I was browsing the RF Parts site, and surprised to discover that the only "3-500" tubes they currently offer are the 3-400Z Eimac NOS ($329) and the 8163 Amperex NOS ($329). What happened to the currently-manufactured Chinese 3-500ZG? There is no direct link to it, but Google turns up the following link: https://www.rfparts.com/tubes/tubes-3500/3-500zg-prc.html ...which says "$169 - Out of Stock". No information on why or when it might be back in stock. Thetubestore.com lists the 3-500ZG as "Out of stock ($199)." The DXEngineering site does list "Ameritron 3-500Z Replacement Power Tubes 380-0500GT, Replacement For Power Amplifier, 3-500ZG, Graphite." ($239). Estimated ship date 10/23/2018. Anybody know what's going on here?