One of the final things I need to work on is optimizing the muting of my receivers during transmit. I currently have a control box with relays inside that plugs into the back of my HB transmitter cabinet. I used it years ago to mute my 3 National receivers at my old station back in Tulsa. The box also contains 8-ohm load resistors the receivers output to during transmit. Basically I tried muting the HRO receivers and/or the NC-183D by their normal muting method first which basically turned the B+ off. Unfortunately that led to very loud speaker feedback and popping before and after mute happened so I added the 8-ohm resistors with a slight delay to the other B+ on/off relays to eliminate it by disconnecting the speakers first, etc. However, every time I went back to receive the receivers had drifted some. I soon realized it was a very bad idea to shut the B+ off in the old tube receivers during transmit. Even if it doesn't shut off the VR tube going to the oscillator tube's screen many components still have to warm back up again each time. Nowadays I'm just using the relays to switch to the 8-ohm load resistors then back to the speakers and I'm no longer muting anything else. I'm using the simple protection circuit attached below mounted at the receiver output connector inside of my HB antenna coupler which contains a large vacuum T/R relay. This prevents any large RF dumps from getting to the receivers during transmit across the open T/R relay contacts. Anyway, my goal is to try and eventually eliminate all mechanical relays at my station except for the main vacuum T/R relay inside of the antenna coupler. The problem is they would need to be SPDT and not SPST to disconnect the speakers like I am currently doing. I could maybe use SPST solid state relay bricks to externally control the CPC1788 relays Jim referenced in another topic instead, but I want to keep it simple. Maybe lift the AF tube cathode connection and short the 1st IF tube's grid input to ground or something similar during transmit. Basically I want no speaker noise or frequency drift to occur and shutting off the B+ is NOT an option.