Author Topic: HFE tester on multimeters  (Read 3689 times)

onlymeeee

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HFE tester on multimeters
« on: February 09, 2009, 06:36:46 PM »
Hi,

I'm trying to test the HFE of some 2N3707s I have. 
I've put them into a multimeter (precision gold pg10B) observing the correct orientation according to the datasheet.  Put it to NPN.  The number just stays at 000. 

Am I doing something wrong?  Or is it that the multimeter is not capable of testing the 2N3707s?
Maybe it tests at too low a current for the transistors?


Rob Flinn

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Re: HFE tester on multimeters
« Reply #1 on: February 10, 2009, 11:11:58 AM »
I suspect that you have the orientation of the transistor wrong somehow.  The 2N3707 is a pretty standard transistor & I had no problems Hfe testing it with a really cheapy & nasty meter.
regards Rob

Capital letters.  The difference between helping your uncle Jack off his horse, & helping your uncle jack off his horse ........

toffifee

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Re: HFE tester on multimeters
« Reply #2 on: February 10, 2009, 11:25:47 AM »
Are you sure you inserted the transistor deep enough into the slots of the multimeter to make contact? I had this problem with my multimeter, I solved this by inserting three bare solid wires (for example cut from a resistor) into the slots deeply, then connecting the device under test to these wires.

Ptownkid

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Re: HFE tester on multimeters
« Reply #3 on: February 10, 2009, 11:59:56 AM »
Are you sure you inserted the transistor deep enough into the slots of the multimeter to make contact? I had this problem with my multimeter, I solved this by inserting three bare solid wires (for example cut from a resistor) into the slots deeply, then connecting the device under test to these wires.

+1

hitchhiker

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Re: HFE tester on multimeters
« Reply #4 on: February 10, 2009, 12:38:13 PM »
The other day I was having this same problem of a 000 reading on all my MPSA14 .


I tried them in every possible orientation but no work?

onlymeeee

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  • London
Re: HFE tester on multimeters
« Reply #5 on: February 10, 2009, 02:50:48 PM »
Are you sure you inserted the transistor deep enough into the slots of the multimeter to make contact? I had this problem with my multimeter, I solved this by inserting three bare solid wires (for example cut from a resistor) into the slots deeply, then connecting the device under test to these wires.

I have a feeling this is the case also but the lads won't push in any further without damaging the legs I reckon, so
Ill try the wire trick.  Cheers

desol

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Re: HFE tester on multimeters
« Reply #6 on: March 02, 2009, 12:47:40 PM »
I bought a cheap multimeter to test hfe...problem is, it doesn't test under the same conditions as what my 1290 would. Test conditions for the multimeter are: base current of 10uA and a Vce of 3v.

When i test, I get a value of say 14 for a transistor.

I need to figure out the math to convert this value, to the value it would be at the input stage of the B183av.

Neve chose the lead transistor for over 500-600hfe or something...and i'm trying some 109's and 107's and 184c's. I'd like to test all of them.

I'm thinking i need the B183av values, for a base current and typical Vce voltage, at the first stage under normal operating conditions, and eventually end up with a number i would multiply the '14' by...to get a number comparible to 500-600hfe.

The 1290 is 24dc...at 130mA..I think. But i have no idea what the values are at the transistor.

Anyone?

D.
« Last Edit: March 02, 2009, 02:42:06 PM by desol »

hitchhiker

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  • vancouver island,bc,canada
Re: HFE tester on multimeters
« Reply #7 on: March 02, 2009, 01:58:14 PM »
Can't help with your tester conversion but I think the above 600 is correct.
Most important on the first transistor in the amp stages.

PRR

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Re: HFE tester on multimeters
« Reply #8 on: March 03, 2009, 01:37:03 AM »
> a value of say 14 for a transistor.

"14" ? ? ?

"140" is more likely for ANY modern small transistor. Are you sure you are reading it right?

> the math to convert this value, to the value it would be at the input stage of the B183av.

There is no way to know. It may be a bit higher at higher voltage; but I doubt that stage runs 24V on the transistor. On small transistors, 10uA is "large" base current, and I bet your preamp runs much lower current. Hfe fall-off at low current is very process dependent.

Measure it in-circuit. Put a transistor socket in a preamp and try transistors.

Is this snippet like your plan?


If I found the right plan, Q1 runs near 250uA collector current. If Hfe were 500, then base current would be 0.5uA. Base current flows in a 68K resistor. 0.5uA in 68K is about 0.1V.

So measure the DC Volts across the 68K base resistor. If it is 0.1V or less, Hfe is 500 or more. If you really believe that maximum Hfe is somehow vital, go with the transistors which give the lowest voltage across the 68K.

