What current and amperage needs to be supplied to the base of a transistor, is it possible to control an 8 amp

Question

supply with 6ma applied to the base, is .7v a rule of thumb if so, how do i calculated the actual voltage needed?

Answer 1

8 amp divided by 6ma is 1300.

It's current that controls, not voltage.

Transistor gains do not go that high (1300)

Even darlingtons have trouble, but you may be able to find one with a combined gain of the two stages equal to that number, although you need at least gain of 2000 if you want saturation.

Darlingtons are two stages cascaded, so you need about 1.4 volts on the base.

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Answer 2

Since you'd need a current gain of over 1000, I don't think a single conventional bipolar transistor would do it, but a darlington pair might (which may well be fabricated as single device) should work. Or a power MOSFET might be used.

The voltage depends on how the circuit is configured, for a common emitter configuration, it is about the base-emitter voltage of the transistor, for silicon about 0.7V, but a darlington has two base-emitter junctions in series, so about 1.4V, but actually it will have to be a little higher for saturation, it varies a little, check the data sheet for the transistor you are using.

For common-collector is it a little more complicated.