Radio symbols named

These are early US symbols, other countries may have designed their own. The first 3 valves are battery designed with direct heat to the Cathode and use less current than mains valves, they were improved over the years. The Screen Grid valve was later called Tetrode. These symbols were draw-up in the early days of radio or telegraphy and many are still in use today. Condensers were later called Capacitors.

Some later improvements the the vacuum valve/tube shown here in UK style