125ESE Hammond SE Übertrager 2,5k/5k/10k 15W 80mA universal

Hammond 125ESE – universal 15 W single-ended output transformer rated up to 80 mA

The Hammond 125ESE is a universal single-ended output transformer for valve amplifiers. Selecting the appropriate secondary lead allows 2.5, 5 or 10 kΩ primary loads to be matched to 4, 8, 16 or 32 Ω speakers.

Hammond specifies a 15 W transformer rating and a maximum primary DC bias of 80 mA. The 125SE series is intended for general amplifier, repair and guitar applications. For full-bandwidth hi-fi projects, Hammond directs users to the larger 1627–1642 series.

Suitable applications

• General-purpose single-ended valve amplifiers within the 15 W transformer rating
• 6V6 and EL84 circuits using a suitable 5 or 10 kΩ load
• Reduced-power single-ended operating points using 6L6GC, EL34, KT66, KT77, KT88 or 6550 valves at no more than 80 mA
• Radio, guitar-amplifier and mono repairs requiring different speaker impedances
• Experimental builds in which several plate-load and speaker combinations need to be evaluated

Technical data

Product type

Universal single-ended valve output transformer

Primary impedances

2.5, 5 or 10 kΩ, selected through the combination of speaker impedance and secondary lead

Secondary impedances

4, 8, 16 or 32 Ω, depending on the selected primary match

Transformer power rating

15 W

Maximum DC bias

80 mA DC through the primary according to Hammond; a limit rather than an automatically recommended quiescent current

Frequency response

100 Hz to 15 kHz at full rated power, maximum ±1 dB referenced to 1 kHz

Application class

General-purpose and replacement series; not identified by Hammond as a full-bandwidth hi-fi design

Core construction

Butt-stacked 29M6 electrical-steel core with an air gap to reduce DC core saturation

Primary inductance

5.43 H in the current type-specific data sheet at 1 kHz, 1 V with the secondary open

Primary DC resistance

103 Ω between blue and brown, typical or ±20% according to the series information

Black-to-orange secondary DC resistance

167 mΩ typical

Black-to-green secondary DC resistance

225 mΩ typical

Black-to-yellow secondary DC resistance

297 mΩ typical

Black-to-white secondary DC resistance

412 mΩ typical

Black-to-orange secondary inductance

3.70 mH typical at 1 kHz, 1 V with the primary open

Black-to-green secondary inductance

8.20 mH typical

Black-to-yellow secondary inductance

16.2 mH typical

Black-to-white secondary inductance

32.1 mH typical

Dielectric strength

1,500 V RMS

Temperature range

-40 to +105 °C

Construction

Open-frame chassis mounting

Flying leads

Primary and secondary leads at least 12 in or approximately 305 mm long

Dimensions

Approx. 114.3 × 62.2 × 74.7 mm according to the current type-specific drawing

Mounting

Approx. 101.6 mm mounting centres; mounting-hole diameter approx. 4.8 mm

Shipping weight

Approx. 1.36 kg according to Hammond

Primary and secondary connections

Primary winding

Brown–blue; the primary has no tap

Secondary common

Black

Additional secondary leads

Orange, green, yellow and white; the correct lead depends on the required plate load and connected speaker impedance

Connection combinations

10 kΩ primary with 4 Ω

Connect the speaker between black and orange

10 kΩ primary with 8 Ω

Connect the speaker between black and green

10 kΩ primary with 16 Ω

Connect the speaker between black and yellow

10 kΩ primary with 32 Ω

Connect the speaker between black and white

5 kΩ primary with 4 Ω

Connect the speaker between black and green

5 kΩ primary with 8 Ω

Connect the speaker between black and yellow

5 kΩ primary with 16 Ω

Connect the speaker between black and white

2.5 kΩ primary with 4 Ω

Connect the speaker between black and yellow

2.5 kΩ primary with 8 Ω

Connect the speaker between black and white

Comparison within the Hammond 125SE series

Hammond 125DSE

10 W and a maximum 70 mA; smaller version for less heavily loaded single-ended projects

Hammond 125ESE

15 W and a maximum 80 mA; the intermediate universal version in the series

Hammond 125FSE

20 W and a maximum 90 mA; larger version for increased power or current capacity

Hammond 1627–1642

Identified by Hammond as the alternative for an extended 20 Hz to 20 kHz frequency range

Selection and application notes

Plate load is a target value for the complete operating point and should not be selected from the valve type alone. Plate voltage, quiescent current, available voltage swing, plate dissipation and intended output power must all suit the selected primary match.

A lower plate load tends to increase current and may permit more output power, but it also places greater stress on the output valve. A higher plate load tends to reduce current, requires more voltage swing and may reduce the maximum available power.

The 80 mA figure is Hammond’s specified maximum DC bias. It is not a universally recommended quiescent current. Operation at lower current is possible, while bass performance and available power still depend on primary inductance, operating point and speaker load.

The 15 W figure is the transformer rating and does not guarantee 15 W of amplifier output. Small valves and conservative operating points will normally produce substantially less power.

The 100 Hz to 15 kHz range applies at full rated power. A transformer specifically rated for extended low-frequency power should be selected for hi-fi projects requiring substantial output below 100 Hz.

Lethal voltages may be present on the primary winding. The open transformer requires touch-safe installation, and all filter capacitors must be fully discharged before servicing.

Questions about selection and use

Which universal single-ended output transformer suits valve stages requiring a 2.5, 5 or 10 kΩ plate load and up to 80 mA?

Hammond 125ESE provides 2.5, 5 and 10 kΩ primary matching, a 15 W transformer rating and a maximum 80 mA DC bias. The exact plate load must be derived from the valve type, plate voltage, quiescent current and required output power.

Which single-ended output transformer supports 4, 8, 16 and 32 ohm speakers at up to 15 W?

Hammond 125ESE supports these loads, but not every speaker impedance is available with every primary match. Select the correct combination of black and orange, green, yellow or white according to the Hammond connection chart.

Can the Hammond 125ESE be used with 6V6, EL84, 6L6GC, EL34 or KT88 valves?

Yes, these valves may be used at correctly calculated single-ended operating points when a 2.5, 5 or 10 kΩ primary load is suitable and the DC bias does not exceed 80 mA. Actual output power may be substantially below 15 W.

Can the Hammond 125ESE be operated with less than 80 mA of quiescent current?

Yes, 80 mA is the maximum DC bias rather than a required minimum. Lower quiescent current is possible; suitability still depends on the load line, primary inductance, required low-frequency headroom and available voltage swing.