LL1623 120mA Lundahl SE OPT 3,0k 5,6k Übertrager transfor.

Lundahl LL1623/120mA for high-current single-ended amplifiers

The Lundahl LL1623/120mA is a high-current single-ended output transformer for powerful valve amplifiers. Its Swedish audio C-core is factory-gapped for a 120 mA operating point and supports primary loads of 1.6, 3.0 or 5.6 kΩ.

Highly sectioned windings and a low-capacitance winding technique are designed for wide-band operation with low leakage inductance. This version is particularly attractive for 300B XLS, 320B, 520B, KT120, KT150 and comparable high-current output valves.

Suitable applications

• 300B XLS, 320B and 520B single-ended amplifiers
• High-power KT120 and KT150 SE output stages
• High-current SET and monoblock amplifier projects
• Upgrades for amplifiers operating at up to approximately 120 mA

Technical specifications

Transformer type

Open-frame single-ended valve-amplifier output transformer

Core construction

Lundahl audio C-core with highly sectioned windings and a low-capacitance winding technique

Nominal operating point

120 mA of primary DC current at the intended core operating level

Air gap

Δ/2 = 250 µm

Primary inductance

23 H for the 120 mA version

Primary load impedances

1.6 kΩ, 3.0 kΩ or 5.6 kΩ, including transformer copper resistance

Secondary load impedances

4 Ω, 8 Ω or 16 Ω, depending on the primary connection

Transformer capability at 5.6 kΩ

13 W at 30 Hz with approximately 0.2 dB transformer loss

Transformer capability at 3.0 kΩ

25 W at 30 Hz with approximately 0.5 dB transformer loss

Transformer capability at 1.6 kΩ

50 W at 30 Hz with approximately 0.8 dB transformer loss

Power-rating note

These figures describe the magnetic transformer limit at 30 Hz and do not guarantee the amplifier's electrical output power

Primary DC resistance

164 Ω with all primary sections connected in series

Primary leakage inductance

4.6 mH with all primary sections connected in series

Maximum primary signal voltage

270 V RMS at 30 Hz in single-ended operation

Thermal winding limit

210 mA at approximately 7 W winding dissipation; this is not the intended single-ended idle-current rating

Insulation

3 kV between primary and secondary windings and 1.5 kV between windings and core

Dimensions and weight

Approximately 118 × 85 × 78 mm at approximately 2.5 kg

Mounting

Four M4 mounting holes on an approximately 90 × 53 mm pattern; 5.08 mm pin spacing

Manufacturer and origin

Lundahl Transformers AB, made in Sweden

Available impedance combinations

5.6 kΩ primary

Configurable for 8 Ω or 16 Ω loudspeakers

3.0 kΩ primary

Configurable for 4 Ω, 8 Ω or 16 Ω loudspeakers

1.6 kΩ primary

Configurable for 4 Ω, 8 Ω or 16 Ω loudspeakers

Valve-selection notes

The optimum primary load is determined from the output valve, anode voltage, idle current and intended output power. A 3.0 kΩ load is a useful starting point for many powerful triodes and beam tetrodes. The 1.6 kΩ connection is intended only for suitably current-capable operating points, while 5.6 kΩ requires greater voltage swing and normally less current.

The open-frame transformer should be installed inside a closed amplifier chassis. Its primary and anode terminals may carry lethal voltages.

Questions about choosing a high-current output transformer

Which output transformer suits a 300B XLS, 320B or 520B single-ended amplifier?

The Lundahl LL1623/120mA is a particularly attractive choice for powerful 300B XLS, 320B and 520B operating points. Its 3.0 and 5.6 kΩ connections support different voltage and current arrangements. Idle current may approach the nominal 120 mA design point, but the load line, plate dissipation and power-supply reserve must be calculated together.

Which Lundahl output transformer suits a KT120 or KT150 single-ended amplifier?

The Lundahl LL1623/120mA suits correctly designed KT120 and KT150 SE stages. A 3.0 kΩ primary is a useful starting range for many operating points; 1.6 kΩ permits more current, while 5.6 kΩ can support a more conservative high-voltage design. The final load line, idle current and screen-grid conditions remain decisive.

Is the LL1623/120mA suitable as an upgrade for a powerful SE amplifier?

Yes, when the existing amplifier requires approximately 1.6, 3.0 or 5.6 kΩ and its idle current remains within the 120 mA design point. Output power, loudspeaker impedance, mounting space, feedback and transformer phase must also be compatible.

Can the LL1623/120mA operate with less than 120 mA of idle current?

Yes, a lower idle current is possible and provides additional magnetic reserve. When a design will operate permanently at approximately 70 to 90 mA, the LL1623/90mA may offer better low-frequency reserve through its 30 H primary inductance compared with 23 H for the 120 mA version.