290FEX Hammond Netztrafo Twin Reverb / Bassman Repl.

Hammond 290FEX – 240 V power transformer for Twin Reverb, Bassman 100 and 125P34A / 022756

The Hammond 290FEX is a paper-wound power transformer for high-powered valve guitar amplifiers. Its single primary winding is rated for 240 V at 50/60 Hz. The secondary windings provide 320-0-320 V at 518 mA, a 60 V bias tap and a separate 6.5 V heater supply rated at 5.5 A.

Hammond lists the 290FEX as the international power-transformer version for Twin Reverb, Twin Reverb 100, Bassman 100 and related Showman or 100-watt applications. Fender references 125P34A and 022756 are documented for the 290FEX, while Hammond’s dedicated Twin Reverb 100 page also lists 125P34AX. These numbers support part identification but do not replace verification of the circuit, mains voltage, mounting and lead arrangement.

Suitable applications

• Twin Reverb and Twin Reverb 100 versions listed by Hammond, including AA270, AA769, AB763, AC568, Blackface and Silverface applications
• Bassman 100 amplifiers associated with Fender references 125P34A and 022756
• Showman, Showman Reverb, Showman Dual or Dual Showman, and Showman Dual Reverb circuits with matching requirements
• Quad Reverb 100, Super Six Reverb 100 and other 100-watt applications listed by Hammond
• New builds requiring a 240 V primary, 320-0-320 V high-voltage supply and up to 5.5 A of heater current

Technical data

Product type

Power transformer for valve guitar amplifiers

Manufacturer application references

Twin Reverb, Twin Reverb 100, Bassman 100, Showman, Dual Showman and related 100-watt applications according to Hammond

Fender reference numbers

125P34A and 022756; Hammond additionally lists 125P34AX on its Twin Reverb 100 application page

Winding construction

Paper wound with an external flux band

Primary winding

One 240 V winding for 50/60 Hz; no separate 220 or 230 V primary tap

High-voltage winding

640 V CT, equivalent to 320-0-320 V, at 517.5 mA in the drawing and rounded to 518 mA on the current product page

Bias supply

60 V tap on one half of the high-voltage winding

Heater winding

6.5 V at 5.5 A between the two green flying leads

Heater centre tap

No accessible centre tap is shown in the Hammond connection diagram

Separate 5 V winding

Not provided; the 290FEX has no separate heater supply for a tube rectifier

No-load voltages

665.26 V CT from the high-voltage winding and 7.02 V from the heater winding at 240 V and 50 Hz

Turns ratio

1:2.77 from the primary winding to the complete red-to-red high-voltage winding

Exciting current

255 mA maximum at 240 V and 50 Hz

Primary DC resistance

3.161 Ω between white and black, ±20% at 20 °C

High-voltage winding DC resistance

20.19 Ω between red and red, ±20% at 20 °C

Heater winding DC resistance

0.074 Ω between green and green, ±20% at 20 °C

Electrostatic screen

Internal screen between the primary and secondary windings with an orange flying lead

Dimensions

Approx. 95.3 × 119.1 × 114.3 mm according to Hammond drawing dimensions A × B × C

Mounting

Open-frame chassis mounting with four threaded studs; compare the mounting pattern and available clearance before drilling

Flying leads

At least 9 in or approx. 229 mm long and stripped by approx. 12.7 mm at the ends

Shipping weight

Approx. 5.28 kg according to Hammond

Connection details

240 V primary winding

Black–white; apply the mains supply between the black and white leads

Electrostatic screen

Orange; connect according to the amplifier’s verified grounding arrangement. The orange lead does not replace the protective-earth conductor

High-voltage winding

Red and red are the two 320 V ends; red/yellow is the centre tap and the connection marked 0 V in the Hammond diagram

Bias tap

Red/blue provides 60 V AC relative to the red/yellow centre tap

6.5 V heater winding

Green–green, rated 6.5 V at a maximum of 5.5 A; no separate centre tap is brought out

Comparison with related Hammond models

Hammond 290FEX

International 240 V version for 50/60 Hz with 640 V CT at 518 mA, a 60 V bias tap and 6.5 V at 5.5 A

Hammond 290FX

120 V version for 60 Hz with the same documented secondary ratings, amplifier applications and Fender reference numbers

Hammond 290EEBZ

Separate model for the ’65 Twin Reverb Reissue with a multi-voltage primary and different secondary windings; it is not electrically identical to the 290FEX

Selection and installation notes

The specified 320-0-320 V, 60 V and 6.5 V figures are rated values at the intended load. The high-voltage and heater readings are higher at no load. Final operating voltages also depend on the actual mains voltage, rectifier circuit, filtering and total amplifier current demand.

The 290FEX has a single 240 V primary winding. Ideal proportional scaling at exactly 230 V gives approximately 307-0-307 V, 57.5 V at the bias tap and 6.23 V at the heater winding. These figures are calculated estimates and must be checked under normal operating load in the completed amplifier.

The connection diagram shows no accessible heater centre tap. An artificial heater reference, hum-balance arrangement or the amplifier’s existing reference circuit must therefore follow the exact schematic. The transformer also provides no separate 5 V winding for a tube rectifier.

Reference numbers alone do not guarantee mechanical or electrical compatibility with every amplifier revision. The ’65 Twin Reverb Reissue, later Twin versions and amplifiers using different rectifier arrangements require the specific transformer assigned by Hammond.

Mains wiring, primary fusing, protective earth, strain relief, touch protection and insulation clearances must be completed by a qualified technician. Protective earth must be bonded separately and permanently to the metal chassis, independently of the orange screen lead. Filter capacitors can retain lethal voltages after the amplifier has been disconnected.

Questions about selection and use

Is the Hammond 290FEX suitable for Twin Reverb and Bassman 100 amplifiers associated with Fender references 125P34A or 022756?

Yes, Hammond explicitly lists the 290FEX as the international 240 V version for Twin Reverb and Bassman 100 applications associated with Fender references 125P34A and 022756. Hammond also lists 125P34AX for Twin Reverb 100; the circuit, chassis and lead arrangement must still match.

Can the Hammond 290FEX be operated from a European 230 V mains supply?

Yes, its single primary winding is nominally rated for 240 V and can be operated from 230 V when the slightly lower secondary voltages suit the circuit. Ideal proportional scaling at exactly 230 V gives approximately 307-0-307 V, 57.5 V at the bias tap and 6.23 V at the heater winding; verify the actual values under load.

Is the Hammond 290FEX suitable as the 240 V alternative to the Hammond 290FX?

Yes, the 290FEX and 290FX have the same documented secondary ratings and application references. The 290FX is intended for 120 V at 60 Hz, while the 290FEX is intended for 240 V at 50/60 Hz; confirm the dimensions and wiring of the delivered transformer before installation.