Electronics > Beginners
Jellybean hobbyist general purpose transistors..
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bd139:
2n3055 is an interesting one. Modern ones are a lot better which means in some older kit the damn things oscillate violently. Have to stick a few pF across base/collector to make them shit again :)
Vtile:
But back in the day they used to handpick the 3-transistors used to every lunar lander and much details were given to select the right biasing currents for certain tolerance lot of transistors.  :D ...But I can bet that at least half of the writers on this topic do have hands-on experience on this particular thing and not just "I have read about this historic procedure" like me.
David Hess:
The 2N3773 is another ones of those parts which morphed from 0.2 MH to 4.0 MHz.

At one point Tektronix was using both the 0.3 and 0.8 MHz versions of the 2N3055 in the 76xx oscilloscopes and grading the 0.8 MHz parts for something (hfe or Ft?) to make 3 versions in the same product.  The 2.0+ MHz 2N3055s came later and I gather that they are the junk bin of TO-3 power transistors where other parts which meet the 2N3055 specifications but not their own get tossed.

I know of a couple times now where people had problems with oscillation in Tektronix high voltage inverters when replacing old and slow 2N3055s with fast modern ones.  Using a 2N3771G or 2N3772G which are 0.2 MHz or a 2N3055AG or MJ15015 which are 0.8 MHz solved it.  Tektronix changed something in their later inverters so they could use the 40 MHz D44H11 series (ring or perforated emitter transistor?) but I am not sure what, maybe the transformer?


--- Quote from: Vtile on October 16, 2017, 01:46:28 pm ---But back in the day they used to handpick the 3-transistors used to every lunar lander and much details were given to select the right biasing currents for certain tolerance lot of transistors.  :D ...But I can bet that at least half of the writers on this topic do have hands-on experience on this particular thing and not just "I have read about this historic procedure" like me.
--- End quote ---

In designs which rely on matching, trivial grading can be the difference between excellent performance and adequate performance or working and not working.  I try to avoid designs which rely on absolute specifications.
exe:

--- Quote from: floobydust on October 15, 2017, 09:23:11 pm ---I found TIP30's in my junkbox date code 1973. hFE measured 5. Tossed them in the garbage.
40+ years later, TIP30 still available and same specs. fT 3MHz, hFE 15-40, 30W.

--- End quote ---

That's how it supposed to be. Manufactures should not change specs for the same part number. Besides that, I'm not sure BJTs are evolved much last ~20 years.

Still, there are nice things like 2STA1942, MJE15028, BD139 (I like it because of low Vce(sat), there are smd equivalents). Use them, why using old junk?

EDIT: fixed typo
bd139:
bd139 ftw :)
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