I was reading the description of this Alpha 6-meter amp that claims "Robust 4CX1600B (Svetlana GU-91B) which is very affordable and readily available." ** Has the 4CX1600B gone back into production? It's listed as a GU-91B from the company that took over Svetlana but I've not found any source for them. 73 Roger (K8RI)