02-22-2013, 01:18 PM
Thanks to everyone for your input. I've ordered a new 18 inch woofer, tweeter and 2-way crossover board from Parts Express. This weekend I'll see about getting some steel for coaxial mounting of the tweeter on the woofer. Later on, I'll order a suitable audio output transformer from Edcor, and get a metal box from somewhere to mount the crossover into, and the output transformer on.
The original speaker had a dual field coil - 680 ohms and 5000 ohms 8000 ohms (edit by me). From careful study of the schematic, it appears that the 8000 ohm section could be deleted as it served only to energize the original speaker. The 680 ohm section was used as part of the power supply. I didn't see any chokes from Edcor or Hammond with a DC resistance close to 680 ohms that could handle a fair amount of current.
E.H. Scott's model 800B originally used a 15 inch coaxial Jensen speaker, which had a dual field coil setup very similar to the MP VI. Later, this electrodynamic speaker was changed to PM. The PM replacement had a 680 ohm 675 ohm resistor mounted in back to replace the 675 ohm section of the field coil! And the 5000 ohm 9000 ohm section was deleted entirely. So...I'm thinking that, if it worked in the Scott 800B, that the same design should work in the MP VI...that is, using a power resistor to replace the 680 ohm field and eliminating the 5000 ohm 8000 ohm field.
I had actually bought a Scott 800B speaker for the McMurdo, only to find that it was the later PM type. I'll be reselling it as I really want an 18 inch speaker in my McMurdo. If I used a 15 inch speaker, I would have to mount it on a board to fill the empty space, then mount speaker and board inside the McMurdo.
You get the picture...
The original speaker had a dual field coil - 680 ohms and 5000 ohms 8000 ohms (edit by me). From careful study of the schematic, it appears that the 8000 ohm section could be deleted as it served only to energize the original speaker. The 680 ohm section was used as part of the power supply. I didn't see any chokes from Edcor or Hammond with a DC resistance close to 680 ohms that could handle a fair amount of current.
E.H. Scott's model 800B originally used a 15 inch coaxial Jensen speaker, which had a dual field coil setup very similar to the MP VI. Later, this electrodynamic speaker was changed to PM. The PM replacement had a 680 ohm 675 ohm resistor mounted in back to replace the 675 ohm section of the field coil! And the 5000 ohm 9000 ohm section was deleted entirely. So...I'm thinking that, if it worked in the Scott 800B, that the same design should work in the MP VI...that is, using a power resistor to replace the 680 ohm field and eliminating the 5000 ohm 8000 ohm field.
I had actually bought a Scott 800B speaker for the McMurdo, only to find that it was the later PM type. I'll be reselling it as I really want an 18 inch speaker in my McMurdo. If I used a 15 inch speaker, I would have to mount it on a board to fill the empty space, then mount speaker and board inside the McMurdo.
You get the picture...
--
Ron Ramirez
Ferdinand IN
