Quick question about rating transistor gains

Started by kwijibo, November 03, 2011, 09:09:09 AM

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kwijibo

I've noticed it seems commonplace for people to cite current gain values for transistors as fixed values (i.e. transistor Y has a gain of X, Q1 in this fuzz pedal need a gain of 80-100). Whenever I've specified parts the small-signal current gain is always given against a range of Ic and Vce values. Is everyone assuming a standard bias current and Vce, or are people just repeating whatever comes up on their transistor tester/multimeter? I find it strange that so much attention is given to transistor gains when you can get a variety of values several times greater depending on how they're measured.

R.G.

I have practically made a profession of reminding people of that issue. I've posted it many, many times.
R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.

kwijibo

Quote from: R.G. on November 03, 2011, 10:29:49 AM
I have practically made a profession of reminding people of that issue. I've posted it many, many times.

:) Good to hear, it's nice to know I'm not totally confused or missing out on some secret information. This also explains why a lot of online "truths" about gain values in particular circuits don't always gel with my experience...

LucifersTrip

always think outside the box

PRR

> profession of reminding people of that issue.

How's the pay?

Do you have to be in the union?

> commonplace for people to cite current gain values for transistors as fixed values

Just look at the datasheet. hFE of a specific transistor may vary almost 2:1 over the range of typical currents. By over 2:1 over extreme temperature.

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R.G.

R.G.

In response to the questions in the forum - PCB Layout for Musical Effects is available from The Book Patch. Search "PCB Layout" and it ought to appear.