I’m excited to introduce my latest product: the SE4K5-EL84 Single-Ended Output Transformer, specially designed for audiophiles seeking outstanding sonic performance with EL84, ECL82, PCL82, ECL85 and PCL85 tubes. Custom-built for the EL84, this transformer represents the pinnacle of audio perfection, delivering an unparalleled listening experience.

Design

Unlike conventional transformers, I focused on providing a tailor-made solution for each tube. While carefully studying the EL84 datasheet, I noticed an intriguing detail: although most transformer suppliers specify a primary impedance around 5 k or 5.2 k, the datasheet actually suggests two biasing options with similar power output.

At a primary impedance of 5.2 k, third harmonic distortion is around 9.5 % and second harmonic about 2 %. The alternative is a 4500 ohm primary, which lowers third harmonic to 8 % and raises second to 5 %. I found the 4500 ohm bias more balanced, so—going against mainstream practice—I designed a transformer specifically for the EL84 with a 4500 ohm primary impedance.

The same reasoning applies to ECL82 and PCL82 tubes, as their datasheets also point to a recommended 4500 ohm operating condition.

Field Testing

I built and tested the transformer directly in a Pico 8084 channel, a project using an EL84 output stage driven by an EABC80. The measurements were remarkable, yielding about 3 – 3.5 W RMS to the speaker. You can also see it in action on the Scherzo Rework 2 with a PCL82 here.

Sound Performance

The SE4K5-EL84 preserves the warm, enveloping character of EL84 tubes, providing pure and detailed reproduction. A generously sized core ensures a truly Hi-Fi experience.

Graphs and Measurements

All detailed graphs and measurements are published in my article, offering a complete overview of the SE4K5-EL84’s performance. The frequency response is 15 Hz / 33 kHz –1 dB @ 1 watt.

Square waves at 100 Hz – 1 kHz – 10 kHz

Model SE4K5-EL84
	Type: Single Ended Compatible tubes: EL84 – ECL86 – PCL86 – ECL82 – PCL82 – ECL85 – PCL85 (*) Primary impedance: 4500 ohm Secondary impedances: 4 / 6 / 8 ohm Primary resistance: 285 ohm Maximum power: 5 W RMS Leakage inductance: 33 mH @ 1 kHz Primary inductance: 26 H @ 100 Hz Bandwidth: 15 Hz – 33 kHz –1 dB (*) It can also be used with other tubes.
	Dimensions (mm) L 60 H 77 S 80 F 51 F2 46

Click here to order.

Dimension legend

All items for sale are CE compliant

Conclusions

In conclusion, the SE4K5-EL84 Single-Ended Output Transformer offers a unique design approach aimed at achieving the best performance from EL84 tubes. Invest in customized audio quality with the SE4K5-EL84 and experience your favorite sound as never before.