the JTM30. The JTM60 assignment appears on the product page and individual drawing but not in the current series list.

A JTM60 repair must therefore confirm the original Drake 292-772 reference, power class, pin layout, primary load and loudspeaker connections of the particular amplifier.

Selecting the loudspeaker impedance

Use pin 10 for an 8 Ω total load and pin 8 for a 16 Ω total load. The other output remains unloaded and is safely isolated according to the equipment wiring.

Safety notes

Lethal plate and signal voltages are present on the primary pins. Installation requires adequate electrical clearances, and the equipment must be fully discharged before service work.

Questions about selection and use

Which output transformer suits a Marshall JTM30 using Drake 292-772?

Hammond 1750NA is documented for the JTM30 and Drake 292-772 comparison reference and provides 6 kΩ plate-to-plate, 8/16 Ω outputs and a 30 W rating.

Which pin-mounted 30 W output transformer provides 6 kΩ with 8 and 16 Ω outputs?

Hammond 1750NA combines a pin-mounted construction with a 6 kΩ plate-to-plate primary and separate 8 and 16 Ω secondary connections.

Can the Hammond 1750NA be used in a JTM60?

Yes, the Hammond 1750NA can be used in a JTM60 version covered by the product page and individual drawing when the Drake reference, pin layout, 30 W transformer class and electrical data match the particular amplifier.

Is the Hammond 1750NA suitable for a newly designed 30 W push-pull amplifier?

Yes, the Hammond 1750NA can be used in a new amplifier when the 6 kΩ load, 8 or 16 Ω speaker impedance, output-valve complement, plate voltage and quiescent currents suit the circuit.