voltage-divider bias
How do you set the transistor's resting current so it stays put, even though beta is all over the place and drifts with temperature? The trusted answer is voltage-divider bias: pin the base at a fixed, stiff voltage with two resistors, and let an emitter resistor set the current. It is the standard, textbook-correct way to bias a single-transistor amplifier, and it is wonderfully indifferent to the exact value of beta.
Here is the recipe in four resistors. Two resistors (R1 from the supply to the base, R2 from the base to ground) form a voltage divider that holds the base at a steady voltage. An emitter resistor (Re) sits between the emitter and ground, and a collector resistor (Rc) sits between the supply and the collector. Walk the numbers: with a 12 V supply, R1 = 47 kohm and R2 = 10 kohm put the base at 12 times 10/(47+10) = about 2.1 V. The emitter sits one base-emitter drop below that, 2.1 - 0.7 = 1.4 V. With an emitter resistor of 1.4 kohm, the emitter current is 1.4 V / 1.4 kohm = 1 mA — and the collector current is essentially the same 1 mA. Notice what just happened: beta never appeared in that calculation.
That is the whole point. Because the base voltage is held firm by the divider, the emitter resistor fixes the current by Ohm's law, not by beta. If beta is 100 or 300, if the part warms up, the current barely moves. The one rule to respect: the divider must be "stiff" relative to the base current — make the current through R1 and R2 roughly ten times the base current, so the base loading does not droop the divider. Voltage-divider bias is the reason a mass-produced amplifier works the same with any transistor you solder in.
Take that same circuit and swap the transistor for one with beta 300 instead of 100. The base voltage is still 2.1 V (the stiff divider does not care), the emitter is still 1.4 V, and the current is still 1 mA. Compare with a single base resistor, where tripling beta would triple the current and shove the amplifier into saturation.
The same bias works for any beta — that is what makes it production-worthy.
Voltage-divider bias only buys stability when there is an emitter resistor. The divider holds the base voltage; the emitter resistor turns that into a stable current. Omit the emitter resistor and you are back to depending on beta.