LL1620 80mA Lundahl SE OPT AÜ 3,3K 6,0k Übertrager transfor.

Lundahl LL1620/80mA single-ended output transformer

The Lundahl LL1620/80mA is a configurable single-ended output transformer for powerful valve amplifiers. Its audio C-core is factory-gapped for an 80 mA operating point and supports primary loads of 3.3, 6.0 or 11.5 kΩ.

Highly sectioned windings and a low-capacitance winding technique provide wide-band operation with low leakage inductance. This version is particularly interesting for 300B, EL34, KT88, 6550 and comparable output stages when their load line and idle current suit the transformer.

Suitable applications

• 300B single-ended amplifiers operating at approximately 60 to 80 mA
• EL34, KT88 and 6550 SE stages requiring roughly 3 to 4 kΩ
• 6L6GC and KT66 designs using a 3.3 or 6.0 kΩ primary load
• High-end upgrades and new amplifiers for 4 or 8 Ω loudspeakers

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

80 mA at 0.9 T core flux density

Air gap

Δ/2 = 250 µm

Primary inductance

45 H for the 80 mA version

Primary load impedances

3.3 kΩ, 6.0 kΩ or 11.5 kΩ, including transformer copper resistance

Secondary load impedances

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

Transformer capability at 11.5 kΩ

13 W at 30 Hz with approximately 0.2 dB transformer loss

Transformer capability at 6.0 kΩ

25 W at 30 Hz with approximately 0.5 dB transformer loss

Transformer capability at 3.3 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 output power

Primary DC resistance

308 Ω with all primary sections connected in series

Primary leakage inductance

11 mH with all primary sections connected in series

Maximum primary signal voltage

380 V RMS at 30 Hz in single-ended operation

Thermal winding limit

150 mA at approximately 7 W winding dissipation; this value must not be used as the permissible SE idle current

Insulation

3 kV between primary and secondary windings and 1.5 kV between 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

Manufacturer and origin

Lundahl Transformers AB, made in Sweden

Available impedance combinations

11.5 kΩ primary

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

6.0 kΩ primary

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

3.3 kΩ primary

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

Selection notes

The nominal primary impedance is a target range rather than an exact calibration value. An output stage calculated for approximately 3.5 kΩ may operate appropriately with the 3.3 kΩ connection, provided that idle current, plate dissipation and signal swing remain within safe limits. The loudspeaker's actual impedance also changes the reflected load seen by the valve.

A slightly lower primary load generally permits more current and output power but places greater demand on the output valve. A higher load is often more conservative, requires additional voltage swing and normally reduces maximum output.

The open-frame transformer is intended for installation inside a closed amplifier chassis. Its primary terminals may carry lethal voltages.

Questions about choosing the correct SE output transformer

Which high-end output transformer suits a 300B single-ended amplifier?

The Lundahl LL1620/80mA is an attractive choice for 300B operating points using approximately 60 to 80 mA idle current and a desired primary load of roughly 3 to 4 kΩ. Its 3.3 kΩ connection is close to many traditional 300B load lines. The 6 kΩ connection can support a more conservative design using lower current and greater voltage swing.

Which Lundahl output transformer suits an EL34, KT88 or 6550 single-ended amplifier?

The Lundahl LL1620/80mA suits correctly designed EL34, KT88 and 6550 SE stages when idle current does not exceed approximately 80 mA. The 3.3 kΩ connection is attractive for many power-oriented conditions, while 6.0 kΩ may suit higher-voltage, lower-current or triode-connected operation. The final valve load line remains decisive.

Is the LL1620/80mA suitable as an upgrade for an existing valve amplifier?

Yes, provided that the existing amplifier is single-ended and its primary load, idle current, output level and 4 or 8 Ω secondary load match the LL1620/80mA. Mounting dimensions, feedback polarity, phase relationship and power-supply capability must also be checked before replacement.

Can the LL1620/80mA operate with less than 80 mA of idle current?

Yes, a lower idle current is possible and provides additional magnetic headroom. When a design will operate permanently at only about 40 to 60 mA, however, a Lundahl version with a smaller air gap and higher primary inductance may be a better choice for maximum low-frequency reserve.