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Lundahl LL2766/50mA – compact SE output transformer with 3 or 6 kΩ

The Lundahl LL2766/50mA is a compact single-ended output transformer for smaller valve power amplifiers. Depending on the secondary arrangement, it provides approximately 3 or 6 kΩ primary loads with matching for 4, 8 or 16 Ω loudspeakers.

The 50 mA version provides 25 H of primary inductance and uses a high-flux Lundahl audio C-core. It is particularly relevant where lower weight and compact dimensions are more important than the headroom of larger Lundahl transformers.

Suitable applications

• Correctly designed EL84 and 6V6GT single-ended output stages
• Small triode or triode-connected pentode amplifiers
• Primary loads of approximately 3 or 6 kΩ
• 4, 8 and 16 Ω loudspeakers using the documented winding alternatives
• Mono and stereo valve amplifiers using one transformer per channel
• Compact audio DIY projects with moderate output power

Technical data

Product type

Compact single-ended valve output transformer

Model version

LL2766/50mA

Magnetic SE operating point

50 mA DC with the complete primary connection

Primary inductance

Approx. 25 H

Primary impedances

Approx. 3 or 6 kΩ plate load

Secondary impedances

4, 8 or 16 Ω, depending on primary load and winding alternative

Basic turns ratio

40+40:2+2+1+1

DC resistance per primary section

Approx. 140 Ω

Total primary resistance in series

Approximately 280 Ω

Secondary DC resistances

Approx. 0.8 Ω for the larger and 0.2 Ω for the smaller secondary sections

Thermal winding-current limit

120 mA through one primary section at 4 W loss; not the magnetic SE operating point

Magnetic power limit at 6 kΩ and 8 Ω

Approx. 2.5 W at 30 Hz

Magnetic power limit at 3 kΩ and 8 Ω

Approx. 4 W at 30 Hz

Numerical frequency response

Not stated in the current public data sheet

Primary-to-secondary dielectric test

4 kV AC

Winding-to-core dielectric test

2 kV AC

Core

High-flux Lundahl audio C-core

Dimensions

Approx. 73 × 61 × 53 mm

Mounting pattern

Approx. 36 × 56 mm with four M3 mounting points

Weight

Approx. 0.75 kg

Primary loads and loudspeaker connections

6 kΩ to 4 Ω

Winding Alternative A with an approximate ratio of 79:2

6 kΩ to 8 Ω

Winding Alternative B with an approximate ratio of 79:3

6 kΩ to 16 Ω

Winding Alternative C with an approximate ratio of 79:4

3 kΩ to 4 Ω

Winding Alternative B

3 kΩ to 8 Ω

Winding Alternative C

3 kΩ to 16 Ω

Winding Alternative D with an approximate ratio of 79:6

Choosing the primary load

A 3 kΩ load tends towards greater plate current and valve stress but can allow more output where the operating point is suitable. A 6 kΩ load tends to reduce current and requires greater voltage swing.

The 30 Hz power figures are magnetic transformer limits rather than guaranteed amplifier output. The output valve, supply voltage, quiescent current and permitted dissipation remain decisive.

Safety notes

Lethal plate voltage can be present on the open transformer. Install the LL2766 in a closed, touch-safe enclosure with adequate electrical clearances.

Questions about selection and use

Which compact SE output transformer suits an EL84 or 6V6GT stage operating at approximately 50 mA?

Lundahl LL2766/50mA is a useful starting point with 3 or 6 kΩ plate loads for correctly designed EL84 and 6V6GT single-ended stages. Plate voltage, quiescent current and load line determine the connection.

Which Lundahl SE output transformer provides 3 or 6 kΩ with 4, 8 or 16 Ω connections?

Lundahl LL2766/50mA provides these primary and secondary alternatives in a compact 0.75 kg format. The exact winding arrangement follows the required combination of plate load and loudspeaker impedance.

Can the LL2766/50mA operate at 6 kΩ with an 8 Ω loudspeaker?

Yes, the LL2766/50mA provides documented winding Alternative B for this combination. Under the data-sheet conditions, the magnetic limit at 30 Hz is approximately 2.5 W.

Is the LL2766/50mA suitable for a stereo single-ended amplifier?

Yes, the LL2766/50mA is suitable for stereo using one transformer per channel. Both channels should use identical valve operating points, winding arrangements, loudspeaker loads and core orientation.