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

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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.

The 211 tube, also known as UV-211 or VT-4B, is a directly heated audio triode mainly used as a power tube in high-fidelity audio amplifiers and radio transmitters. Introduced in the 1930s, it is prized for its ability to handle high anode voltages and cathode currents, delivering remarkable output power with low distortion. This high-quality tube is ideal for top-grade audio applications. In single-ended Class A1 it reaches about 20 W RMS, while in push-pull Class B it can deliver up to 260 W of output power.

Introducing the SE211-A1 Transformer:

We are pleased to present our SE211-A1 single-ended output transformer, specially designed for 211 / VT-4B tubes. With a primary impedance of 12 k? and secondary taps of 4/6/8 ?, it is rated for a maximum output of 20 W RMS.

Practical Experience:

To view detailed performance data of the SE211-A1 transformer, please refer to the attached bandwidth graph image. For optimal system configuration, we also recommend exploring our dedicated filament choke for 211 tubes, available on our product page.

Discover the power and versatility of the 211 tube with our SE211-A1 transformer. Thanks to its reliable performance and superb sound quality, it will turn your listening sessions into an unprecedented musical journey.

Images are for illustration only and may not exactly match the product. Items listed may benefit from quantity discounts. When ordering output transformers together with other components such as chokes or power transformers on this site, you can enjoy significant savings compared to the individual unit cost, as illustrated below.

Model SE211-A1
	Type: Single Ended Designed for tube: 211 / VT-4B in Class A1 only (*) Primary impedance: 12 k? Secondary impedances: 4/6/8 ? Maximum power: 20 W RMS Leakage inductance: 17 mH Frequency response: 20 Hz – 24 kHz (–1 dB at 60 mA bias) (*) This does not exclude use with other tubes.
	Dimensions (mm) L 80 H 98 S 121 F 69 F2 80

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Dimension guide

The 300B tube, an icon in the world of hi-fi audio, embodies the essence of sonic fidelity and high-quality sound. With its characteristic warm and enveloping tone, the 300B has captured the hearts of audiophiles worldwide, becoming synonymous with top-tier audio performance.

The Legendary 300B Tube

Originally developed by Western Electric in 1938, the 300B tube was designed for high-fidelity audio amplifiers. Featuring a graphite-coated anode and a tungsten grid, the 300B delivers a rich, detailed and highly musical sound. Its rated output power is about 8–10 watts, but its true magic lies in its ability to reproduce music with exceptional purity and linearity.

Single-Ended Transformers: The Heart of the Sound

Single-ended transformers play a crucial role in shaping the sound of a tube amplifier. Among the most renowned for the 300B are the classic SE3K-300B and SE3K5-300B models, with primary impedances of 3 k? and 3.5 k? respectively. These transformers, using traditional impedance values, are suitable for many publicly available amplifier schematics.

The Special SE4K-300B by Giovanni Mariani

For those seeking the pinnacle of linearity and efficiency, the special SE4K-300B transformer designed by Giovanni Mariani is an outstanding choice. With a 4.4 k? primary impedance, this transformer provides an ideal load line that maximizes the 300B’s linearity. The result is greater precision and sonic clarity, with optimal natural damping and maximized energy transfer to the secondary.

4.4 k? Load Line on the 300B Curves

Maximum Power, No Compromises

Thanks to the SE4K-300B transformer, it is possible to achieve up to 10 W RMS output from the 300B tube without compromising its sonic integrity. However, to fully exploit this transformer’s potential, it is essential to build a high-quality driver stage. A mu-follower with a pair of 6J5 tubes, for example, can provide the clean voltage swing required to drive the 300B.

The 300B tube and single-ended transformers are an extraordinary combination for audiophiles seeking an uncompromising listening experience. From the classic SE3K-300B and SE3K5-300B to the perfection of Giovanni Mariani’s SE4K-300B, there is a wide range of options to meet every audiophile need. Whether you enjoy classical, jazz or rock music, the union of a 300B and a quality transformer will take you on an exciting and unforgettable sonic journey.

Explore Excellent Audio Projects with the SE4K-300B Transformer

• Triodino III and Triodino 3.5 (upgrade) – Single-Ended 300B for NewBye
• Triodino 4 – Single-Ended 300B Stereo – Final Project

Notes: Images shown are for illustration only and may not exactly match the product sold. We nevertheless guarantee the highest quality and precision of our products.

We are also pleased to offer quantity discounts on all our products. By purchasing output transformers together with other items such as chokes, power transformers or any other product in our catalog, you can enjoy significant savings compared to the unit price.

For details on discounts and to take advantage of our special offers, please contact our customer service or browse our website. We are confident you will find valuable opportunities to save while enjoying top-quality audio products and excellent service.

Model SE3K-300B
	Type: Single-Ended Designed for tube: 300B (*) Primary impedance: 3 k? Secondary impedances: 4/6/8 ? Primary resistance: 64 ? Max power: 10 W RMS Leakage inductance: 3 mH Bandwidth: 25 Hz ~ 80 kHz ?3 dB @ 100 mA (*) May also be used with other tubes.
	Dimensions (mm) L 85 H 100 S 104 F 68 F2 58

Model SE3K5-300B
	Type: Single-Ended Designed for tube: 300B (*) Primary impedance: 3.5 k? Secondary impedances: 4/6/8 ? Primary resistance: 86 ? Max power: 10 W RMS Leakage inductance: 3.4 mH Bandwidth: 20 Hz ~ 75 kHz ?3 dB (*) May also be used with other tubes.
	Dimensions (mm) L 85 H 100 S 104 F 68 F2 58

Model SE4K-300B
	Type: Single-Ended Designed for tube: 300B (*) Primary impedance: 4.4 k? Secondary impedances: 4/6/8 ? Max power: 15 W RMS Leakage inductance: 24 mH Bandwidth: 10 Hz ~ 46 kHz ?3 dB (70 mA bias) (*) May also be used with other tubes.
	Dimensions (mm) L 100 H 120 S 110 F 85 F2 70

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Dimension key