[eschuen]

I was just told a transistor takes a signal and then send current to the control relay with 10 times the voltage. Where they implying a transistor can take 24 volt dc signal and make it 240 volts or does this only pertain to milivolts... confused as I know nothing about electronic systems

[donf]

If they were, I'd sure like to see a picture of one that can do that.

Yes, a transistor is a solid state amplifier, however, I believe the Voltage ranges are in the "Milli" (.001) volt range. It's been centuries since I've looked at design theory on transistors.

[Stratmando]

The current or voltage from Emitter to Collector is controlled by small voltage on the Base.
Use Op Amp and you can get a Million to 1 Gain, and very quiet due to Common Mode Rejection Rate. Anything common to both inputs is cancelled, with powerline noise or hum common to both, it is very quiet.
You can use a transistor to take a low voltage/current signal and control a higher voltage/current device.

[Mr_am]

Ya you can have high gain.. but never break the laws of physics.. Vout can not exceed Vcc. If you use a 9V battery you would never get an amplified signal whose amplitude is greater than 9V.

[KISS]

You guys, you all need to learn something:

Transistors use current to control current. It has current gain called Hfe.

FETS use voltage between the gate and source (Vgs) to control the current between the source, s, and drain d

See: Lecture Notes on BJT & FET Transitors v1.1.1

For a much better explanation

[Stratmando]

eschuen, about your question, You can use a Transistor as a switch or relay(in the fact you can control higher current with lower voltage).
SCR's are also handy, they have a latching feature, kind of cool.

[KISS]

Here is a datasheet on family of relay driver Integrated Circuits. Take a look at the equlivelent circuit for each channel.