Oh, and have a mike and speaker. A dead transistor may have very-very-low base current, but it's still dead.

thermionic

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Re: HFE tester on multimeters
« Reply #9 on: March 03, 2009, 06:42:45 AM »
Atlas Analyser

One of these will pay for itself in a matter of weeks, if not days. A very useful tool indeed.

Justin
Prepare yourself. You are about to become the voice of Interplanetary Parliament.


desol

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  • Calgary, AB
Re: HFE tester on multimeters
« Reply #10 on: March 03, 2009, 01:06:28 PM »
Crap. I had the pins going the wrong way. I thought i checked and double checked that??

I just got through testing a bunch of metal can bc109's. Out of 30, 11 were over 600, the rest less.
Most were 2-400.

Thanks for your answer PRR. To tell you the truth, i don't know whether it matters that much or not.
Probably not so much as other things matter, but...does that mean it doesn't matter at all?  ;)

Anyway, I always appreciate that i see you helping folks with things.

Cheers to all!
D.
« Last Edit: March 03, 2009, 02:00:25 PM by desol »

PRR

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Re: HFE tester on multimeters
« Reply #11 on: March 03, 2009, 03:32:14 PM »
> does that mean it doesn't matter at all?

It matters. In THIS circuit, Hfe under maybe 50 might  not bias correctly, Hfe of 100 would have a skoosh more hiss than Hfe=600. But Rupert himself could not hear 550 from 650. And 800 may not be measurably "better" than 600.

That's in the first stage. Later stages matter less. I'd like to use >200 there, and 800 would be fine, but 50 might work fine too.

> 11 were over 600

Put those in the first stage.

> Most were 2-400.

2 ? ? ? BC109 is supposed to be 200-800. That's at 2mA 5V. Your meter's 10uA base current in Hfe=200 will induce 2mA, and the 3V versus 5V is small difference.

Or were you meaning to type "200-400"? Then 100% over 200 and 36% over 600 seems about right for "200-800" specified parts.

desol

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Re: HFE tester on multimeters
« Reply #12 on: March 03, 2009, 05:33:29 PM »
- It matters. In THIS circuit, Hfe under maybe 50 might  not bias correctly, Hfe of 100 would have a skoosh more hiss than Hfe=600. But Rupert himself could not hear 550 from 650. And 800 may not be measurably "better" than 600.

That's in the first stage. Later stages matter less. I'd like to use >200 there, and 800 would be fine, but 50 might work fine too.



2 of the 30 were over 700hfe...but yes, i was thinking that anything over 550 would be reasonable for first stage. For second stage, I tested a bunch of metal can BC107 as well. These were from ST...whereas the BC109 were from Philips. Most BC107's were at 200-300hfe...with about 12 of 30 @ 350-450hfe. None over 500, but this may be normal for BC107?


- 2 ? ? ? BC109 is supposed to be 200-800.

Or were you meaning to type "200-400"?



Yes i meant to type 200-400. The more accurate the better.  ;D

Are there any real benefits to using transistors with metal can packages?

D.

« Last Edit: March 03, 2009, 05:41:24 PM by desol »

PRR

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Re: HFE tester on multimeters
« Reply #13 on: March 03, 2009, 07:09:00 PM »
> this may be normal for BC107?

Read the darn data-sheet! Some geek labored for a week to write it up.

http://newton.ex.ac.uk/teaching/CDHW/Electronics2/DataSheets/BC107_108_109_4.pdf

BC107 110-450
BC108 110-800
BC109 200-800

We infer that they come out of the oven anywhere from 100 to 1000, though mostly far inside that spread. The '07 bin gets the low-end, the '09 bin gets the high end, and when you order '08 you get whichever they have an excess of.

> Most BC107's were at 200-300hfe...with about 12 of 30 @ 350-450hfe. None over 500

Sounds like they have the oven tuned so it doesn't give many ~~110 parts, mostly over 200. And technically Hfe=451 is "reject" for the '07 bin, should be in the '09 bin. (If your meter found some Hfe=470 as '07, you could re-check at the specific test-conditions in the spec-sheet and see if they come out Hfe=449 or if you got a "reject". But you won't get money back unless you have thousands of mis-marked parts. And in fact the high-Hfe parts are more valuable for most audio uses.)

Note that if they finessed the oven to only yield 200-450, all three part-numbers could be sold from the same bin. Incidentally, there would be zero Hfe>600 parts... there is no promise you get any parts at the high end of the spread.

> Are there any real benefits to using transistors with metal can packages?

They look nice.

Someone may argue with me, but I thought it had been shown that epoxy is better in every way, including ways that just don't matter in shirt-sleeve studio work. (We used to think the metal gave a better seal, for oil-well, arctic, and rocket users.)


 

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