Specified current AC/DC - This option includes families of tubes, whose cathode/heater assembly was purposely designed to be connected in series with heaters of other tubes, in order to operate directly from AC/DC mains. It includes several families for which the most popular current values where 100 mA, 150mA, 200mA, 300mA, 450mA and 600mA. For example PCC85 or 6AU6A. It also includes some rectifiers, as PY82 or UY82.