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Old 26th November 2005, 07:14 PM   #11
PB2 is offline PB2  United States
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Hi Chris,

That's a good point, there's a chance that parts from the same lot came from the same wafer where the silicon process is then identical. Parts from the same wafer should be nearly clones of one another.

Pete B.
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Old 27th November 2005, 03:42 PM   #12
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Thanks all for the ideas. I am going to order a few different sets. First the cheap 2n3055's to get it up and running. These should be pretty close to the BDY38's. I will get some MJ15003's and then some 2N3773's as well.

Thanks again and when it is up and running with these and new PS caps I will let you all know how it goes.
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Old 27th November 2005, 04:11 PM   #13
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Hi portlandlay,
The only thing to really watch is the speed of the outputs. Most are fast now and that's why I really like Pete's suggestion to use 2N3773's.

Replace the electrolytics on the boards before you start. Some of the film caps might be bad by now too. I would not use 2N3055's. Waste of time unless you have them. Be aware the original spec for collector emitter breakdown voltage is 60V, not 100V as many manuals state. You would need 2N3055H labled parts.

-Chris
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Old 27th November 2005, 05:00 PM   #14
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I think that the original BDY38 had a lower collector - emitter breakdown voltage (40 I think).

Since I am not at all a transistor educated guy which are the newer transistors that are too fast.

Also what would be the difference between the 2n3773 and Mj15003?

Regards

Stephen
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Old 27th November 2005, 05:13 PM   #15
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Hi Stephen,

Plug the different numbers in here to see the specs. I could just tell you, but this will allow you to look up the information yourself in the future. Just ask if you are unclear about anything.

-Chris
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Old 27th November 2005, 08:10 PM   #16
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Thanks - I printed out each of the data sheets. They are pretty similar and perhaps either is a good replacement. Both are certainly much better than the original BDY38.
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Old 28th November 2005, 10:14 PM   #17
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Hi Stephen,

The MJs are excellent parts but they're probably faster than the BDY38s, really even the 2N3773 is probably faster in todays technology but I doubt that you'll have a problem.

You might note the thermal resistance from the die to the package, which with all things equal is an indicator of die size. The 2N3773 is a bigger part than the 2N3055 which is also indicated by the higher power rating. It being high voltage will keep them out of secondary breakdown.

They're a preferred part indicating that they're going to keep on making them, probably because they're a superior substitute for so many of the older NPN TO3 devices. The larger die makes them slower which should offset the newer technology to some extent.

It is interesting that at a glance it might look like the 2N3055 has better hFE but you might notice that they're rated at different collector currents. The 3773 is tighter across temperature and higher across the more important 0 to 10 amp range as can be seen from the curves.

Matching is not an issue given that this is a quasi complementary design, but you probably don't want to risk any of the other parts failing and that's a good reason to change them all.

Pete B.

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Originally posted by portlandlay
Thanks - I printed out each of the data sheets. They are pretty similar and perhaps either is a good replacement. Both are certainly much better than the original BDY38.
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Old 28th November 2005, 10:49 PM   #18
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Just as you were writing this I was filling my order for 4 2N3773's.

I did notice (newbie here) that it is a little hard to make fair comparisons at a glance as many of the data sheets do quote specs apples to oranges or at least tangerines to oranges.

Thanks a million all for the replies. I have also order 4 new PS caps and a couple of other caps that look suspect. I will put this together and then ask more questions about setting bias.

The web page I quoted earlier does have a quick procedure - will the new transistors change this?

Regards,

Stephen
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Old 28th November 2005, 10:51 PM   #19
anatech is offline anatech  Canada
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Hi Stephen,
No, the instructions refer to the circuit. 2N3773's are the way to go here.

-Chris
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