I'm working on an IF amp and whatever I do it starts oscillating. A monolithic crystal filter 10.7 MHz, about 330 ohm is fed into a nicely designed npn transistor 20 dB amp, with bypass caps all over the sucker. It is in common emmiter configuration. The amp responds nicely to a test signal, but when I touch one end of the filter to the base, the amp starts oscillating at 10.7 MHz. I have to disconnect it from power to kill oscillation. I tried a simple L match, but has no affect. So somehow the amp is getting a positive feedback. Is there anyway to fix the problem?