Hoffman Amplifiers Tube Amplifier Forum
Other Stuff => Cabinets-Speakers => Topic started by: Dave on November 21, 2025, 07:54:23 am
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Hi guys,
So, I come across Hammond organs occasionally and I take them in and get them working well and then return them to the wild. Once in a while I get one that is beyond repair and I cannibalize it for parts to use on other ones.
Recently, I obtained an organ (not hammond) that was beyond help and gutted it for parts. It had a strange (to me) rotating speaker arrangement in it.
It was a device shaped like a war hammer with a drive shaft in the middle.
On the business end was a drum with two 3 inch tweeters in it and on the other end was an adjustable counter weight. The speakers were shot and the motor was dead, but it looked interesting to play with.
I scrounged up a couple of full range car audio speakers that would fit to experiment with. And repurposed an old tone wheel motor to get it going. Adjusted things so that it would spin at 400 RPM's and gave it a whirl.
Wow, I was shocked at how cool it sounded.
Here's the rub. I don't understand how it is coupled to the amplifier.
On the drive shaft there is a stationary doughnut shaped coil of copper wire that looks like an inductor. Inside that and attached to the moving drive shaft is another one. The two don't make physical contact. One spins inside the other.
So, I guess that this is capacitively coupled?
How would one work out a crossover for such a thing?
Dave
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stationary doughnut shaped coil of copper wire that looks like an inductor. Inside that and attached to the moving drive shaft is another one.
guess that this is capacitively coupled?
sounds like inductive coupling, the stationary side I would guess is the secondary or speaker side
How would one work out a crossover for such a thing
I'd probably just wire it in parallel with a bass speaker n let the ear decide, otherwise start with just an off-the-shelf X-over
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sounds like inductive coupling, the stationary side I would guess is the secondary or speaker side
How would one work out a crossover for such a thing
I'd probably just wire it in parallel with a bass speaker n let the ear decide, otherwise start with just an off-the-shelf X-over
The inductors are the other way around.
Wouldn't the inductors have to have a mechanical connection for it to be inductively coupled? I thought maybe there was capacitance going on between the two "inductors". Yeah, that's what I don't get.
Either way, it works like a champ. "Ear decide" sounds like the way to go.
Dave
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Wouldn't the inductors have to have a mechanical connection for it to be inductively coupled?
no, think of the "core" being "air" when you induce a current in one coil, the second coil will "couple" the signal "over-the-air" (through the magnetic flux created by the current flowing through the primary). the air-gap, IIRC has a "capacitive" effect
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Thanks for that. It gives me something to think about.
Dave
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Are you sure this is not just a simple slipring assembly? If you connect an ohm meter to the red and/or yellow gator clip leads, can you read continuity (zero ohms) to the actual speaker wires?
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Are you sure this is not just a simple slipring assembly? If you connect an ohm meter to the red and/or yellow gator clip leads, can you read continuity (zero ohms) to the actual speaker wires?
I'm as sure as Doxidan. As sure as the sun rises. No continuity. I wish there was. It would make things a lot more simple.
Dave
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gives me something to think about.
Once that's out of the way, do the math, if that doesn't kill curiosity, I don't know what will! :icon_biggrin: