Hello, This is a project I building now, a 180w an762 Motorola CCI amplifier I got off eBay built. I ordered a ptt rx-tx sense switch from Pacific Antenna qrp kits, then I'm using a ic-781 lpf from eBay,(seemed easier to work on with the schematic) with a rotary switch to provide 12v to open the lpf relay I want to use. 73 K9VPR