There are no solutions, only tradeoffs --- and a horn is the sum of its parts. In other words, there is no perfect horn but only a horn that has the right tradeoffs for you, what you are using it for, and those interactions with the mouthpiece you're using with it.
So with that said, you aren't the first person to try to attribute a large part about what they do or do not like about a horn to the valve! And the approach isn't totally invalid, there is a lot that can go wrong with the valve you have. Thayers can be finnicky too and require a little more maintenance than others, so there may be something wrong with it. Your cheapest, and probably best, solution would be to take it to a tech first, to make sure that the whole horn is in good working condition. If you replace the thayer with a custom rotor solution, it may well make the horn better... but that doesn't mean that the rotor is superior. It means that the rotor may work better for you & the rest of the horn OR that there was something wrong with the valve in the first place. And it's a LOT cheaper to fix a valve than buy a new one, especially on a horn that isn't meant to be interchangeable like the Getzen 3047AF.
So with that said, the Getzen 3047 (I'm assuming this is the horn you're talking about since that's the current production model) actually IS an Edwards valve. The Custom series is just a collection of the most popular components with the difference being that the receivers are not the same on the bell section, so you can't pop a new Edwards bell, valve section, or slide on it. However, it isn't unreasonably difficult to make these alterations, but you're looking at a procedure that probably won't be cheap.
When you say it "screws you over" when you play "in the range its meant for", I'm assuming you mean that you don't like the low range on it (sub
). If this is a problem with the linkage, that too is much cheaper than replacing the whole thing! Instrument Innovations apparently has a lever for thayer valves that works very well, though I have no experience with it. The way you phrase it though, I'm going to guess you don't like the responsiveness in the register. If that is the case, obviously make sure that you aren't blaming something that isn't the fault of the horn -- for example, if you play another similar 547 horn and it has a fine low register, then again it might be something with the thayer or possibly that the thayer isn't the best fit for the horn. I hestitate to suggest the latter since, as I mentioned, the Getzen 3047 is a population combination of components so it might be the case, but there are other things to check first.
One of them is the leadpipe. If, for example, you try a Bach 42B that you really like the low register on, you should know that the leadpipe on those are much closer to the "1" your Getzen should have. If you've been playing on the 3, you might want to give the "1" a shot. Again, its a lot cheaper than replacing your valve. Leadpipes don't fix all your problems, but they certainly can go a long way towards making it right.
If you really want to swap the valve out, you do have some good options. You could get an Instrument Innovations thayer. They're the ones that are currently going on the infinity series Bachs. Several of the techs here really like them. I have a friend who just had a Bass valve section built with these and he really likes them. The benefit to this is you'd only be out the cost of the valve + labor. There's no guarantee it would make it play better, but again, these are getting a lot of good press recently.
If you wanted to have a drop in valve built, it is possible to get a gooseneck for the 3047. They're actually
not too expensive either. Then you could have your tech cut & retaper the neckpipe portion of it to fit the valve that you're installing. Lots of aftermarket options. Rotax, Instrument Innovations Rotors, any of the Shires valves, Hagmann, etc. In each case though, you're probably looking at spending at least $1500, though probably not more than $2500. If you get used parts, it is possible to go lower, but you have to be patient.
In defense of getting a rotor put on it, I had a colleague when I was in my undergraduate who had an Edwards that happened to be the same components as the 3047AF but it was converted to a Greenhoe rotor. It played like an absolute dream, although he eventually switched to a Shires. Though it wouldn't be my first choice unless I've checked out some of the other recommendations I mentioned earlier like making sure the valve works, that other valves work better for you on other horns, and making sure a leadpipe swap won't go a long way towards what you're looking for.
