1750J Hammond PP Übertrager Pro Reverb 125A6A Fender

Hammond 1750J – 40 W output transformer with 4 kΩ to 4 Ω

The Hammond 1750J is a push-pull output transformer with a 4 kΩ plate-to-plate primary and a fixed 4 Ω loudspeaker output. Hammond documents it for several historical Bandmaster, Tremolux, Pro and Pro Reverb circuits.

References 125A6A, 022848 and 125A7A are explicitly assigned in the current Hammond selection list. The transformer uses a bobbin winding and carries a 40 W rating.

Suitable applications

• Fender Pro and Pro Reverb amplifiers with a matching reference and circuit
• Fender Bandmaster and Tremolux amplifiers using the documented 4 Ω load
• Replacement applications for 125A6A, 022848 or 125A7A
• Push-pull output stages requiring approximately 4 kΩ
• Correctly designed two-6L6 or 5881 output stages
• Guitar amplifiers with a fixed total loudspeaker load of 4 Ω

Technical data

Product type

Push-pull guitar-amplifier output transformer

Model

Hammond 1750J

Documented amplifier families

Bandmaster, Tremolux, Pro and Pro Reverb

Documented references

125A6A, 022848 and 125A7A

Documented chassis families

Including Blonde 6G7-A, Blackface AA763/AB763 and several historical Reverb versions

Primary impedance

4 kΩ plate-to-plate with centre tap

Secondary impedance

4 Ω

Transformer power rating

40 W

Amplifier topology

Push pull

Winding type

Bobbin winding

Primary inductance

Approx. 19.8 H at 1 kHz, 1 V and open secondary

Primary DC resistance

Approx. 185 Ω between brown and blue

Secondary DC resistance

Approx. 0.400 Ω

Primary leakage inductance

Approx. 227.3 mH at 1 kHz, 1 V and short-circuited secondary

Frequency response

70 Hz to 15 kHz, 0/-1.5 dB referenced to 1 kHz

Distortion

Less than 3% 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 229 mm or 9 inches

Dimensions

Approx. 101.6 × 71.1 × 66.8 mm maximum

Mounting centres

Approx. 90.4 mm

Mounting-hole diameter

Approx. 4.75 mm

Hammond shipping weight

Approx. 1.81 kg

Manufacturing note

Made in Canada according to the current component drawing

Lead connections

Brown

First primary connection to one output-valve plate

Red

Primary centre tap to B+

Blue

Second primary connection to the opposite output-valve plate

Black

Secondary common or loudspeaker ground

Green

4 Ω loudspeaker connection

Phase

Follow the applicable original circuit exactly where feedback is used

Historical and current model names

Select the Hammond 1750J by reference, plate-to-plate load and 4 Ω total speaker impedance. An identical or similar model name on a later amplifier does not establish electrical or mechanical compatibility.

The total loudspeaker impedance is particularly important. The fixed 4 Ω output is not intended for a nominal 8 Ω cabinet unless the resulting primary load is deliberately required by a redesigned output stage.

Comparison with the Hammond 1760J

The Hammond 1750J has a fixed 4 Ω output. The Hammond 1760J uses the same basic 4 kΩ and 40 W specification but adds 4, 8 and 16 Ω taps.

Safety notes

Lethal plate voltage is present on the primary. Install the transformer in a closed, touch-safe enclosure and fully discharge the output stage before service work.

Questions about selection and use

Which output transformer suits a Pro, Pro Reverb, Bandmaster or Tremolux using 125A6A, 022848 or 125A7A?

Hammond 1750J is designed for these documented Fender applications and provides 4 kΩ plate-to-plate, a fixed 4 Ω output, a 40 W rating and bobbin winding.

Which 40 W push-pull output transformer suits a 6L6 stage requiring 4 kΩ plate-to-plate and 4 Ω?

Hammond 1750J is a suitable starting point for a correctly designed two-6L6 or 5881 output stage requiring approximately 4 kΩ plate-to-plate and a nominal total load of 4 Ω.

Can the Hammond 1750J be used in a newly designed 6L6 push-pull amplifier?

Yes, the Hammond 1750J can be used in a new amplifier when the 4 kΩ load, 4 Ω output, 40 W rating, valve count, plate and screen voltage and quiescent currents suit the circuit.

Is the Hammond 1760J a suitable alternative for 4, 8 and 16 Ω loudspeakers?

Yes, the Hammond 1760J provides documented 4, 8 and 16 Ω secondary taps, while the Hammond 1750J is fixed at 4 Ω.