You might also consider a used Cerveny 653 F. They play very nice, and the used 4 valvers seem to average around $1500.
I would suggest getting a smaller front valve one instead for a few reasons-
- If you become smitten with Eb and get a bigger horn like a MW or a Willson, the little one will still be worthwhile to keep. Mine rocks at Bydlo and sounds great with trombones (Italian stuff), and if I could play jazz I would play it on this horn.
- I've never played a King Monster, but the little Eb's seem easier to play overall than the bigger ones.
- I say front valve so you can more easily adjust slides for 123 and such.
4 front valve small Eb's are quite rare, so forget about finding one unless you want to get one built. 4 valve Giants/Monsters/... are much more common though still not the rule.
The typical intonation tendencies seem to be a flat 2nd, sharp 4th, and flat 5th. The 2nd is the hard one, but I have been able to get used to playing it in tune on my little King Eb and with the now usable 1st slide I can set Db, C, Bb, and A where I like. With the valve slides set so that 13 is in tune I can actually do almost no pulling/pushing at all, though I dislike playing F in the staff 13. I would like to get 1 trimmed just a little bit, probably on the bottom loop.
My Conn Giant Eb is pretty well in tune, I have just have to think "up" on low Eb and D. Getting the first slide will help with the 5th partial which isn't that bad. Low Eb and E are actually spot on 14 and 24.
The mouthpiece has almost no effect on the intonation of my horns, and actually my Giant plays quite nicely with my PT48 (though the overall horn goes flat). My King has a fantastic low register even with the shallow 30mm mouthpiece I use on it (I'd love to try a 4 valver with a regular mp)! The Giant took a while there but is coming along.
Small top valve York's and small front valve Conn's with the leadpipe before the valves seem to be quite nice. I have TWICE missed out on exceptionally clean Yorks for 600 and 400 respectively. Damnit!
The smaller one is about the size of a Yamaha 621. The Giant is somewhere between a 56J and a 1291. The smallest one is a euphonium. It is as big as a euphonium.

I used to have a little beater Conn stencil that played pretty well-

Here are pictures of a small York and Conn (both of which I was trying to get a few years back!)-
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How common are front valve up bell King Monster Eb's? This one at the Tuba Exchange museum looks slick, but I've never even heard of one otherwise. It looks a lot like my little one doubled before the slide flip-
