aluminum bobbins

[dazzlindino]

Hey gurus of all things ah.....pickuppy
Made a couple bobbins out of alum and wound them, read in the 7 ohm range at first but then they dropped down to a little under 3
Guessing that the alum electrons are influencing the coppers? Hmmmm
What could be used to shield the alum from interfering w the resistence?
Thanks

[David Schwab]

You cannot use metal bobbins. They will generate eddy currents and suck all the tone out of the pickup.

[dazzlindino]

Tone aside, why would the resistence change?
Or is that because of the eddie current?

[Sweetfinger]

Hey gurus of all things ah.....pickuppy
Made a couple bobbins out of alum and wound them, read in the 7 ohm range at first but then they dropped down to a little under 3
Guessing that the alum electrons are influencing the coppers? Hmmmm
What could be used to shield the alum from interfering w the resistence?
Thanks

You mean 7K ohms? Any change on that order, be it 7,000 to 3,000 ohms or 7 ohms to 3 ohms indicates to me that you've got a short in the coil, likely through the aluminum bobbin. Check to see if there's any resistance between the bobbin and either end of the coil.

[black_labb]

sounds like a short to bobbin. will make a very noisy pickup like that too if you dont ground the bobbin

[dazzlindino]

We all know 7 means 7K dont we?
Wound several Alum. bobbins : result is the same for all.

Then went and wound a couple dozen plastic bobbins with no such malady accuring.......same as last 10 years............

[Possum]

....

somewhere on your bobbin your wire is undercutting or is too tight against the metal and shorting to the metal. If you want to use them you need to wind with real light tension or tape insulate the bobbin before you wind it

[RedHouse]

...We all know 7 means 7K dont we?...

We who?

7 is seven, 7k is seven thousand, I'm sure we all know that ...don't we?

[dazzlindino]

somewhere on your bobbin your wire is undercutting or is too tight against the metal and shorting to the metal. If you want to use them you need to wind with real light tension or tape insulate the bobbin before you wind it

I guess that is possible, but have not had this happen on single coils where the wire is in direct contact with the slugs..


Anyhoo..... Im real dumb..so is 7k the same as 7K, or is there a difference?

[Dave Kerr]

Well shorts to the slugs would likely happen within the first hundred or so turns, so the impact on total DC resistance would be minimal. Any of the outer winds with a spot insulation failure could short out to a conductive bobbin.

[salvarsan]

Im real dumb..so is 7k the same as 7K, or is there a difference?

1. You're not dumb. You just need to learn a few facts.

2. Little k means kilo = 1000, as in kilometers km, kilograms kg, kilo-ohms kΩ, etc.

3. Big K means degrees Kelvin, as in liquid nitrogen boils at 77K and water boils at 373K.

-drh

ps. that ohms 'Omega' needs to be entered as "& #937;" but without the space.

[Rosewood]

Cover one bobbin all over in epoxy and give it another go.

[David Schwab]

ps. that ohms 'Omega' needs to be entered as "& #937;" but without the space.

So you can't do it like this? Ω (let's see if that worked)

I was wondering how you ended up with a symbol when it's not working for degree marks.

[edit] it did work, and I just typed option-z on the Mac... still no degree mark]

[RedHouse]

...You're not dumb....

Sorry, didn't meant it that way.

So you can't do it like this? Ω (let's see if that worked)

I was wondering how you ended up with a symbol when it's not working for degree marks.

[edit] it did work, and I just typed option-z on the Mac... still no degree mark]

Don't worry about it, in electronics you don't need to add the Omega symbol to denote Ohms, it's a given ...if... there is no multiplier symbol (K, M etc)

In a schematic, if it says "7" in a resistence measurement, it is automatically assumed it means Ohms because of the absence of a "specifier"

[David Schwab]

Don't worry about it, in electronics you don't need to add the Omega symbol to denote Ohms, it's a given ...if... there is no multiplier symbol (K, M etc)

Oh I know that. The reason I posted that was we noticed here that the forum wont do certain symbols, like the degree sign. I though it used to do it, but now you just get a question mark.

So I was surprised that Daniel got the omega to work.