1750K Hammond PP Übertrager Fender Super Rev 125A9A 022855

Hammond 1750K – 50 W output transformer with 4 kΩ to 2 Ω

The Hammond 1750K is a paper-wound push-pull output transformer with a 4 kΩ plate-to-plate primary and a fixed 2 Ω loudspeaker output. Hammond documents it for Bassman, Super and Super Reverb applications.

References 125A9A and 022855 are officially assigned. The complete impedance of the connected speaker system is decisive rather than the impedance of one individual loudspeaker.

Suitable applications

• Fender Super and Super Reverb amplifiers with a matching 2 Ω total load
• Documented Tweed Bassman circuits
• Replacement applications for 125A9A or 022855
• Push-pull output stages requiring approximately 4 kΩ
• Correctly designed two-6L6 or 5881 output stages
• Multiple-speaker systems providing a calculated total of 2 Ω

Technical data

Product type

Push-pull guitar-amplifier output transformer

Model

Hammond 1750K

Documented amplifier families

Bassman, Super and Super Reverb

Documented references

125A9A and 022855

Primary impedance

4 kΩ plate-to-plate with centre tap

Secondary impedance

2 Ω

Transformer power rating

50 W

Amplifier topology

Push pull

Typical output-valve complement

Two 6L6 or 5881 valves in total at a suitable operating point

Winding type

Paper winding

Primary inductance

Approx. 12.5 H at 1 kHz, 1 V and open secondary

Primary DC resistance

Approx. 89.43 Ω between brown and blue

Secondary DC resistance

Approx. 0.180 Ω

Primary leakage inductance

Approx. 3.34 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

2,000 V RMS

Temperature range

-40 to +105 °C

Lead length

At least approximately 229 mm or 9 inches

Dimensions

Approx. 103.2 × 79.4 × 87.7 mm

Mounting dimensions

Approx. 88.9 × 50.8 × 65.0 mm according to the manufacturer drawing

Mounting slots

Approx. 4.5 × 7.6 mm

Hammond shipping weight

Approx. 1.81 kg

Manufacturing note

Made in Canada according to the current component drawing

Lead connections

Blue

First primary connection to one output-valve plate

Red

Primary centre tap to B+

Brown

Second primary connection to the opposite output-valve plate

Black

Secondary common or loudspeaker ground

White

2 Ω loudspeaker connection

Phase

Follow the particular Fender circuit where global feedback is used

Calculating the total loudspeaker load

Multiple speakers must be connected so that their resulting impedance is approximately 2 Ω. Four nominal 8 Ω speakers connected fully in parallel provide an ideal total load of 2 Ω.

Connecting one 8 Ω speaker to the 2 Ω output would ideally quadruple the reflected primary impedance. This substantial mismatch is not a normal substitute for the correct secondary tap.

Comparison with the 1750KA and 1760K

Hammond 1750K

4 kΩ plate-to-plate, fixed 2 Ω output and references 125A9A or 022855

Hammond 1750KA

4.15 kΩ plate-to-plate, fixed 2 Ω output and additional documented 036485 applications

Hammond 1760K

4 kΩ plate-to-plate with 2, 4 and 8 Ω secondary taps

Safety notes

Lethal plate voltage is present on the primary. Install the heavy open transformer with complete touch protection and adequate mechanical support.

Questions about selection and use

Which output transformer suits a Super Reverb or Tweed Bassman using 125A9A or 022855?

Hammond 1750K is intended for these documented applications and provides 4 kΩ plate-to-plate, a fixed 2 Ω output, paper winding and a 50 W rating.

Which 50 W push-pull output transformer suits two 6L6 or 5881 valves with 4 kΩ plate-to-plate and 2 Ω?

Hammond 1750K is a suitable starting point for a correctly designed two-6L6 or 5881 output stage requiring approximately 4 kΩ plate-to-plate and a total loudspeaker load of 2 Ω.

Can the Hammond 1750K operate with a multiple-speaker system totalling 2 Ω?

Yes, the Hammond 1750K can operate with a correctly connected total load of 2 Ω. Calculate the impedances and the series or parallel connection of every loudspeaker first.

Is the Hammond 1760K a suitable alternative when 2, 4 and 8 Ω are required?

Yes, the Hammond 1760K provides documented 2, 4 and 8 Ω taps, while the Hammond 1750K has only a fixed 2 Ω output.