LL1623 90mA Lundahl SE OPT AÜ 3,0k 5,6k Übertrager transfor.

Lundahl LL1623/90mA high-end single-ended output transformer

The Lundahl LL1623/90mA is a configurable single-ended output transformer for high-quality valve amplifiers. Its proprietary audio C-core is gapped for a 90 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 provide wide-band operation with low leakage inductance. Depending on the secondary connection, the transformer can feed 4, 8 or 16 Ω loudspeakers.

Suitable applications

• High-end upgrades for 300B single-ended amplifiers
• EL34, 6L6GC, 6550 and KT88 SE projects
• Triode, pentode and triode-strapped output stages
• New amplifier designs requiring selectable impedances

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

Recommended primary DC current

90 mA at 0.9 T core flux density

Air gap

Δ/2 = 190 µm

Primary inductance

30 H for the 90 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 winding connection

Transformer power capability at 30 Hz

13 W at 5.6 kΩ, 25 W at 3.0 kΩ or 50 W at 1.6 kΩ; these figures do not guarantee the amplifier's output power

Insertion loss

Approximately 0.2 dB, 0.5 dB or 0.8 dB, depending on the selected connection

Frequency-response example

7 Hz to 25 kHz within ±0.5 dB using a 650 Ω source, 3.0 kΩ primary load and 8 Ω secondary load

Primary winding

164 Ω DC resistance and 4.6 mH leakage inductance with all primary sections connected in series

Insulation

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

Dimensions

Approximately 118 × 85 × 78 mm

Weight

Approximately 2.5 kg

Mounting

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

Manufacturer

Lundahl Transformers AB, Sweden

Available impedance combinations

5.6 kΩ primary

8 Ω using secondary alternative B or 16 Ω using alternative C

3.0 kΩ primary

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

1.6 kΩ primary

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

Selection and installation notes

The correct primary impedance should be selected from the output valve's load line. The 90 mA designation describes the recommended magnetic DC operating point of this air-gap version rather than the amplifier's output power.

The open-frame transformer is intended for installation inside a closed amplifier chassis. Its terminals may carry lethal anode voltages and require suitable insulation distances and effective protection against accidental contact.

Questions about choosing the right output transformer

Which high-end output transformer is a suitable upgrade for my 300B SET amplifier?

The Lundahl LL1623/90mA is a particularly suitable option when the 300B operates with an approximately 3.0 kΩ primary load and an idle current of up to about 90 mA. Lundahl specifically identifies this version as an ideal choice for many 300B single-ended stages. The actual upgrade benefit depends on whether the existing transformer's bandwidth, primary inductance or core headroom currently limits the amplifier.

Which output transformer can I use for an EL34 single-ended amplifier?

The Lundahl LL1623/90mA suits newly designed EL34 single-ended stages when the load line and idle current match a primary impedance of 1.6, 3.0 or 5.6 kΩ. In the useful 3.0 kΩ to 8 Ω configuration, the 90 mA version provides 30 H primary inductance and a transformer power capability of 25 W at 30 Hz.

Which high-quality SE output transformer suits a 6L6GC, 6550 or KT88?

The Lundahl LL1623/90mA is a flexible choice for purpose-designed single-ended stages using a 6L6GC, 6550 or KT88. Its three primary impedances support different triode, pentode and triode-strapped concepts. The operating point, idle current, load line and required voltage swing must be checked against the selected output valve's data.