1760K Hammond 50W Übertrager Bassman Super Reverb 125A9A

Hammond 1760K – 50 W output transformer with 2, 4 and 8 Ω taps

The Hammond 1760K is a paper-wound push-pull output transformer providing 4 kΩ plate-to-plate and secondary taps for 2, 4 and 8 Ω. Hammond lists it for compatible Bassman, Super and Super Reverb circuits.

The principal references are 125A9A and 022855. The transformer supports output stages requiring a total loudspeaker impedance of 2, 4 or 8 Ω.

Suitable applications

• Fender Bassman amplifiers using a suitable 4 kΩ output stage
• Fender Super and Super Reverb amplifiers with a compatible chassis version
• Replacement applications for 125A9A or 022855
• Push-pull output stages using two 6L6, 6L6GC or 5881 valves
• Multiple-speaker systems totalling 2, 4 or 8 Ω
• New amplifiers in the 50 W transformer class

Technical data

Product type

Push-pull guitar-amplifier output transformer

Model

Hammond 1760K

Documented amplifier families

Bassman, Super and Super Reverb

Documented principal references

125A9A and 022855

Additional numbers on the Hammond Super application page

45249 and 036485; verify the exact amplifier version before installation

Primary impedance

4 kΩ plate-to-plate with centre tap

Secondary impedances

2, 4 and 8 Ω

Transformer power rating

50 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. 5.38 H at 1 kHz, 1 V and open secondary

Primary DC resistance

Approx. 89.43 Ω between brown and blue

Secondary DC resistance at 2 Ω

Approx. 0.091 Ω between black and white

Secondary DC resistance at 4 Ω

Approx. 0.183 Ω between black and yellow

Secondary DC resistance at 8 Ω

Approx. 0.219 Ω between black and green

Secondary inductance at 2 Ω

Approx. 8.53 mH at 1 kHz and 1 V

Secondary inductance at 4 Ω

Approx. 17.59 mH at 1 kHz and 1 V

Secondary inductance at 8 Ω

Approx. 33.62 mH at 1 kHz and 1 V

Primary leakage inductance

Approx. 3.136 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 × 82.2 × 88.5 mm

Mounting dimensions

Approx. 88.9 × 65.0 mm

Mounting slots

Approx. 4.5 × 7.6 mm

Hammond shipping weight

Approx. 1.81 kg

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 tap

Yellow

4 Ω loudspeaker tap

Green

8 Ω loudspeaker tap

Multiple speakers and total impedance

The total impedance of all connected loudspeakers is decisive. Four nominal 8 Ω speakers connected fully in parallel ideally provide a 2 Ω load.

Use the tap corresponding to this total impedance and insulate the two unused secondary leads separately.

Transformer rating and amplifier output

The 50 W figure describes the transformer's rating. A documented Super Reverb version can have a different complete-amplifier output rating.

Comparison with the Hammond 1750K

The Hammond 1750K has a fixed 2 Ω output. The Hammond 1760K uses the same nominal primary load and power class but adds 4 and 8 Ω taps.

Safety notes

Lethal plate and signal voltages are present on the primary. Install the transformer with complete touch protection and adequate mechanical support.

Questions about selection and use

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

Hammond 1760K is intended for these documented Fender applications and provides 4 kΩ plate-to-plate, 2/4/8 Ω taps, paper winding and a 50 W rating.

Which 50 W output transformer suits two 6L6 valves requiring 4 kΩ with a 2, 4 or 8 Ω loudspeaker load?

Hammond 1760K is a suitable starting point for a correctly designed two-6L6 or 5881 output stage requiring 4 kΩ plate-to-plate and a total load of 2, 4 or 8 Ω.

Can the Hammond 1760K be configured for 2, 4 or 8 Ω?

Yes, the Hammond 1760K has separate secondary taps for 2, 4 and 8 Ω. Use only the tap corresponding to the actual total loudspeaker impedance.

Is the Hammond 1760K a suitable alternative to the Hammond 1750K?

Yes, the Hammond 1760K can replace the 1750K in a compatible circuit and adds 4 and 8 Ω taps to the fixed 2 Ω output of the 1750K.