Summarised_solution:
General purpose high current, high gain SOT23 bipolar & MOSFET transistors are available at modest cost. These will work if the part is used as an on/off saturated switch and will probably work in other roles.
Required polarity can be determined by a single measurement.
SOT23 small signal transistor is usually -
b c e for bipolar
g d s for MOSFET
as per diagram below.
Measure voltage 2 to 3.
If 2 is +ve wrt 3 then = npn or n channel.
If reversed then pnp or p channel.
A high current high beta npn or pnp will work in most bipolar cases.
BC817-30 / BC807-40 are good.
-40 means AVERAG current gan of 400. ie 250-600 range.
50V, 800 mA rated for thisFairchild example sold by Digikey
Rbase of 1k to 10k should be OK.
MOSFET N Channel needs low Vgsth.
CES2310 utterly superb if you can get them.
OR
36 cents /1 in stok at Digikey for this
2.6v Vgsth , 60V, 1.A continuous
IRLML2060
But, Better! -->
INFINEON BSS205 N !!!
20v, 2.5A, < 100 mohm Rdson at 2.5V Vgs.
In stock Digikey 37 CENTS /1
No gate resistor needed. Use say 1K if desired.
For P Channel use Digikey selector guide to select out specs of chouce then sort by price ascending in quantity 1.
This is a truly marvellous part for amateur general use.
Be ware of 20V Vds max but otherwise marvellous.
eg 0.2V Vds at 1.5A at 2V Vgs.
500 mW disispation and 250 K/W mean due care needed thermally (as in all SOT23)
BUT very low Rdson will keep it OK in many cases.
eg 98% of these have < 80 milliohm Rdson at high temperature.
At say 1A dissipation <= 80 mW for 20 C case rise on modest copper.
If you MUST have 30V there is the very nice 41cents/1
IRLML6346
Dynamic range refers to the difference between the maximum signal a system can handle and the noise floor for a specific system configuration. If the gain of the system is fixed, there is no difficulty with this definition. If the gain of the system can be varied, then the dynamic range becomes a function of the system gain. The use of the word "dynamic" means that it refers to the system capability in processing a signal at one point in time, in other words for one specific gain. Since the gain can only be varied statically, you cannot claim increased dynamic range by having a variable gain. For example, if you have a 10-bit A/D converter in the system, the dynamic range is generally taken as approximately 6 dB X the number of bits or 60 dB in this case. If you put a variable gain amplifier (say with 0 to 40 dB gain in front of this A/D converter, you can't claim the dynamic range of the system is increased by 40 dB. The advantage of the variable gain amplifier is the ability to set the system dynamic range over a given voltage range. For example, if the maximum input of the A/D converter is 10 volts, then the dynamic range of the system with the variable gain amplifier can be shifted from 10 millivolts to 10 volts with the amplifier gain set to 0 dB, to 0.1 millivolts to 100 millivolts with the amplifier gain set to 40 dB. In both cases, the dynamic range remains at 60 dB but the static range has increased to 100 dB.
Best Answer
It is a mouth-full to say as a full name. I found this description here.
EDIT: When I talk about transistor gain with other engineer's, we often use the term 'beta', yet in a datasheet 'hFE' is normally what is used by the manufacture based on calibrated equipment for a standalone transistor.
For some transistors hFE readings may be done at several crucial frequencies as well as DC. 'Beta' is a better term for common-base designs, or just a general statement about DC and/or AC current gain in a known circuit.
As a refinement of the original answer, @carloc mentioned that a 'hFE' spelling refers to a DC signal of relatively large amplitude, while 'hfe' refers to a small signal measured deferentially around some common bias point. No specific thresholds were given, though my original answer refers to 'hFE', the DC gain of the transistor.