Video Polarity and Direct Injection

[old_coot88]

Originally Posted by vts1134

Can anyone verify that the circuit I posted should work? I can't get anything out of it.

You mean you've built it already? If it's not working, the transistor may not be biased correctly. First measure the emitter/base voltage, which should be about 0.7 V. If the voltage is too low or missing, you need to increase value of the base-to-ground resistor.

Or, if the emitter/base voltage is too high, the transistor will overconduct and saturate. So lower the voltage by increasing value of the base-to-12V resistor.

This is all assuming the transistor is NPN silicon type and supply is +12V.

BTW, the circuit shown will deliver only half the output level that it would if the non-inverting feature (which you don't need) were eliminated. The mod would be easy to do if the output level turns out to be inadequate. Here's a neat little tutorial on transistor biasing..
http://www.electronics-tutorials.ws/...r-biasing.html