Measure a choke

[Reeltarded]

Who is Henry, and how do I find him?

What do you read inductance with? I have some chokes that I think are 3, 5, 10, and 20h but not sure what to look for.. or at them with.

Imma monkey!

[martin manning]

That would be Joe Henry, but he passed away in 1878. The quick and easy way is to get an LCR meter, but you can also rig up a little test using an AC signal and a pot and use a regular DMM.

[Reeltarded]

Well, he gets a lot more press than Kelvin, still.

Thanks, Martin. I will mess around until I think I know what I am doing, as usual.

[Phil_S]

I think I got this from someone at AX84. Seems to be simple and cheap.

It beats the heck out of buying a real LC meter, which will set you back at least a couple $hundred or more. The cheapo hand held ones -- I'm told they don't report accurately for the kind of choke we use in guitar amps. Ours are way bigger.

[Reeltarded]

I am a tauist. I will just use L=R/(τ*Freq)

Thanks, Phil!

[tsutt]

And how much does a var. freq generator cost or ?

[Cygnus X1]

And how much does a var. freq generator cost or ?

I bought a Hewlett Packard 3312A Function Generator for $50.00.
Does that count?
It seems to generate a lot of frequencies I can't even imagine using.

My dog hears some of them and it's funny to watch her head go twisty-turny.

http://circuitslab.case.edu/manuals/Hew ... Manual.pdf

[Phil_S]

I loaded a freeware program on a very old but still functional laptop. AFAIK, it should work fine. I bought a thingy (technical term) to plug into the headphone jack that will let me plug in a guitar cable -- About $2 on ebait all the way from China, I'm pretty sure. I'm not sure if I'll need a way to step up the signal or not. I am guessing I can figure it out. I have an old stereo amp I can use to boost the signal. Of course, that throws out the thingy. I'll have to rig up a guitar cable to the speaker jack on the stereo.

I asked before, but don't remember. What is the voltage of a typical guitar signal? What is voltage output on the headphone jack of a computer with the volume maxed?

My intent was to use it with a scope.

For the inductor testing, I think whatever comes out of the computer will work fine.

[Reeltarded]

I think ya plan on mean averages of 1v output to ballpark it. Strats do itty bitty voltages and an angry Tele bridge pickup can knock on that 1v I bet.

As I recall some older laptops use the headphone out as audio output so as far as matching there.. you might be better Googling your hardware to find out what it takes to zero that sucker.

[martin manning]

No need for a function generator... Here's another take on the same basic idea for measuring inductance that can be accomplished using a filament transformer as the AC source. Miles, this ought to work just fine for sorting your chokes.

[Reeltarded]

Oh good. I can just power it off my freak Communication Breakdown amp with messed up heater voltage. Should be about right.

[Phil_S]

Martin: Please clarify:

"r" is simply the measured DCR of the choke? Not an additional resistor placed in the circuit. Is that right?

How is "R" selected? The example is 1K. Is that arbitrary? Is there a relevant range? I see it forms a voltage divider with the choke, so I'm thinking it should not be too much larger than the DCR of the choke?

When building, the schematic indicates one side of Vs is grounded. Also, one end of R is grounded. Do we simply connect the ground side of R to Vs? If so, there is no ground reference and is that important? Does this circuit actually need a metal chassis, with a transformer and a chassis ground? Or can/should ground simply be a terminal strip lug that isn't connected to anything?

I am thinking I can build this on a block of wood with a terminal strip, but no ground will be present, at least as I understand ground.

I am sorry to be so dense about this, but 1) I want to be safe, and 2) I want it to work. As you may have guessed, I have a couple of unknown chokes, too.

I am having trouble wrapping my mind around the fact that I've got 2 leads from the 6.3VAC transformer and what to do with the side for which ground is shown.

Thanks.

Phil

[Reeltarded]

"r" is simply the measured DCR of the choke? Not an additional resistor placed in the circuit. Is that right?

Yes

How is "R" selected? The example is 1K. Is that arbitrary? Is there a relevant range? I see it forms a voltage divider with the choke, so I'm thinking it should not be too much larger than the DCR of the choke?

I don't think the value matters so much as a range for the calculation. 1 is an easy number to work with and 1 factored some keeps the decimal in an easy place?

When building, the schematic indicates one side of Vs is grounded. Also, one end of R is grounded. Do we simply connect the ground side of R to Vs? If so, there is no ground reference and is that important? Does this circuit actually need a metal chassis, with a transformer and a chassis ground? Or can/should ground simply be a terminal strip lug that isn't connected to anything?

Say you have a board with a terminal strip with the ground wire from your wall power on a lug and the + on another. R shares ground with VS.

I am thinking I can build this on a block of wood with a terminal strip, but no ground will be present, at least as I understand ground.

Yes it will be present on the ground lug where your service terminates to the ground leg of your power supply.

I am having trouble wrapping my mind around the fact that I've got 2 leads from the 6.3VAC transformer and what to do with the side for which ground is shown.

That ground goes to the ground from the wall. (On a lug) there is no phase + common, just a simple lamp cord could work.

I could be totally wrong, but I think I am not and if I don't practice talking about it who'd ever know.. so I do.

To add; these little circuits are confusing because we are used to looking at blocks of them that work together, I say. This circuit looks really ugly on your bench, huh? heh

[Phil_S]

Miles:
The shame of finding one's self stuck inside the box! I did not imagine a 2 wire lamp cord and did not think of the neutral as ground, which of course it is. (The green wire on a 3-prong is simply the redundant neutral.) Of course, I've got a suicide cord on the filament transformer (plugged into a power strip with a breaker). I just need to tie this butt ugly circuit into the neutral side of the wall feed? Wow, look what you are making me do. I need to find a suicide cord with a polarized plug! Thanks.
Phil

[Reeltarded]

Low voltage.. we could even use wall warts with a little snipping. Probably the easy way even.