Do you mean something like this:
Of course you'd need to adjust the values of the resistors according to your LOAD and what you put on the INPUT. The ground (GND or -) of the INPUT needs to be connected to the - of the BATTERY, otherwise it will not work.
You could also try the schematic below. It is more simple, but you will need a different transistor for it to work. The PN2222 you talked about is a NPN type. For this schematic you will need a PNP type. A PN2907 might work as some already mentioned, but it depends on your LOAD.
This might ask a little more current from your INPUT though. You also still need to calculate good values for the resistors.
So how to calculate what resistor values you need, and what schematic will work best for you? Wel, first we need more information from you, otherwise we/you can't calculate anything. What you need to tell us is this:
- What kind of load do you want to power? Is it a light bulb, or an LED, or a relay, or a small motor, or... And you need to tell us how much current will flow through the LOAD when you put 3V on it. If you don't know, we might be able to guess how much, depending on what it is :-)
- You need to tell us what's on the INPUT as well. Is it a battery, or a switch, or something else? How much current can be drawn from the INPUT? Because depending on the INPUT, the schematic might need to have some small adjustments.
It's probably not possible to create what you want with just one PN2222 that you already have. Unless your LOAD is something I didn't expect it to be... haha.
Edit: Added PNP variant and some extra info.
Edit: New information used to create schematic
You could try this:
I can't guarantee that it will work, because I don't know anything about your speaker, and you didn't answer how much current your RF module uses.