A good Internet page on Canadian Paul Dow's beautiful seminar keys.
Paul Dow started making keys in the basement of his Winnipeg Canada around 1943. He made speed keys up until around 1957 when the business was moved to Minnesota. After this the company name was changed to Dow-Key Microwave, specializing in switches and relays.
Many amateur radio operators who had separate receivers and transmitters used Dow Key coaxial relays with auxiliary contacts to switch the receiver into standby during transmission.
73
DR