1750C Hammond SE Übertrager Fender 125A35A 022905 Ersatz

Hammond 1750C – 5/8 kΩ SE output transformer for Champ and Vibro Champ

The Hammond 1750C is a single-ended output transformer for classic small Fender valve amplifiers. A primary tap provides a choice of approximately 5 or 8 kΩ, while the secondary is fixed at 3.2 Ω.

Hammond documents the 1750C for Champ, Vibro Champ, Bronco, Harvard and Princeton amplifiers together with references 125A35A, 022905 and 125A3A. A single 6V6 with a correctly calculated operating point is a typical application.

Suitable applications

• Fender Champ 5C1, 5E1 and 5F1 amplifiers
• Fender Vibro Champ AA764 and related Blackface or Silverface circuits
• Fender Bronco, Harvard and Tweed Princeton applications
• Replacement for 125A35A, 022905 and 125A3A where the circuit matches
• Single-ended 6V6 stages requiring approximately 5 or 8 kΩ
• Compact guitar-amplifier projects using a nominal 3.2 Ω speaker load

Technical data

Product type

Single-ended guitar-amplifier output transformer

Model

Hammond 1750C

Documented references

125A35A, 022905 and 125A3A

Documented amplifier families

Champ, Vibro Champ, Bronco, Harvard and Princeton

Primary impedances

Approx. 5 or 8 kΩ

Secondary impedance

3.2 Ω

Transformer power rating

5 W

Maximum primary DC

50 mA; a transformer limit rather than a universal target for every 6V6 circuit

Primary inductance at 5 kΩ

Approx. 14.25 H at 1 kHz, 1 V and open secondary

Primary inductance at 8 kΩ

Approx. 20.42 H at 1 kHz, 1 V and open secondary

Secondary inductance

Approx. 64.53 mH

Red-to-brown primary DC resistance

Approx. 255.84 Ω

Brown-to-blue primary DC resistance

Approx. 73.89 Ω

Total red-to-blue primary DC resistance

Approximately 329.73 Ω

Secondary DC resistance

Approx. 0.295 Ω

Leakage inductance at 5 kΩ

Approx. 54.28 mH

Leakage inductance at 8 kΩ

Approx. 74.48 mH

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

1,500 V RMS

Temperature range

-40 to +105 °C

Winding type

Bobbin winding

Lead length

At least approximately 229 mm or 9 inches

Dimensions

Approx. 71.5 × 39.6 × 42.7 mm

Mounting centres

Approx. 60.3 mm

Mounting-hole diameter

Approx. 4.75 mm

Hammond shipping weight

Approx. 0.29 kg

Manufacturing note

Made in Canada according to the current component drawing

Primary and secondary connections

Red

Marked primary winding start or B+ connection

Brown

5 kΩ primary tap to the valve plate

Blue

8 kΩ primary connection to the valve plate

Black

Marked secondary winding start or common connection

Yellow

3.2 Ω loudspeaker connection

Unused primary lead

Insulate securely when selecting one primary impedance

Reflected load with a 4 Ω loudspeaker

The 1750C has no separate 4 Ω tap. Connecting a 4 Ω loudspeaker instead of 3.2 Ω increases the reflected primary load ideally by a factor of 1.25.

The 5 kΩ connection then becomes approximately 6.25 kΩ, while the 8 kΩ connection becomes approximately 10 kΩ. Use this only when the resulting load deliberately suits the valve load line.

Comparison with the 1760C and 1760CP

Hammond 1750C

Bobbin winding with a fixed 3.2 Ω output

Hammond 1760C

Bobbin winding with 3.2, 8 and 16 Ω secondary connections

Hammond 1760CP

Paper winding with 4 and 8 Ω secondary connections

Selection and safety notes

Select the primary load from plate voltage, quiescent current, valve type, loudspeaker load and operating mode. The 6V6 designation alone is insufficient to choose between 5 and 8 kΩ.

Lethal plate voltage can be present on the open transformer. Insulate unused primary leads and install the transformer with complete touch protection.

Questions about selection and use

Which output transformer suits a Fender Champ or Vibro Champ using 125A35A or 022905?

Hammond 1750C is documented for Champ and Vibro Champ applications together with references 125A35A, 022905 and 125A3A, providing 5 or 8 kΩ to a 3.2 Ω secondary.

Which Hammond SE output transformer provides 5 or 8 kΩ for a single 6V6?

Hammond 1750C provides both primary loads through a tap and is a suitable starting point for a correctly designed 6V6 SE stage operating at up to 50 mA with an appropriate loudspeaker load.

Can the Hammond 1750C operate with a 4 Ω loudspeaker?

Yes, the Hammond 1750C can operate with a 4 Ω loudspeaker, but it then reflects approximately 6.25 kΩ in the 5 kΩ connection or 10 kΩ in the 8 kΩ connection.

Is the Hammond 1750C suitable for original 3.2 Ω Champ circuits?

Yes, the Hammond 1750C is specifically documented for corresponding Champ, Vibro Champ and related original circuits through its fixed 3.2 Ω secondary.