The trombone, as an instrument, and the evaluation of it, can be seen as having two axes depending on the player or the music (genre). These are resonance and responsiveness to the player (operability/ease of playing), and depending on which is primarily evaluated, even with the same instrument, the results can be completely opposite. For example, I use a HUTTL LINE1000, but those who prioritize operability would give it a low rating, saying, "There's no instrument so thick and difficult to play." In Japan, the evaluation tends to emphasize precision in performance, so responsiveness to the player is valued and reflected in market prices (so HUTTL is very cheap https://aiken-makiss.hatenablog.com/entry/20240401/1711943016 if you're interested). In this regard, the Yamaha professional series from the 1970s (YSL-641, 643, 651), which used a slide made of cupronickel (the material of 50-yen coins and up, not 5-yen coins), is a luxurious construction that is "one of a kind," and is a unique instrument within Yamaha, emphasizing resonance with its red bell. These instruments have established their status as masterpieces, especially overseas (the value of old Yamaha brass instruments is widely agreed upon by those who can play solos). I have explained the details of the 651 in my past listings. https://jp.mercari.com/item/m80846494080 However, although the resonance is superb, it is generally a "heavy model," so whether it is easy to play is a difficult question. However, with this model, there are issues specific to the model, specifically, there is a difference between the early and late models in terms of the balance of resonance and responsiveness (see this article https://aiken-makiss.hatenablog.com/entry/20250227/1740620490 from the middle onwards for the discussion). This listing feels easier to play and has added brilliance to the resonance compared to the late model of the 641. The responsiveness is exceptional. I recommend it to everyone, such as 1st players in wind orchestras. The condition is so good that it's like "it traveled through time?" The slide condition is also top-level. The only problem is shown in the photos from the 13th photo onwards, near the center. I will show a performance sound source in the comments later. For those who understand the value of this miraculous masterpiece.