I always use the "Steam Console Client" (
https://developer.valvesoftware.com/wiki/SteamCMD). It does not require a steam account and is quick and easy.
login anonymous
force_install_dir /home/sd
app_update 294420 -beta latest_experimental
Adjust the install dir if using Windows to something like c:\sd or wheverer you want to put the server files. I'm not sure if 17.4 is the default or not at this time, but including "-beta latest_experimental" on the app_update line will get it for you. You can also try "-beta a17.4"
app_update 294420 -beta a17.4
Please note that if you use an invalid beta, it will not complain or tell you so, it will just download the default version, which may not be what you want. So after you get it downloaded, make sure it really is the version you wanted. I think the only way to find out the version is to run the server and then either telnet into it, or look at the server log. You will find a line like this:
2019-06-08T09:28:24 0.123 INF Version: Alpha 17.4 (b4) Compatibility Version: Alpha 17.4, Build: Linux 64 Bit
(or it will say Windows 64 bit if you are running under windows)