[91] Transistors and Hfe

Date: April 23rd, 2008 | Comments : none | Categories: DIY.

2n4401 transistor hfe specifications

I frequently see talk on the forums about the HFE of a transistor. One thing to consider is that the HFE specifications on transistor datasheets are usually measured at much higher current levels than is found in the typical effects pedal.

Higher current usually equates to higher gain and the specs can be misleading. Take a look at the image above, which is from the datasheet of the common 2N4401 bipolar transistor.

At 150 ma. collector current (Ic), the HFE is 100 minimum, and as the current goes down, so does the gain. The typical booster or fuzz pedal is probably using the transistor at low currents – 1 ma. or less. This means the gain of 100 that you were expecting is more likely in the range of 20 or 30!


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