if you understand the circuit, test your legs to select a new part and see how it works. If you don't have a clue, try to get the exact replacement part. To properly answer this question involves understanding the circuit design. The obvious parameters to satisfy are breakdown or max collector voltage, next is beta (hfe), finally for more specialized applications noise, or gain bandwidth. Just like you can replace a bolt with a stronger bolt, your can replace a transistor with a stronger (better) part 99% of the time. A low voltage low current GP device, and higher voltage GP parts, and very low noise parts for preamp front ends. I still have hundreds of the 3 legged buggers sitting in my back lab. In circuit design there are (were?) many transistor applications where a design engineer used the GP NPN or PNP device that he already has in stock. The rules for substituting is pretty much the same as the rules for initially selecting transistors, while it's a little like replacing nuts and bolts in a car, you want the replacement to be strong enough and fit in the hole. Is there a general rule for value deviance (I'm thinking hFE and power dissipation: if higher no problem?) or does it exclusively depend on the circuit the transistor is used in? Abstract: bd139 equivalent transistor equivalent book 2SC2073 2N3055. However, even if I had the schematics, I still wouldn't really know how to find close enough substitutes. TRANSISTOR REPLACEMENT GUIDE Datasheets Context Search 2001 - MJ3001 equivalent. I haven't been able to source a free copy of the schematics yet, so not sure exactly what the transistors do, but I thought I might give it a try anyway. Most of the transistors I'm looking for are designated as "general purpose", used in the (motor) control section of an old CD player (i.e., 2SA933 = 2SA733, 2SA970, BC556 - so probably all fine).īut there are a few I can't find equivalent matches for that look close enough. A quick search on the net gave me these pages. I need to replace a few obsolete transistors.
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