I just took delivery of this C.F. Zetsche & Söhne bass trombone in G.

I sold that German straight F bass to a friend, and my small bore Boosey & Hawkes G bass trombone remains nothing more than a decoration thanks to its unusable slide. Neither of these instruments really scratch the itch I've had for many years - a truly modern long bass trombone. Something that feels and plays like an instrument made yesterday, not one made in the 19th century. Something with a modern, plated slide that falls under its own weight. Something that isn't so big that it sounds like a contra, or so small that it will never blend with anything but small bore tenors. Something that is a modern, great-playing bass trombone in every aspect, that just happens to be in a key lower than B-flat.
I figured such a thing didn't exist, and would require me to pony up serious cash one day far in the future to get one made from scratch. But I don't think that'll be necessary anymore, as first impressions of this new arrival tell me it's everything I've ever wanted in a "real" bass trombone.
This instrument has:
- A modern, plated 7-position slide that isn't too heavy, is easy to use with or without the handle, and falls under its own weight.
- A .550" single bore and 10" bell. No more weird or archaic specs; this is exactly what I would expect a modern G bass trombone to be.
- A D-flat attachment (you read that right! Not D, D-flat.) with a very long pull to C and a paddle that is more comfortable to use than some well-known horns (looking at you, every Olds with a valve ever).
- A rotor that, while it looks small, plays very well. Not stuffy, sounds great.
- A nice, gimballed slide handle.
In short, it has everything that my previous two long bass trombones lacked. But more importantly, how does it play?
It plays...like a bass trombone.
It's not a laborious task to play. It doesn't have any dead partials or a difficult high register. It's not stuffy or woofy or uneven. It's just...a bass trombone. I kid you not, this instrument is as easy and natural to play as my B-flat bass trombones. It seems to require no more effort other than remembering where to put the slide. It just...does what you want it to, like a good modern instrument should. It has a great big open sound, but one that is still 100% bass trombone. Not contra, not tuba on a stick, not woofy trombone.
This instrument is proof that longer instruments don't have to suck. That G and F bass trombones being cumbersome beasts of burden is not actually a function of the instrument's length at all, but just that that specific model isn't good. I've only had a chance to play it for a few minutes and I am already over the moon with it. My dream is real, and it's mine! (And before you ask, yes I will be putting a modern independent valve set on it.)
Just for fun, here's a shot comparing this German G bass (top) with my British G bass (bottom). Pretty interesting how different the slide-bell relationships are.

So what I'd like to know about this instrument is...when was it made, and why?