How to Find Substitutes for Discontinued Transistors
As promised in the Fisher RS-2010 video series, here is my attempt at showing how to find substitute transistors when the original is not available. This problem presented itself when we tried to order the components for the STK discrete component modules used in the video. In this video, I go through the process of finding a replacement for the NJW3281 transistor. The same process can be used for other transistors. As you will see, I actually found another source for the original NJW3281, as well as some alternates.
Hi Tony. There is a mistake on that transistor name diagram that you showed. The TO-3P(L) is not the same as TO-247. The TO-247 is simillar in size to the TO-3P(N), it just has the front fully covered in plastic. The TO-3P(L) is actually a TO-264. The transistor that you showed as an example, MJL21194G is a TO-264 and the MJW21194G is the TO-247 version.
~BRILLIANT~~~
great video. a note on power semiconductor maximum power rating: most often the Pmax is determined at Tc (Case temperature) at 25C, and it must be derated if the transistor is running at +75C case temperature an example Onsemi mjl3281a Pmax at ta 25c =200W , derate 1.43W/C, leaving only (200-71.5W) =128.5W or at Tc 125C (200-143W) = 57W .
matching of power transistors is ususlly done at a specific collector or base current, : have a metal object such as a 3 ounce aluminium tile on table or in a vice, against what you press the transistors during the HFE measurement (5-10W dissipation would burn your finger in pretty short time) , pick 20 MJL1302A PNP and 20 MJL3281A NPN transistors, (look smallest current for hfe measurement from datasheet (1A and 5V) feed constant current of say 13mA to base use current limited lab power supply set at 5V 2A and measure collector current, take 2 suitable binning item such as carton for 12 eggs you might like to mark the cartons for NPN and PNP) my practice is to use black or blue for NPN and Red for PNP ), and mark each collector current to the carton. reverse polarity of power supply and base constant current source, and repeat with the PNP transistors. Greetings from one who once worked as Semiconductor manufacturer Field Applications Engineer .
Integrated amplifier modules? It’s not much different with tube Substitute handbooks.