Brass instruments are tough. A trumpet or trombone that has spent ten years in a school band room can still play well, and a well-made pro horn can last a lifetime. The problems that matter are small, though, so you have to know where to look. Here's what to check in the photos, what to ask the seller and what to test on arrival.
Start with the photos
Good listings show the whole horn from both sides, the bell, the valves or slide, the serial number and the case. If a listing has one blurry photo, ask for more, and ask for a short video too. Ten seconds of someone pressing each valve or running the trombone slide tells you more than any description.
Red rot
Red rot is the one problem you can't fix with a cleaning. It's a form of corrosion called dezincification. Brass is copper and zinc, and when moisture and oxygen sit in the tubing long enough, the zinc leaches out and leaves a weak, spongy copper that turns pink or red. Yellow brass, the usual material for bells and tubing, is about 30% zinc, which is well into the range where this happens. Gold brass has about 15% zinc, and Bach fits a gold brass leadpipe to its current BTR301 student trumpet because it resists corrosion.
Look where water sits. On a trumpet that's the leadpipe, the pipe the mouthpiece goes into, and the bends of the slides. On a trombone, check the bottom bow of the hand slide and the tuning slide. Zoom in on the photos. Pink blotches or speckles in the brass, especially under worn lacquer, are red rot. Even small spots mean a trip to a repair shop, since the metal underneath has gone weak.
Dents and where they matter
Not every dent matters. A ding in the bell flare is easy to see, but it doesn't stop the horn working the way a dented slide can. Dents in moving parts are a different story. Conn's old care leaflet, packed with every new Conn horn in the 1950s, put it plainly: a dented slide or a sticking valve is a job for an expert, because those parts are fitted to very close tolerances.
So check, in this order:
- Trombone hand slides. Any dent here matters most. More on this below.
- Valve casings. A dent in a trumpet's valve casing can make a piston bind.
- Tuning and valve slides. A dented slide tube won't slide.
- The leadpipe. It's where your air goes in, and where moisture sits.
- The bell. Look last, unless the rim is creased or pulled out of round.
Solder joints and braces
Braces are the small struts that hold the tubes together, and they're soldered in place. Look at each brace in the photos. A gap, a dark line or a brace that sits at an odd angle means it's loose or broken. Big blobs of shiny new solder mean someone has repaired it, which is fine if the work is neat.
Stuck slides, stuck mouthpieces and valves
Ask the seller to pull the main tuning slide and the valve slides on video. Yamaha's care guide says a sluggish tuning slide usually comes down to dirt, corrosion, scratches or a slide that's been twisted out of line. Cleaning and fresh grease fixes the first, and the others need a shop. Don't let anyone use pliers on a stuck one.
Ask whether the mouthpiece comes out. Conn's leaflet warned that forcing a stuck mouthpiece can easily damage the horn, so leave it to a repair shop. Bach gives its BTR301 student trumpet a nickel silver receiver for exactly this reason, to stop mouthpieces sticking.
Valves are harder to judge from photos. Watch the video. Each valve should drop back up quickly and evenly, with no clicks or grinding. Yamaha's guide says valves get sticky without regular oil, and that mixing different valve oils can make them gum up, so a slow valve sometimes just needs cleaning. A valve that's still sticky after a clean and fresh oil, or one that wobbles in its casing, needs a technician.
The trombone slide test
The hand slide is the whole trombone, really. Yamaha says each slide is about 70 cm of very thin tubing, with a gap of around a tenth of a millimeter between the inner and outer tubes. A bend of 0.2 mm over that length is enough to ruin it. You won't see a bend that small in a photo, so test it.
- In the listing. Ask for a video of the slide moving from first to seventh position and back, slowly and then quickly. It should glide the whole way with no sticky spots.
- In the photos. Look along both outer tubes and the bottom bow for dents or creases.
- On arrival. Clean the inner tubes, add a little slide cream or oil, and play for a while. Yamaha says that if the slide turns sluggish 10 to 15 minutes into playing, you should have it checked at a shop.
A slide that fails this test needs a repair before anything else. This applies to every trombone, from a Bach TB300 or Yamaha YSL-200AD to a King 2B, whose jazz slide has thinner walls than a symphony horn's.
Water keys and corks
Water keys are the little levers you press to let out condensation. Each one closes on a cork. Yamaha says those corks go soft with moisture and should be replaced when they wear, since a damaged cork stops the key sealing. Look for a cork in each key in the photos. A missing one is a quick shop fix.
Lacquer wear and relacquered horns
Worn lacquer is normal on an older horn. Conn's leaflet noted that sweat from your hands attacks lacquer, which is why old horns wear through where you hold them. Yamaha adds that bare brass can grow green corrosion, and suggests having a horn refinished if the bare patches are where your hands go. Silver plating darkens naturally too, and Yamaha says that doesn't affect playing.
A horn that looks brand new after decades has probably been refinished. That's fine for a player. Ask the seller what was done with it, because a fresh finish can cover old dent and solder work.
Mouthpiece and case
Check that a mouthpiece is in the photos and that it fits. Trombone mouthpieces come in small-shank and large-shank sizes. A Bach 36B takes a small shank and a Conn 88H takes a large one. Clean any used mouthpiece before it goes near a mouth. Conn called the mouthpiece as personal as a toothbrush. The case matters more than people think, since it's what stops dents in the first place. Look for working latches and a lining that holds the horn snugly.
Rental returns and school surplus
Plenty of used student horns, like the Bach TR300 and Yamaha YTR-2330, come out of school band rooms and rental fleets. Many are good buys, since makers build them for that life. Bach describes its current student trombone as built for the durability rental dealers depend on. Look for asset tags, inventory numbers or a school name engraved on the bell, and ask how the seller got it. Favor horns sold as school surplus with a receipt or auction record. If a school's name is engraved and the seller can't explain it, pass.
Needs work or play-ready?
Read the photos, not the label. A horn is play-ready when the valves or slide move freely, nothing is stuck, there's no red rot and there are no dents in moving parts. If it needs a cleaning, new corks and fresh oil, it's close to play-ready, and you can sort that yourself or at a shop in one visit. Stuck slides, dented hand slides, red rot in the leadpipe and broken braces are real repairs. Price those in or walk away.
Counterfeits are worth one more check on pro horns. BachLoyalist tracks fake Bach Stradivarius trumpets sold online, with tells like long laser-etched serial numbers and the full model number printed on the leadpipe. Our Bach 180S37 page covers them.
For the bigger picture, see our back-to-school buying guide and student vs step-up trumpet guide, or browse all trumpets and trombones.
