If you have speakers in the 100db efficiency range, the 45 tube is the king of SET tubes. The Gemini will deliver about 2.5 watts using the 45 tube. However, flip a switch on the bottom and you can also use 2A3 tubes which can give you about 3.5 watts.

In addition to the 45 and 2A3s, the amps use one 6V4 / EZ80 and one 417A / 5842 each. Gordon Rankin uses the best build quality with Magnequest transformers as well. I will include the tubes pictured as backups and also include a pair of NOS 45s, 2A3s, 6V4s and 5842s. If you desire more tubes, I can also provide them as I have a fair supply which I'll be selling.

The Wavelength Audio Gemini is what's sometimes classified as a "boutique product": one handbuilt by its designer, with the micro-tuning of design, attention to detail, and level of craftsmanship that this implies. While not inexpensive, it's actually the lowest-priced amplifier that Wavelength makes. The Gemini's need for high-sensitivity speakers and its inability to exploit those speakers' full dynamic range mean that it's not the amplifier for everyone—but then, I don't know of any amplifier that is. What the Gemini offers, particularly when equipped with 45 tubes, is transparency, detail, harmonic "rightness," and an ability to maximize musical values with a minimum of electronic artifacts. For those who value these characteristics more than sheer loudness, the Gemini may in fact be the ideal amplifier. https://www.stereophile.com/tubepoweramps/351/index.html

Here's a review: JeffR review

BTW: The large hole in the bottom of the amps allows you to flip the switch to change between 45 and 2A3 tubes.

I can provide more pictures, just ask.