Unison Research Triode 25 Black Edition

The Triode 25 Black Edition lets you choose the character of your power tubes. Its four KT77 Gold Lion output tubes run in ultralinear pentode mode for 50 W, or in triode mode for 30 W, and Unison Research built three digital inputs in as standard.

Two modes from one set of power tubes.

The Design

To improve the Triode 25, Unison Research gathered its strengths and pushed further toward higher sound quality. The circuits were revised in their signal path and power management, and Unison Research says distortion was reduced and power increased. A specially designed circuit lets the power tubes operate in either triode or pentode mode. The input selection circuit uses the same technology as the company's most prized products, with extreme attention to ground paths and channel separation, and where possible the audio signal travels inside quality coaxial cables.

The output stage is a push-pull, ultralinear Class AB design built around four KT77 Gold Lion tubes, with the tap at 60% in ultralinear mode, and bias is adjustable. Two ECC83 and one ECC82 Gold Lion tubes handle the signal stages. Feedback is selectable between 10 dB and 12 dB.

Inputs and Connections

There are three RCA line inputs plus USB, S/PDIF, and Toslink digital inputs, which every Black Edition amplifier includes as standard. The relay input selector uses Return GND technology. Outputs are a stereo RCA subwoofer output and a line out.

Where It Fits

Choose the Triode 25 Black Edition if you want to hear the difference between triode and pentode operation in your own room and with your own speakers, and want a streamer or computer to connect directly. We're happy to help you decide between the Triode 25, the S6 Black Edition, and the other Black Edition models.

Press Recognition

Hi-Fi News covered the Triode 25 Black Edition when the Black Edition range appeared, as part of its coverage of Unison Research's upgraded Triode 25 (HFN, July 2025). Unison Research, founded in 1987 in Treviso by a group of audiophiles led by Giovanni Maria Sacchetti, is recognized as Italy's leading maker of tube amplifiers.

Questions about triode versus pentode operation, or speaker matching? Give us a call.

Specifications

• Type: Tube integrated amplifier
• Output stage: Push-pull, ultralinear, Class AB
• Output power: 50 W in pentode mode; 30 W in triode mode
• Signal tubes: 2 x ECC83 Gold Lion; 1 x ECC82 Gold Lion
• Power tubes: 4 x KT77 Gold Lion, push-pull
• Working mode: Triode, or ultralinear with the tap at 60% (power tubes)
• Bias: Adjustable
• Input selector: Relay, with Return GND technology
• Inputs: 3 RCA line; 1 USB; 1 S/PDIF; 1 Toslink
• Outputs: 1 stereo RCA subwoofer; 1 line out
• Feedback: Selectable, 10 dB to 12 dB
• Bandwidth (-1 dB): 10 Hz to 50 kHz
• Dimensions: 30 x 45 x 20 cm (12 x 18 x 8 in)
• Weight: 20 kg
• Maker: Unison Research, handcrafted in Italy