LL1679 70mA Lundahl SE OPT AÜ 2,5k 4,5k Übertrager transfor.

Lundahl LL1679/70mA – flexible SE output transformer with 2.6, 4.5 or 9.7 kΩ

The Lundahl LL1679/70mA is a large single-ended output transformer with a magnetic design point of 70 mA. Its divided primary and secondary windings provide three different plate-load alternatives.

Depending on the secondary connection, 2.6, 4.5 or 9.7 kΩ can be combined with suitable 4, 8 or 16 Ω loudspeakers. Highly sectioned windings reduce leakage inductance and winding capacitance.

Suitable applications

• 300B single-ended stages using approximately 4.5 kΩ and a suitable operating point
• 2A3, PX4, 45 and related power-triode stages following load-line verification
• Triode-connected 6V6GT, EL84, EL34 or related output valves
• Primary loads of approximately 2.6, 4.5 or 9.7 kΩ
• 4, 8 and 16 Ω loudspeakers with the documented secondary connections
• Mono and stereo SET amplifiers using one transformer per channel

Technical data

Product type

Single-ended valve output transformer

Model version

LL1679/70mA

Magnetic SE operating point

70 mA DC at approximately 0.9 T

Air gap

Approx. 190 µm

Primary inductance

Approx. 40 H

Primary impedances

Approx. 2.6, 4.5 or 9.7 kΩ plate load

Secondary impedances

4, 8 or 16 Ω, depending on primary load and secondary connection

Winding ratio

22+12.5+22+12.5:2+1+2+1

Primary DC resistance

Approx. 160 Ω with all primary sections in series

Secondary DC resistance

Approximately 0.2 to 1.6 Ω, depending on the winding arrangement

Primary leakage inductance

Approx. 8 mH

Maximum primary signal voltage

Approx. 295 V RMS at 30 Hz in single-ended operation

Magnetic power limit at 9.7 kΩ

Approx. 9 W at 30 Hz; not a guaranteed amplifier-output rating

Magnetic power limit at 4.5 kΩ

Approx. 20 W at 30 Hz; not a guaranteed amplifier-output rating

Magnetic power limit at 2.6 kΩ

Approx. 36 W at 30 Hz; not a guaranteed amplifier-output rating

Winding loss

Approximately 0.2, 0.4 or 0.6 dB depending on the primary load

Maximum primary current

200 mA according to the 7 W winding-loss criterion; not a recommended SE quiescent current

Ultralinear tap

Approximately 36–37% in the LL1679 primary; the explicit connection drawing shows push-pull operation

Frequency response of the 70 mA SE version

Not stated separately in the current data sheet; 10 Hz to 70 kHz applies explicitly to the LL1679/PP under the specified conditions

Primary-to-secondary dielectric test

3 kV AC

Winding-to-core dielectric test

1.5 kV AC

Core

Lundahl audio C-core

Construction

Open, unpotted frame intended for installation inside an amplifier enclosure

Dimensions

Approx. 118 × 85 × 78 mm

Mounting pattern

Approx. 53 × 90 mm with four M4 mounting points

Weight

Approx. 2.5 kg

Country of origin

Sweden

Primary loads and loudspeaker connections

9.7 kΩ plate load

Standard connection for 8 Ω using secondary Alternative B or 16 Ω using Alternative C; no standard 4 Ω connection

4.5 kΩ plate load

4 Ω using Alternative B, 8 Ω using Alternative C or 16 Ω using Alternative D

2.6 kΩ plate load

4 Ω using Alternative C, 8 Ω using Alternative D or 16 Ω using Alternative E

Connection view

Follow the Lundahl underside-view drawing exactly for all winding links

Choosing the primary load

2.6 kΩ

Tends towards greater plate current and potentially greater output; check valve and screen-grid dissipation carefully

4.5 kΩ

Intermediate load for many 300B, 2A3 and triode-connected output stages

9.7 kΩ

Higher load with lower current and greater required voltage swing

Selection and safety notes

The 70 mA figure is a magnetic design point rather than a minimum current. Lower quiescent current is possible when the load line, signal swing and required bass reserve remain suitable.

The 200 mA figure describes the winding thermal limit rather than a permitted SE operating point. Likewise, the 30 Hz power figures are not output ratings for the installed valve.

The manufacturer drawing shows the ultralinear connection in push-pull operation. A single-ended screen-grid arrangement requires separate verification of the active winding sections.

The open transformer carries lethal plate voltage and requires a closed, mechanically secure installation.

Questions about selection and use

Which output transformer suits a 300B single-ended stage operating at approximately 70 mA?

Lundahl LL1679/70mA is a flexible starting point for a 300B SE stage and provides 2.6, 4.5 or 9.7 kΩ plate loads. The 4.5 kΩ connection is often relevant to a classic 300B operating point, while the actual load line remains decisive.

Which Lundahl SE output transformer provides three primary loads and several speaker impedances?

Lundahl LL1679/70mA provides 2.6, 4.5 and 9.7 kΩ plate loads with documented 4, 8 or 16 Ω matching. Available speaker impedances depend on the selected primary and secondary connection.

Can the LL1679/70mA operate below 70 mA of quiescent current?

Yes, the LL1679/70mA can operate at a lower quiescent current when the primary load, plate voltage and signal swing remain suitable. The manufacturer does not specify a universal 35 mA minimum.

Can the LL1679/70mA be matched to 4, 8 and 16 ohm loudspeakers?

Yes, the LL1679/70mA can be matched to 4, 8 or 16 Ω depending on the primary load. The 9.7 kΩ connection supports 8 and 16 Ω, while the 4.5 and 2.6 kΩ alternatives also provide 4 Ω configurations.