These are a small selection of used HF pentodes using the Ct9 side contact base. They carry the BAL716 stamp showing that it was made to the German Luftwaffe and Wehrmacht specification had such a proof mark. RLM stands for Reich Luftfahrt Ministerium and was used from 1933 to 1945. These valves are thought to date from 1939/40. code 12 39 is probably the date code.