[kheldar]

Hello,

does anyone know what a cheap multimeter is measuring on the built in transistor testing? Just for the heck of it, i tested the transistors I just got for a Gilmore Dynamic amp, and the PNP varied from about 230 to 280, and the NPN ones from 240 to 260. Does this tell me anything useful at all? or just that they are functional, and can I use this as a quick way to match transistors?

thanks

 

[tangent]

It was my understanding that they're measuring beta. (hfe) Does the meter's manual not talk about this?

 

[ppl]

Most Multimeters measure Bata as Tangent stated this is the gain of the transistor at DC under a constant current (See Meter Data Sheet) what your Data tells me is that you have quite a good match for a random selection of PNP/NPN Transistors. Yes you can use this to match transistors if your meter is a good one.

 

[kheldar]

heheh.. manual, thats good =) the manual for this multimeter consisted of the valid ranges of sensitivity for voltage, amperage, capacitence, and resistance.

Yes, the meter does lable it as HFE, but since its only a $15 meter, should I even bother with it for matching?

 

[tangent]

It's not hard to test for beta. If you trust it for voltage measurements, it should be good enough for beta measurements as well.

 

[alsq]

I bought two batches of 2SC1015 and 2SC1815 for
matching to build a gilmore, but my luck stinks.
I can match the 2SC1015 pretty well to each other,
with hfe in the 220 range. I can match the 2SC1815
pretty well to each other, but in the 150 range.
OK, OK, hfe should not usually be too important,
but I am unnerved by that delta hfe of 70 between
the PNP and NPN crowds.

What is that going to do to my Gilmore

?

Should I try to get another batch of 2SC1815 from a
different supplier (I bought all from MCM) and
hope in better luck?

Or should I altogether try substitute transistors?
If so, any suggestions on what type?

 

[tangent]

That's odd, the 1815s should be higher than the 1015s on average. It's normal for the PNP of a "complementary pair" to be inferior in most respects. You have the opposite situation.

A good amp design doesn't depend on Hfe, though, so quite possibly the difference won't matter. I certainly wouldn't worry about it if you just got the numbers backwards, since that kind of difference should have been counted on.

 

[alsq]

Unfortunately the numbers are correct, and that
got me puzzled too. On the 1815 side the uniformity is
impressive, I could have picked any six in the batch
and they would have had the same hfe plus or
minus five. On the 1015, it was a bit wider
(plus fifty, minus fifteen) but still pretty homogeneous.
Batch size was not large (twenty-five samples).

The voltage measurements on KG's rig are out of
specs from what KG published, but are in line with
what most other people are getting, too.

Maybe it's time to think about substitutes? Prices
dropped since KG ordered his transistors (they're
about one-fourth the cost), but specs seems to
be on average rather different.

 

[Arzela]

Are they of the same grade?
I'd guess not. I have plenty
of these things. Feel free to pm
me if you'd like to arrange a possible
trade.

 

[Tuomaster]

My problem is that I have too good NPN:s. Well..I won't let that bother me anymore and I'm finally soldering this amp together. If it doesn't work, it doesn't work ;p

hFE values:
2SC1815 410-430
2SA1015 160-250

 

[kheldar]

i know its a dumb question, but i ask because i just realized i did this, are you sure you have the leads going in the right holes in your test board/multimeter?

I tested some fets for a meta42 im building and was getting 400-500 ranges, until i realised i hade them in the wrong test position... retesting them gave me values in the 180-250 range

my bad, but at least i learned to double check my spec sheets =)

 

[Tuomaster]

Quote:

Originally posted by kheldar i know its a dumb question, but i ask because i just realized i did this, are you sure you have the leads going in the right holes in your test board/multimeter?

Yes, I'm sure. Those NPNs are BL-grade and PNPs "only" GR.

 

[JohnFerrier]

Quote:

Originally posted by kheldar Yes, the meter does lable it as HFE, but since its only a $15 meter, should I even bother with it for matching?

You will need to try it to see for yourself. The meter many not have super absolute accuracy. However, what works in your favor is that for matching, you will be making relative measurements. So, however inaccurate a reading is for one transistor it will be off about the same for the next transistor. For example, even if the reading is 1%-2% off, it is off about the same 1%-2% for a comparative measurement. (Also, I read that FETs are heat sensitive and should be handled with tweezers. Don't know if you will notice a tempco with the transistors...).


JF