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Conical bore at rotary valves

Posted: Tue Jul 21, 2020 1:49 pm
by dantetuba
Hello all.

My new project will be use an old St Petersburg Eb 3 rotary valves.
My ideia is, let the original 3 rotary but do a 3+1 or 3+2 but the 5th dependent of the 4th system.
I purchase a nice St Petersburg in nickel finish, and the older clock spring have a ratchet adjustment that works great.

I have in hands an old but in good conditions complete cluster 3 rotary valves but with bore size 0,787" we know that the bore size of the Eb St are 0,708".
Now it's the question, I know a better increase bore could be 0,748" but if I use the 4th valve 0,787" than 0,748"?
Maybe I will have some problems if I did this big increase?
Or the other way, change the original cluster in 0,708"and adapt the bigger bore size 0,787", I will need to change the lead pipe. its too much?

I would like to ear some experiences about this and how it works.

Many thanks

Dante

Re: Conical bore at rotary valves

Posted: Mon Jul 27, 2020 12:22 pm
by groovlow
Seems like a big bump, maybe later in the bugle, past the MTS (in the pretzel haha).

The "privilege tones" really work on these horns, plus keeps the weight minimal.
I would get to know the horn well before altering..

Joe H