Here is an idea from Chuck, W5USJ for an FET RF Gain Control...

"It's not optimum but it works a lot better than the direct-connected pot in the same place. It doesn't shut off completely because of the source to drain capacitance. Depending on supply voltage, the FET is pinched off at about 8 to 9 V on the drain. I asked Dave about other devices to do this job. He sez the one I used is pretty good and has much lower S/D capicitance than many others." 73, Chuck, W5USJ