290DEX Hammond Netztrafo Bassman 125P7D Replacement

Hammond 290DEX – 240 V Bassman power transformer for 5F6/5F6A and Fender 8087

The Hammond 290DEX is a bobbin-wound power transformer for valve guitar amplifiers. Its single primary winding is rated for 240 V at 50/60 Hz. The secondary windings provide 325-0-325 V at 230 mA, a 50 V bias tap, 6.3 V CT at 4 A and a separate 5 V winding at 3 A.

Hammond lists the 290DEX for lower-plate-voltage Bassman circuits, including Tweed, 5F6 and 5F6A builds and related combos. Hammond identifies Fender reference number 8087 for this model. Numbers 125P7D and 022798 are assigned to different Hammond power transformers in the current selection information and are therefore not used as 290DEX replacement references.

Suitable applications

• New builds and restoration of compatible Tweed Bassman circuits
• 5F6 and 5F6A amplifiers requiring the lower specified high-voltage secondary
• Service applications associated by Hammond with Fender reference number 8087
• Push-pull output stages using two 5881 or 6L6 power valves with compatible total current demand
• Valve amplifiers using a tube rectifier requiring no more than 3 A from a 5 V heater winding

Technical data

Product type

Power transformer for valve guitar amplifiers

Manufacturer application reference

Bassman “Lower Plate Volts”, Tweed, 5F6, 5F6A and related combos

Fender reference number

8087

Winding construction

Bobbin 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

650 V CT, equivalent to 325-0-325 V, at 230 mA

Bias supply

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

Valve-heater winding

6.3 V CT at 4 A

Rectifier-heater winding

Separate 5 V winding at 3 A

High-voltage no-load reading

709.4 V CT, equivalent to approximately 354.7-0-354.7 V, at 240 V and 50 Hz, each ±2% according to the production drawing

Bias-tap no-load reading

52.8 V relative to the red/yellow centre tap, ±2%

6.3 V winding no-load reading

6.72 V CT, equivalent to 3.36-0-3.36 V, ±2%

5 V winding no-load reading

5.28 V, ±2%

Exciting current

190 mA maximum at 240 V and 50 Hz

Primary DC resistance

5.059 Ω between the two black primary leads, ±20% at 20 °C

Secondary DC resistance

74.40 Ω red–red, 0.111 Ω yellow–yellow and 0.058 Ω green–green, each ±20% at 20 °C

Dielectric test

2,500 V AC between primary and secondary at 60 Hz for one second

Electrostatic screen

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

Dimensions

Approx. 87.3 × 103.2 × 104.8 mm according to drawing dimensions A × B × C

Mounting-related drawing dimensions

Dimension E approx. 69.9 mm and dimension F approx. 87.3 mm; compare the chassis and delivered transformer before drilling

Flying leads

At least 13 in or approx. 330 mm long and stripped by approx. 12.7 mm at the ends

Shipping weight

Approx. 3.63 kg according to Hammond

Connection details

240 V primary winding

Black–black; apply the mains supply across the two black leads

Electrostatic screen

Orange; connect according to the amplifier's verified grounding and chassis scheme. This lead does not replace the protective-earth conductor

High-voltage winding

Red and red are the two 325 V ends; red/yellow is the centre tap

Bias tap

Red/green provides 50 V AC relative to the red/yellow centre tap

5 V winding

Yellow–yellow, rated 5 V at a maximum of 3 A for the heater of a compatible tube rectifier

6.3 V heater winding

Green–green, rated 6.3 V at a maximum of 4 A; the two-colour green lead is the centre tap

Heater centre-tap documentation note

The current drawing labels the two-colour lead as green/yellow in the schematic but as green/white in the flying-lead illustration. Confirm its colour, continuity and equal half-winding voltages on the delivered transformer

Comparison with related Hammond models

Hammond 290DEX

240 V at 50/60 Hz, 650 V CT at 230 mA, 50 V bias, 6.3 V CT at 4 A and 5 V at 3 A; Hammond reference for Fender 8087

Hammond 290DX

Comparable secondary ratings and also associated with Fender 8087, but with a 120 V primary intended exclusively for 60 Hz

Hammond 290D2X / 290D2EX

710/610 V CT at 300 mA, 6.3 V CT at 5 A and 5 V at 3 A; Hammond lists references including 125P5D, 125P5DX, 022798 and 022806

Hammond 290EX / 290EEX

660 V CT at 275 mA, 53 V bias and 6.3 V CT at 4 A without a separate 5 V winding; Hammond lists 125P7D, 125P7DX, 022814 and 67233

Selection and installation notes

The specified 325-0-325 V, 6.3 V and 5 V figures are rated values at the intended load. No-load voltages are higher. The final B+ rail also depends on the actual mains voltage, rectifier, filter circuit and amplifier current demand.

The 290DEX has no dedicated 230 V primary tap. At exactly 230 V, ideal proportional scaling gives approximately 311-0-311 V, about 48 V at the bias tap, approximately 6.0 V CT and approximately 4.8 V. These are calculated estimates; heater, bias and high-voltage rails must be measured under normal operating load in the completed amplifier.

The complete 6.3 V load includes power valves, preamp valves, the pilot lamp and every other connected device. The 5 V winding may only supply rectifiers whose heater demand remains within its 3 A rating. The high-voltage current demand must also remain within the 230 mA design rating under all operating conditions.

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 290DEX suitable for a Bassman 5F6 or 5F6A build associated with Fender reference 8087?

Yes, Hammond lists the 290DEX for lower-plate-voltage Bassman circuits, Tweed, 5F6, 5F6A and Fender reference 8087. The circuit must require a 240 V primary, 325-0-325 V at 230 mA, 6.3 V CT at 4 A, 5 V at 3 A and a 50 V bias tap.

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

Yes, provided the circuit accepts secondary voltages that are slightly lower than the nominal figures specified at 240 V. The 290DEX has no separate 230 V tap, so the heater, bias and high-voltage rails must be checked under load in the completed amplifier.

Can the Hammond 290DEX be used as the 240 V alternative to the Hammond 290DX?

Yes, when the same secondary ratings and mechanical construction are required. Both provide 650 V CT at 230 mA, 50 V bias, 6.3 V CT at 4 A and 5 V at 3 A. The 290DX is designed for 120 V at 60 Hz, while the 290DEX is designed for 240 V at 50/60 Hz.