DIY 802 field coil drivers may be a reality!!

[BillWojo]

Thanks to Marshall directing me to the monster thread on field coil speakers on the DIYaudio forum, we may just have an option to "roll your own" 802 field coil drivers.
Here is the thread: Project Ryu - DIY Field Coil Loudspeaker - diyAudio
I spent many hours reading through this thread and came to the conclusion that although capable of the machine work necessary I was not capable of designing the electromagnet motor. So I posted a question to Hentai about possibly helping some Altec fans out with some design work and he said he would be happy to help. He is currently doing research on any conversions that he can find. He will need measurements I'm sure of the stock pot with the magnet removed.
I have two 808's, one has the cast pot and the other is a machined pot. The pot on the cast unit is about 3/16 of an inch longer. Cast pot is black with a 808-8A sticker on it, machined pot is green with a damaged sticker, 80? , last digit obscured. I assume it's an 808 as it's a good 3/8 longer in the pot than my 806's from my speakers. Can someone just verify this for me?
So if anyone has pics of both the cast pot and the machined pot without the magnet installed it would be a big help. Also anything on converted Altec drivers, actually anything on Altec field coil drivers, I want to load him up with as much documentation as I can.
This is very exciting, if you look through the post linked above you can see that this man is someone who would have been right at home in the WE labs in the early days. Today he has much more powerful tools at his disposal and is a dedicated field coil enthusiast.
I do believe we have been presented with quite an opportunity, let's do what we can to move this forward.

BillWojo

[norelco]

Altec field coil conversion - Field Coil conversion for JBL, Altec, and Western - diyAudio


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[BillWojo]

Thanks Norelco, they are great pics of an 515 conversion.
Have you seen Hentai's custom built drivers? Wow, in the early part of his design work he modeled the magnet structure in FEMM to optimize the magnet path in the structure. Found problems that he was able to design out before even making a chip.
I'll need to take one of these drivers apart and get full measurements to him. I'll wait to hear back as to what driver he wants to base it on.
The later all steel pots, are they machined from solid or is the end cap a weldment? (the end that bolts to the horn)
Also, having never opened one of these before, is there an easy way to get the plate off? The diaphragm cover screws hold the plate on, is the only thing left holding it the magnet? And yes, I know, once opened the magnet looses it's power. This is the reason I'm holding off to hear back from Hentai.

BillWojo

Hentai asked me if I knew what the alloy number of the steel is on the steel pot. Does anyone know where I can get that info?

[norelco]

@ BillWojo yes i've seen his work, the reason i subscribe to his thread because few months ago i visited a diyer guy who's doing customized / personalized tube amplifier and i get surprise that his using a fieldcoil 6.5 inch fostex driver for his demo tube amp. It sounds so good and seems like love at first sight/hearing the first time i audition the said speaker. From that day i start drooling around and searching for information about the field coil.

6.5 inch fostex fullrange speaker converted to fieldcoil with tube rectified power supply.




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[BillWojo]

That must have been a real treat to hear them. I have never heard field coils in a hifi application but have read enough to know that I want to.
I suggested the 808/802 drivers to Hentai because they are plentiful, not to expensive to purchase and I happen to have a crusty set. Actually, I have one cast pot and one steel pot. Once the decision is made as to what pot type to use, I'll be looking for a mate.
This is all very exciting.

BillWojo

[nullspace]

You'll want to make sure you touch base with Steve Schell before getting too far along; he's posted here and elsewhere on fundamental differences between the Lansing 801 & Altec 802, and what exactly is required to convert the 802 to field-coil operation. Hopefully he'll see the thread and chime in.

[BillWojo]

Thanks nullspace, I joined the Lansing Heritage forum and sent Steve a message. Hopefully he joins us. I see he has developed some very nice FC drivers but they are a different design altogether. Hopefully between Steve and Hentai we will come up with a design that is affordable for the average guy. Some of the FC drivers out there cost more than my whole system!

BillWojo

[lokie]

I am more interested in conversion of 15" drivers to field coil than the my 802's. The bandwidth covered by the 15"ers are much wider- 40hz to 2khz and cover the mid range... where the biggest benefit of field coil would effect.

Anyone have any direct experience w Jensen F15LL's? I am currently listening to Jensen's P15ll/s... the non-fieldcoil brother to the F15ll's. Wonderful driver!

Anyway... the F15ll's range widely in price.... anywhere from $300/ea to $1000/ea. Not sure why- anyone??

Would love to hear what people think of the other Jensen Field Coil's as well- M20 ($2-4k) /A12 ($200-$1000).

[Elitopus1]

I am more interested in conversion of 15" drivers to field coil than the my 802's. The bandwidth covered by the 15"ers are much wider- 40hz to 2khz and cover the mid range... where the biggest benefit of field coil would effect.

Anyone have any direct experience w Jensen F15LL's? I am currently listening to Jensen's P15ll/s... the non-fieldcoil brother to the F15ll's. Wonderful driver!

Anyway... the F15ll's range widely in price.... anywhere from $300/ea to $1000/ea. Not sure why- anyone??

Would love to hear what people think of the other Jensen Field Coil's as well- M20 ($2-4k) /A12 ($200-$1000).

If you want some Jensen A12's look out for old Hammond organs people are getting rid of. I have picked up two for free from Hammonds out for the trash.

[lokie]

If you want some Jensen A12's look out for old Hammond organs people are getting rid of. I have picked up two for free from Hammonds out for the trash.

What I "want" is information... How do they sound? Have you measured them?