Tube amplifier output transformers

All OPTs are built in our dual coil single C-core style and can be ordered with a choice of core air-gap for Push-Pull or Single-Ended applications. Most of our OPTs can be configured for different primary and secondary impedances.
The use of C-cores with well-defined air-gap results in an almost constant inductance throughout the whole operating voltage range. For SE transformers, the primary inductance variation due to signal level is less than 7%.

Most of the transformers below are available with amorphous iron C-cores. The amorphous cores are considered to have sonic advantages, but the signal level capability with amorphous core is about 30% less than with a conventional silicon-iron C-core.


Tube output

Primary impedance Secondary impedance Max power capability at 30 Hz, Push-Pull Max power capability at 30 Hz, Singel Ended WeightTransformer type Configuration
0.6 k4 Ω700W140W4.5 kgLL1693
0.65 k4 Ω250W50W2.5 kgLL1627C
1.0 k4 Ω360W70W4.5 kgLL1693B
1.2 k4 Ω125W25W2.5 kgLL1627B
1.2 k8 Ω125W25W2.5 kgLL1627C
1.2 k16 Ω125W25W2.5 kgLL1627D
1.2 k4 Ω180W36W2.5 kgLL2752C
1.2 k8 Ω180W36W2.5 kgLL2752D
1.6 k4 Ω250W50W2.5 kgLL1623B
1.6 k8 Ω250W50W2.5 kgLL1623C
1.6 k16 Ω250W50W2.5 kgLL1623D
2 k4 Ω105W21W2.5 kgLL2752B
2 k 8 Ω105W21W2.5 kgLL2752C
2 k16 Ω105W21W2.5 kgLL2752D
2.3 k8 Ω62W13W2.5 kgLL1627B
2.3 k16 Ω62W13W2.5 kgLL1627C
2.3 k8 Ω180W35W4.5 kgLL1693
2.3 k16 Ω180W35W4.5 kgLL1693
2.6 k4 Ω188W36W2.5 kgLL1679C
2.6 k8 Ω188W36W2.5 kgLL1679D
2.6 k16 Ω188W36W2.5 kgLL1679E
3.0 k4 Ω125W25W2.5 kgLL1623B
3.0 k8 Ω125W25W2.5 kgLL1623C
3.0 k16 Ω125W25W2.5 kgLL1623D
3.0 k8 Ω55W10W1.4 kgLL1664-
3.3 k4 Ω250W250W2.5 kgLL1620C
3.3 k8 Ω250W50W2.5 kgLL1620D
3.3 k16 Ω250W50W2.5 kgLL1620E
4.5 k
4 Ω105W20W2.5 kgLL1679B
4.5 k8 Ω105W20W2.5 kgLL1679C
4.5 k16 Ω105W20W2.5 kgLL1679D
4.6 k8 Ω45W10W2.5 kgLL2752B
4.6 k 16 Ω45W10W2.5 kgLL2752C
5.0 k8 Ω40W8W1.4 kgLL1663-
5.5 k4 Ω320W60W4.0 kg
5.5 k5 Ω40W8W1.4 kgLL1682-
5.5 k8 Ω320W60W4.0 kgLL1688D
5.5 k16 Ω320W60W4.0 kgLL1688E
5.6 k8 Ω62W13W2.5 kgLL1623B
5.6 k16 Ω62W13W2.5 kgLL1623C
6.0 k4 Ω125W25W2.5 kgLL1620B
6.0 k8 Ω125W25W2.5 kgLL1620C
6.0 k16 Ω125W25W2.5 kgLL1620D
6.5 k4 Ω350W50W2.5 kgLL9202C
6.5 k8 Ω250W50W2.5 kgLL9202D
6.5 k16 Ω250W50W2.5 kgLL9202E
9.0 k8 Ω160W30W4.6 kgLL1691-
9.2k 4 Ω160W30W4.0 kgLL1688B
9.2 k8 Ω160W30W4.0 kgLL1688C
9.2 k16 Ω160W30W4.0 kgLL1688D
9.7 k8 Ω45W9W2.5 kgLL1679B
9.7 k16 Ω45W9W2.5 kgLL1679C
11 k 8 Ω95W18W4.6 kgLL2755-
11 k4 Ω125W25W2.5 kgLL9202B
11 k8 Ω125W25W2.5 kgLL9202C
11 k16 Ω125W25W2.5 kgLL9202D
11.5 k8 Ω62W13W2.5 kgLL1620B
11.5 k16 Ω62W13W2.5 kgLL1620C
16 k8 Ω-5W1.4 kgLL2735B -
16 k4 Ω-5W1.4 kgLL2735B (2735F)-
16 k16 Ω-5W1.4 kgLL2735B (2735F)-
20 k8 Ω160W30W4.6 kgLL1691B-
23 k8 Ω62W13W2.5 kgLL9202B
23 k16 Ω62W13W2.5 kgLL9202C
  • If you need to more easily switch between different speaker impedances on our output transformers LL1620, LL1623 and LL1627, this sheet suggests two different wiring alternatives where the OPT secondary is reconnected using only three jumpers.
  • The LL1620CFB is a special version of the LL1620 where the primary windings have been split to allow for cathode feedback connections.
  • The 2.5kg and the 1.4 kg transformers above are available with amorphous iron C-cores. We expect all application parameters to be similar for the amorphous core and the silicon iron cores, except that the amorphous cores signal handling capability is slightly smaller.

From a purely engineering point of view, we cannot justify the fairly high price of our amorphous core OPTs. But we have actually received a lot of praise for their sound quality, such as this report.

When considering testing an amorphous core transformer, please note that they are said to require much longer break in time than what is normally required for silicon-iron cores.