Does anyone know the bore size of the valve sections on the Yamaha YBL-611 and YBL-612 series bass trombones? The only specifications I can find are the slide bore of .563”. I’m mostly curious how the “shepherd’s crook” of the F valve might work for a project I have in mind.

Thanks, for any help or info that may be provided.

Pretty sure they're .593 ish just like everyone else

I have put my calipers in my bag, so I'll have an answer for you once I get home.

[quote="Burgerbob"]Pretty sure they're .593 ish just like everyone else[/quote] I got about .594-.595 in the inside of the Eb crook and the F tuning slide. So confirmed.

This was on a YBL-612RII. I do know that the previous "generation" of the 611 and 612 used slightly different valves with brass casings, but I don't believe Yamaha would have changed any of the tubing.

Thanks, Aidan and David.

[quote="tbonesullivan"]<QUOTE author="Burgerbob" post_id="237906" time="1710893691" user_id="3131">
Pretty sure they're .593 ish just like everyone else[/quote] I got about .594-.595 in the inside of the Eb crook and the F tuning slide. So confirmed.

This was on a YBL-612RII. I do know that the previous "generation" of the 611 and 612 used slightly different valves with brass casings, but I don't believe Yamaha would have changed any of the tubing.
</QUOTE>

My 611R II measures .593 . Does the "II" mean second generation, or does the "611" mean previous generation? I don't know this line very well.

[quote="AtomicClock"]My 611R II measures .593 . Does the "II" mean second generation, or does the "611" mean previous generation? I don't know this line very well.[/quote] There were a few versions of the YBL611 and YBL612. I've actually never been clear on what the "II" means after the model number. I've seen models with the "II" that have the early brass valve casings and string linkages with non-split triggers.

The 611 and 612 are pretty much the same trombone, and originally I think the only difference was the 611 had a red brass bell, while the 612 had a yellow brass bell. Valve sections and slides were pretty much identical, and had a double thumb trigger with string linkages. They were both originally produced in Bb/F/Eb, however later a D crook was produced.

At some point, the valve casings were redesigned, and were made from nickel silver instead of yellow brass. I think the stop plates were also redesigned, and this probably coincided with the introduction of the split triggers. By the point, having two different bass trombones that differed only in bell material didn't make sense within the yamaha naming scheme, and the YBL611 became the YBL612R.

I remember someone posting an advertisement of the YBL611 or 612 from the 1970s. They were in production for quite a number of years.