LL2774 60mA Lundahl SE OPT AÜ 3,5k 16-64-300Ohm Headphone

Lundahl LL2774/60mA – SE headphone output transformer for 16, 64 or 300 Ω

The Lundahl LL2774/60mA is a single-ended output transformer for valve headphone amplifiers. Three secondary arrangements match a valve output stage to headphones rated at 16, 64 or 300 Ω.

The 60 mA version provides 30 H of primary inductance. Depending on the headphone connection, the reflected plate load is approximately 3 or 3.5 kΩ, so the output valve and operating point must suit the selected secondary arrangement.

Suitable applications

• Single-ended valve headphone amplifiers for 16 Ω headphones
• Amplifiers for 64 Ω models with an optional grounded centre tap
• High-impedance 300 Ω headphones
• Correctly designed 300B, EL34, KT88, 6550 or PX25 output stages
• Mono and stereo headphone outputs using one transformer per channel
• High-quality DIY and studio headphone amplifiers with transformer output coupling

Technical data

Product type

Single-ended valve headphone output transformer

Model version

LL2774/60mA

Magnetic SE operating point

60 mA DC

Primary inductance

Approx. 30 H

Maximum primary signal voltage

Approx. 160 V RMS at 30 Hz

Basic turns ratio

(6.8+6.8):(1+1+1+1)

Primary DC resistance per half

Approx. 76 Ω

Total primary resistance in series

Approximately 152 Ω

Secondary DC resistances

Approximately 2.7 or 3.6 Ω depending on the section

Thermal primary-current limit

180 mA according to the 5 W winding-loss criterion; not the magnetic SE operating point

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

Lundahl audio C-core

Winding construction

Three-section dual-coil construction with insulation foil between copper layers

Dimensions

Approx. 97 × 76 × 55 mm

Mounting pattern

Approx. 35 × 75 mm with four M4 mounting points

Weight

Approx. 1.3 kg

Headphone matching

16 Ω connection

Alternative A, approximately 13.6:1 ratio and approximately 3 kΩ reflected primary load

64 Ω connection

Alternative B, approximately 6.8:1 ratio and approximately 3 kΩ reflected primary load

300 Ω connection

Alternative C, approximately 3.4:1 ratio and approximately 3.5 kΩ reflected primary load

Centre tap

The 64 Ω Alternative B can be used with a grounded secondary centre tap

Important selection rule

The nominal headphone impedance and resulting reflected plate load must both suit the output-valve operating point

Output valves and operating point

The 300B, EL34, KT88, 6550 and PX25 are design starting points rather than a universal substitution list. Plate voltage, quiescent current, dissipation, plate resistance and required primary load must be calculated for the actual stage.

The 60 mA figure is the magnetic design point. At substantially lower current, the 30 mA LL2774 version can provide greater bass reserve because of its higher primary inductance.

Headphone protection and safety

Before connecting headphones, verify freedom from DC, switch-on and switch-off transients, correct grounding and output level using a suitable dummy load. Do not use headphones as the first test load for a newly built high-voltage amplifier.

The primary carries lethal plate voltage. Install the transformer in a closed, touch-safe enclosure and wire the headphone socket so that no primary potential can become accessible.

Questions about selection and use

Which valve output transformer suits headphones rated at 16, 64 or 300 Ω?

Lundahl LL2774/60mA provides documented matching for all three impedances. The 16 and 64 Ω arrangements reflect approximately 3 kΩ, while the 300 Ω arrangement reflects approximately 3.5 kΩ to the primary.

Which Lundahl headphone transformer suits a 300B, EL34 or KT88 single-ended stage?

Lundahl LL2774/60mA is a technically useful starting point where the operating point is approximately 60 mA and requires a 3 to 3.5 kΩ primary load. Plate voltage and valve dissipation require complete verification.

Can the 64 Ω connection use a grounded secondary centre tap?

Yes, documented Alternative B for 64 Ω can use a grounded centre tap. The grounding arrangement must suit the complete headphone, chassis and protective-earth design.

Is the LL2774/60mA suitable for a stereo valve headphone amplifier?

Yes, the LL2774/60mA is suitable for stereo using one transformer per channel. Both channels should use identical valve operating points, headphone matching, grounding and core orientation.