1750L Hammond PP Übertrager Bassman 125A13A 022871

Hammond 1750L – 60 W output transformer for Bassman and related Fender stages

The Hammond 1750L is a paper-wound push-pull output transformer with a 4.2 kΩ plate-to-plate primary and a fixed 4 Ω loudspeaker output. Hammond documents it for several Bassman, Hot Rod DeVille and Concert II versions.

Fender references 125A13A and 022871 are explicitly assigned. The transformer is rated at 60 W and can serve as a replacement or as the basis of a correctly designed push-pull output stage.

Suitable applications

• Fender Bassman amplifiers using reference 125A13A or 022871
• Documented Blackface and Silverface Bassman chassis
• Hot Rod DeVille and Concert II amplifiers with a matching version
• Push-pull stages using two 6L6, 6L6GC or 5881 valves
• Guitar amplifiers requiring approximately 4.2 kΩ and a 4 Ω total load
• New amplifiers in the 60 W transformer class following a complete load-line calculation

Technical data

Product type

Push-pull guitar-amplifier output transformer

Model

Hammond 1750L

Documented amplifier families

Bassman, Hot Rod DeVille and Concert II

Documented Fender references

125A13A and 022871

Documented chassis families

Including 5F6, 5F6A, AA864, AA165, AB165 and AA270

Primary impedance

4.2 kΩ plate-to-plate with centre tap

Secondary impedance

4 Ω

Transformer power rating

60 W

Amplifier topology

Push pull

Typical output-valve complement

Two 6L6, 6L6GC or 5881 valves in total at a suitable operating point

Winding type

Paper winding

Primary inductance

Approx. 6.52 H at 1 kHz, 1 V and open secondary

Primary DC resistance

Approx. 98.6 Ω between brown and blue

Secondary DC resistance

Approx. 0.170 Ω between black and green

Primary leakage inductance

Approx. 4.93 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 2% 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. 102.9 × 77.5 × 87.9 mm maximum

Mounting dimensions

Approx. 88.9 × 63.2 mm

Mounting slots

Approx. 4.75 × 7.62 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 circuit of the exact amplifier version where global feedback is used

Fixed 4 Ω design

The nominal 4.2 kΩ plate-to-plate load is obtained with a total loudspeaker load of 4 Ω. A different loudspeaker impedance changes the load reflected to the output valves proportionally.

An 8 Ω loudspeaker would ideally reflect approximately 8.4 kΩ. This substantial mismatch should not be used merely because the loudspeaker can be connected electrically.

Comparison with the Hammond 1750M

The Hammond 1750L has a fixed 4 Ω output and is explicitly associated with 125A13A and 022871. The Hammond 1750M instead provides 2, 4 and 8 Ω taps and is assigned to additional DeVille, Concert and Super Concert versions.

Both models provide 4.2 kΩ and a 60 W rating, but their different mechanics, secondary windings and equipment assignments mean that they are not automatically interchangeable.

Safety notes

Lethal plate and signal voltages are present on the primary. Install the open transformer with complete touch protection and adequate mechanical support, and fully discharge the amplifier before service work.

Questions about selection and use

Which output transformer suits a Fender Bassman using 125A13A or 022871?

Hammond 1750L is intended for documented Bassman applications using references 125A13A and 022871 and provides 4.2 kΩ plate-to-plate, a fixed 4 Ω output and a 60 W rating.

Which 60 W push-pull output transformer suits two 6L6 or 5881 valves with 4.2 kΩ and 4 Ω?

Hammond 1750L is a suitable starting point for a correctly designed two-6L6 or 5881 stage requiring approximately 4.2 kΩ plate-to-plate and a total loudspeaker load of 4 Ω.

Can the Hammond 1750L be used in a Hot Rod DeVille or Concert II?

Yes, the Hammond 1750L can be used in a Hammond-documented Hot Rod DeVille or Concert II version when the reference, 4 Ω load, mounting and lead arrangement correspond to the particular amplifier.

Is the Hammond 1750M a suitable alternative when 2, 4 and 8 Ω are required?

Yes, the Hammond 1750M provides 2, 4 and 8 Ω taps with the same nominal 4.2 kΩ primary; the amplifier version, mechanics, winding type and feedback phase still require separate verification.