LL1664 60mA Lundahl Übertrager 3,0k SE 10W output transformer

Lundahl LL1664/60mA – 3 kΩ SE output transformer for 300B and triode stages

The Lundahl LL1664/60mA is a single-ended output transformer with a fixed nominal match of approximately 3 kΩ to 8 Ω. The current Lundahl data sheet specifies approximately 29 H of primary inductance for the 60 mA version.

This places it between the 50 mA version with 35 H and the 100 mA version with 17 H. It is particularly relevant to classic 300B operating points and other single-ended circuits requiring approximately 60 mA with a target primary load around 3 kΩ.

Suitable applications

• 300B single-ended stages operating at approximately 60 mA and a suitable plate voltage
• Correctly designed PX4, 2A3, AD1 or related triode stages
• Triode-connected EL34, KT88 or related output valves with a suitable load line
• Single-ended stages requiring a primary load around 3 kΩ
• Mono and stereo SET amplifiers; stereo requires one transformer per channel
• 8 Ω loudspeakers where approximately 3 kΩ must be reflected to the primary

Technical data

Product type

Single-ended valve output transformer

Model version

LL1664/60mA

Nominal primary impedance

Approx. 3 kΩ plate load with an 8 Ω loudspeaker

Nominal secondary impedance

8 Ω

Winding ratio

9.6+9.6:1 or (3.2+6.4)+(3.2+6.4):1

Magnetic SE operating point

60 mA according to the current model version

Primary inductance

Approx. 29 H

Primary leakage inductance

Approx. 8 mH with the primary windings in series

Maximum primary signal voltage

Approx. 180 V RMS at 30 Hz

Magnetic power limit

Approx. 10 W at 30 Hz into an 8 Ω load

DC resistance of each primary half

Approx. 74 Ω

Calculated total primary DC resistance

Approx. 148 Ω in series

Secondary DC resistance

Approx. 0.5 Ω

Maximum DC current through one primary winding

200 mA as a winding limit; not the magnetic SE operating current

Winding-to-winding dielectric test

4 kV AC

Winding-to-core dielectric test

2 kV AC

Core

Lundahl audio C-core

Winding insulation

Insulation foil between individual copper layers

Dimensions

Approx. 95 × 75 × 50 mm

Mounting pattern

Approx. 35 × 75 mm with four M4 mounting points

Weight

Approx. 1.35 kg

Country of origin

Sweden according to the current BTB listing

Single-ended connection

The manufacturer connection uses both primary halves in phase and in series. The drawing shows B+ on pin 1, a link between pins 5 and 11 and the plate on pin 7. The 8 Ω secondary is connected between pins 13 and 17.

The drawing uses the underside view. The 33% taps shown for the same LL1664 family refer to push-pull operation and must not be assumed to provide an identical single-ended ultralinear tap.

Reflected load

The fixed ratio reflects approximately 3 kΩ from an 8 Ω speaker. A 4 Ω loudspeaker reflects approximately 1.5 kΩ, while a 16 Ω loudspeaker reflects approximately 6 kΩ. Use a different speaker impedance only where the output-valve circuit deliberately requires that load.

Comparison with the 50 and 100 mA versions

LL1664/50mA

Approx. 35 H, providing greater primary inductance at lower magnetic quiescent current

LL1664/60mA

Approx. 29 H, the intermediate current and inductance version

LL1664/100mA

Approx. 17 H, intended for substantially greater magnetic quiescent current

Selection and safety notes

The 60 mA figure is a magnetic design point rather than a minimum current. A somewhat lower operating current is possible, although the dedicated 50 mA version can provide greater bass reserve where the circuit consistently operates near 50 mA.

The 10 W figure is a transformer limit at 30 Hz. Actual amplifier output depends on the valve, supply voltage, quiescent current, signal swing and permitted plate dissipation.

Lethal voltages may be present on the open transformer. Touch-safe installation and a mechanically adequate chassis are essential.

Questions about selection and use

Which 3 kΩ single-ended output transformer suits a classic 300B stage operating at approximately 60 mA?

Lundahl LL1664/60mA is designed around approximately 60 mA of magnetic quiescent current and provides about 3 kΩ with an 8 Ω load. Plate voltage, bias, plate dissipation and output swing must suit the particular 300B operating point.

Which LL1664 version provides 29 H of primary inductance and 10 W at 30 Hz?

Lundahl LL1664/60mA is documented in the current manufacturer data sheet with 29 H, 180 V RMS primary signal and a 10 W magnetic limit at 30 Hz.

Can the LL1664/60mA also operate at approximately 50 mA?

Yes, the LL1664/60mA can operate at approximately 50 mA with a suitable load line. Where the operating point consistently remains at 50 mA, the dedicated 50 mA version with 35 H can provide greater bass reserve.

Is the Lundahl LL1664/60mA suitable for a stereo 300B amplifier?

Yes, the Lundahl LL1664/60mA is suitable for a correctly designed stereo 300B amplifier using one transformer per channel. Both channels should use identical operating points, loudspeaker loads and core orientation.