1750AX Hammond SE Übertrager Fender 125A12A Ersatz

Hammond 1750AX – SE reverb driver transformer for Fender 6G15 and 125A12A

The Hammond 1750AX is a single-ended reverb driver transformer for valve-powered spring-reverb circuits. Hammond documents it for the Fender Stand-Alone Reverb 6G15 and transformer reference 125A12A.

Its primary is rated at 7.5 kΩ, while the secondary feeds a nominal 8 Ω reverb-tank input. The 1750AX therefore belongs with a 6K6 or 6V6 power-valve driver rather than the common 12AT7 reverb circuit using a 25 kΩ transformer.

Suitable applications

• Repair and restoration of a Fender Stand-Alone Reverb 6G15
• Replacement for the documented 125A12A reference
• Single-ended reverb drivers using a 6K6 power valve
• 6V6 reverb drivers following the later 6G15 reissue concept
• New valve reverb circuits requiring a 7.5 kΩ primary and 8 Ω tank input
• Guitar-amplifier and studio DIY projects using a power-driven spring tank

Technical data

Product type

Single-ended reverb driver transformer

Model

Hammond 1750AX

Documented equipment application

Fender Stand-Alone Reverb 6G15

Documented reference number

125A12A

Primary impedance

7.5 kΩ

Secondary impedance

8 Ω

Transformer power rating

3.5 W

Maximum primary DC

50 mA; a transformer limit rather than a universal recommended valve operating point

Primary inductance

Approx. 6 H at 1 kHz, 1 V and open secondary

Secondary inductance

Approx. 11.72 mH at 1 kHz, 1 V and open primary

Primary DC resistance

Approx. 345 Ω

Secondary DC resistance

Approx. 0.699 Ω

Primary leakage inductance

Approx. 423 mH at 1 kHz with the secondary short-circuited

Frequency response

70 Hz to 15 kHz, 0/-3 dB referenced to 1 kHz

Distortion

Less than 1.5% 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. 60.5 × 41.9 × 35.6 mm

Mounting centres

Approx. 50.8 mm

Mounting-hole diameter

Approx. 4.75 mm

Hammond shipping weight

Approx. 0.18 kg

Manufacturing note

Made in Canada according to the current component drawing

Lead connections

Red

Marked primary winding start, normally connected to B+ as shown in the original circuit

Blue

Primary connection to the reverb-driver valve plate

Black

Marked secondary winding start or common connection

Green

8 Ω secondary connection to the spring-reverb tank input

Phase

Follow the applicable circuit diagram exactly where feedback is present

Difference from the Hammond 1750A

The 1750AX has a 7.5 kΩ primary and is intended for a power-capable 6K6 or 6V6 single-ended driver. The Hammond 1750A instead uses 25 kΩ to 8 Ω and belongs to the widely used 12AT7 or ECC81 reverb-driver circuit.

The 1750AX is also not a conventional loudspeaker output transformer. Its 8 Ω secondary is intended for the input of a compatible spring-reverb tank.

Selection and safety notes

Compare primary impedance, tank type, valve complement, plate current and mounting dimensions before replacement. The 8 Ω designation refers to the nominal tank-input impedance and must not be inferred solely from a DC-resistance measurement.

Lethal plate voltage is present on the primary. Install the open transformer with complete touch protection and adequate creepage and clearance distances.

Questions about selection and use

Which reverb driver transformer suits a Fender 6G15 chassis using the 125A12A reference?

Hammond 1750AX is documented for the Fender Stand-Alone Reverb 6G15 and reference 125A12A, providing a 7.5 kΩ primary, 8 Ω secondary and 3.5 W rating.

Which Hammond transformer suits a 6K6 or 6V6 spring-reverb driver requiring 7.5 kΩ?

Hammond 1750AX is a suitable starting point for a correctly designed 6K6 or 6V6 reverb driver using a 7.5 kΩ primary load, 8 Ω tank input and no more than 50 mA of primary DC.

Can the Hammond 1750AX drive an 8 Ω spring-reverb input?

Yes, the Hammond 1750AX has an 8 Ω secondary and can drive a compatible spring-reverb input when the driver valve, operating point and tank suit the 7.5 kΩ transformation.

Can the Hammond 1750AX be used in a newly designed valve reverb stage?

Yes, the Hammond 1750AX can be used in a newly designed SE reverb stage when 7.5 kΩ, 8 Ω, 3.5 W and the 50 mA maximum suit the circuit; the Hammond 1750A family is more appropriate for 12AT7 circuits requiring 25 kΩ.