Pinging Bruce Griffing, transistor question

[rockrat]

Well, I have survived the first 2 weeks of my new job and I'm getting things back to normal at home. I think... Found a switch for my tig foot control and a capacitor for the TV that released the important blue smoke. Tried lighting a cig and blowing the smoke back in to the TV, but I cant keep it in there long enough to plug it back in. http://bbs.homeshopmachinist.net//biggrin.gif

Bruce, back in the thread
http://bbs.homeshopmachinist.net//Forum1/HTML/013345.html
we were talking about replacement transistors. I have been kicking this thought around a bit. You had mentioned a couple of things that got me thinking.

1) You had found a cross-ref for transistors that worked on the internet, but didn’t mention what site it was on. Do you still have that link? NTE has a cross-ref for their stuff online at
http://nte01.nteinc.com/nte/NTExRefSemiProd.nsf/$$Search?OpenForm
Kinda handy.

2) I found a transistor that NTE makes which they claim is a direct replacement for the DTS411. There are some differences in the NTE and your suggesting and I'm not sure if they make a difference. Here are the specs copied from pdf into a jpg.
http://i4.photobucket.com/albums/y128/katiecat222/transistor.jpg

The NTE is in a TO3 package which is nice. But for the few bucks I would save using your suggestion, I can make them work. Might need to add a heat sink and worst.

How do these specs differ and how will they make a difference in the design? Thoughts?

Thanks rock-

[Bruce Griffing]

The transistor I suggested has the appropriate voltage and current ratings, but it is a darlington pair. For that reason it has more current gain and has a higher effective base emitter voltage. The reason I suggested it is that the original transistor has a pretty high current gain (called beta or Hfe). It was easier to find a cheap darlington than anything else. The chance that it will work in your driver circuit are very high, but not 100%. As I said - it would be the one I would try - just because of the cost. As to the case, I assume your current TO3 devices are already mounted on a heat sink or at least a large plate. I would do the same with the substitute device. It should work fine. If you have schematics or a reference to schematics, I could give you a yea or nea on the substitute.