Electronics > Beginners
Jellybean hobbyist general purpose transistors..
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bd139:
Depends on what you're buying really and what for. If it's for hobby purposes, it's difficult to justify a 10-15x price multiplier on some parts for an assured supply chain. If you're building industrial or commercial electronics, then there's no question however.
Vtile:

--- Quote from: Cerebus on October 13, 2017, 12:31:30 am ---... and PN/MMBF4393 in most packages are easy to find and inexpensive. ...

--- End quote ---
Obsolete, according to Farnell :(
Cerebus:

--- Quote from: Vtile on October 14, 2017, 04:50:08 pm ---
--- Quote from: Cerebus on October 13, 2017, 12:31:30 am ---... and PN/MMBF4393 in most packages are easy to find and inexpensive. ...

--- End quote ---
Obsolete, according to Farnell :(

--- End quote ---

That's Farnell's odd way of saying we aren't stocking this any more.

Digikey have about 45,000 MMBF4393 on hand and about 1000 each of 2N4393 and PN4393. Looks like OnSemi are dropping the TO-92 packages soon, but there are lots of others out there who aren't e.g. PMBF4393 from NXP, marked active.

Never trust Farnell or RS's indications of part lifetime status.
T3sl4co1l:

--- Quote from: orolo on October 14, 2017, 09:59:33 am ---Sorry for going a bit off topic, but honestly, I'm confused beacuse this beta thing has been bothering me for a time. Do you mean that there is a workaround for low rout, or that it's not relevant for current sinks and active loads?

--- End quote ---

Degeneration was the key I mentioned.  Negative current feedback improves the constant-current-y-ness of the output.  It doesn't take much: a current mirror at 1mA (r_e ~= 26 ohms) benefits greatly from R_E = 100 ohms, while losing only 0.1V in saturation.


--- Quote ---Edit: Aha, I found it! What was spoiling the resistance of the current source was not the Va, but the choice of resistors R1 and R2. For high beta you need a much stiffer current at the base divider, m=100 or so. I think I'll need to think this over, much deeper.   :-+ Thanks!

--- End quote ---

Hmm, I'll have to think about that.

Does Vbe change much with respect to Vce?  I know that it does -- it's an oft-overlooked mode of operation of the BJT, and can be used for detecting saturation -- but I don't have a feel for how much, and if it's exaggerated for high hFE or not.  (I can imagine it might, as the base-thinning effect should act to increase r_bb' and Vbe.  This would also be consistent with Vbe falling in saturation.)

Tim
Vtile:
My go to list atm..

BC549/559 C-type, low-noise version of 547/557. Vcb is substantially lower though. I think I get them in 2(npn):1 relation. For those frontend project failures.  :-+ What about BC550/560 the noise figure seems to be specked even a bit lower, with same other specs.
PN2222/PN2907 For true general use, rather low beta compared to BC459, 2n2222 is a such a classic, comparable to ua741 and 1n4148 and PN-series is fraction of the price.
BD139/140 hmm...

Small amount of both
J113 as a general purpose JFET
MMBF4117 as for a toying around part

For a igfet, BS170/2N7000, seems to work with 5V logic, while not fully on, but usable. I need to search on the mosfets a bit more.

Anyone seen sot-23 to to-39 canning machine cheaply on chinese evilbays???  :D
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