DIY 802 field coil drivers may be a reality!!

[BillWojo]

Surface rust is not a real problem except that indicates that the protective coating (zinc or cadmium plating) is used up. The problem is when the rust is deeper and changes the physical dimensions of the gap. I don't have the math handy to prove it but I highly suspect that even a small change in the gap width will have a much larger change in the gap magnetic field strength.
Thanks guys.

BillWojo

[mah]

Bill, look what this project could lead to:

Western Electric 13A Horn


Western Electric 16A Horn

[BillWojo]

Marshall, thanks for the links. What I find very interesting is a bit of information in the first link.
Seems the Western Electric 13A horn was actually manufactured by the Victor Talking Machine Company. Look at the brass plate in the last picture.
I live less than 15 miles from the old plant. That's really cool that these were built locally. Now if I could only find a set. LOL

BillWojo

[GM]

The problem is when the rust is deeper and changes the physical dimensions of the gap. I don't have the math handy to prove it but I highly suspect that even a small change in the gap width will have a much larger change in the gap magnetic field strength.

I don't remember there being a simple ratio, but making the gap irregular causes non-linear distortion, though in a compression driver I doubt it's a mechanical issue, just increased VC heating. If the gap is narrower, then it can shift the frequency response lower with increased VC heating and vice versa, so tis better overall to increase the gap a tiny bit with proper tooling to make it uniform, clean, cooler running.

GM

[mah]

Inside shots: Field Coil conversion for JBL, Altec, and Western - diyAudio