I have some of that as well, but I have to say I'm getting very good service from the last 3 AM tube rigs I have ... a couple of 5kW Power Rocks and a Continental 316F-1. The Continental is about to give way to a DX-10, but will make an excellent aux.
So long as the tubes are available and Continental continues to support the rigs, I don't see the owners replacing the Power Rocks any time soon... which is fine by me. They are very good-sounding transmitters and aren't giving me much trouble at all.
AM Radio discussion. Directional arrays are FUN!