How Are "Henries" Measured?

[Mystic]

Isn't Henry the guy that messed up Gibson?
It's Saturday and I had to work.....

[Possum]

cheap inductance

the cheap multimeters aren't good for inductance readings at all. They have autoswitching from 120-1Khz. My Meterman 37xr does this and it fails miserably at reading guitar pickups in the 1khz range, it will hit around 4 henries then read OT and switch to 120H, totally useless for guitar pickups. I had the damn thing for a year and when I got the Extech found out most of my readings weren't very accurate at all. The Extech is pretty much the ONLY small LCR meter that works for guitar pickups. Multimeters with inductance add ons don't work right. Bill Lawrence is another guy who uses the Extech you can see it pictured in his ad in VG. LCR readings are useful but unless you buy a super expensive HP LCR meter that reads also at 10khz, you really don't get the full picture of whats going on in the coil. Useful it is though...

[David Schwab]

Isn't Henry the guy that messed up Gibson?

Yeah, and he also messed up Opcode, and Oberheim, and Steinberger, and Tobias, and....

[Sweetfinger]

Got my Victor LCR Meter!

The booklet says it measures up to 2H using 150uA current @ 1Khz, 20 Henries using 15uA @ 100 Hz.

I measured some common household items:

red reissue Fasel inductor--------- 638 mH
dunlop black inductor------------- 585 mH
old organ inductor stamped 500mh-508 mH
'75 Jazz Bass pickup, 7.5K---------- 6.2 H
recent mex strat pup w/steel poles-- 7.0 H
Duncan screamin demon trembucker- 9.2 H
some kinda Tele rhythm, alnico------ 5.4 H
10" alnico 8 ohm speaker------------ 0.7 mH and beeped
Valco 2X 6L6 OP Xformer, open secondary was 10.4 H and with secondary connected to 8 Ohm load, measured 3.95 H.

Do these readings seem correct? The wah inductors seemed right on.

[soundmasterg]

You'll notice it says it measures only up to 2H @ 1000 Hz. That isn't high enough as even your lowly Strat pickups are about 2.2 henries. Every one of those pickups measured is off from where it should be and is much too high. Even a run of the mill P90 is going to be about 4.5 henries, and based on what you posted so far I bet your meter would say it was more like 10 henries. Take a look at the Extech 380193 specs at this site.


http://www.tequipment.net/Extech380193.asp

[Joe Gwinn]

Most LCR meters cannot measure pickup inductance correctly

The booklet says it measures up to 2H using 150uA current @ 1Khz, 20 Henries using 15uA @ 100 Hz.

I measured some common household items:

red reissue Fasel inductor--------- 638 mH
dunlop black inductor------------- 585 mH
old organ inductor stamped 500mh-508 mH
'75 Jazz Bass pickup, 7.5K---------- 6.2 H
recent mex strat pup w/steel poles-- 7.0 H
Duncan screamin demon trembucker- 9.2 H
some kinda Tele rhythm, alnico------ 5.4 H
10" alnico 8 ohm speaker------------ 0.7 mH and beeped
Valco 2X 6L6 OP Xformer, open secondary was 10.4 H and with secondary connected to 8 Ohm load, measured 3.95 H.

Do these readings seem correct? The wah inductors seemed right on.

The inductor values are probably correct, but I would be very suspicious of the pickup values.

Aside from the test frequency switching from 1 KHz to 120 Hz right in the middle of the inductance range of real pickups, there is a deeper problem: Most handheld LCR meters are designed to measure fairly "pure" inductances only, but pickups are not at all pure, having a fairly high resistance for their inductance, causing many LCR meters to be wildly off.

A good test is to take one of the relatively pure inductances (such as the inductors listed above) and wire a pot in series, and measure the inductance of the combination. Does the indicated "inductance" vary by much as the resistance is increased? If yes, measuring pickups with that LCR meter simply won't work.

If one is energetic, one can also build a Maxwell-Wein Impedance Bridge (http://home.comcast.net/~joegwinn/), which is what was used to validate the Extech measurements. This is the acid test, and can be used for any frequency, not being limited to 1 KHz and 120 Hz.

So far, the only ~$200 handheld LCR meter that is proven to work with guitar pickups is the Extech 380193, which is fast becoming the industry standard. The standard test frequency for pickups is 1 KHz; the 120 Hz is for power-supply components.

[Sweetfinger]

I'm still happy

I will probably use the Victor more for ID of wah inductors and power supply chokes, anyway.

The link for the Joe Gwinn bridge is not working for me. Fresh link anyone?

[Joe Gwinn]

The link for the Joe Gwinn bridge is not working for me. Fresh link anyone?

The URL is correct, but the trailing slash parens confused it. It turns out it needs the url tag and antitag.

Try http://home.comcast.net/~joegwinn/.