[old_tv_nut]

You just need a much bigger capacitor. It should pass at least 30 Hz into 75 ohms, so
1/(2XpiX30xC) = 75 gives C= 70 microfarads. Use a 50 or 100 uFarad lytic, and put 100k resistor to ground to make sure it stays biased in the right direction. Reverse the lytic if the output of your device has negative DC (I'd guess not likely).

Edit: you didn't say if you removed the 75 ohm before attaching to your destination device. The destination should have 75 ohm input, so only use a 75 ohm resistor (across the 100 k ohm shown) for testing with a scope while not connected to a destination device.