"Simple," said Barney in a cheerful tone. "Thank God for their habit of drawing pictures. Here we have the well-known H tube. The electrodes are signified by the symbols for the elements used. The Periodic Chart in the first section came in handy here. But look, master mind, this dinky should be evacuated, don't you think?"
"If it's electronic or subelectronic, it should be. We can solder up this breach here and apply the hyvac pump. Rig us up a power supply whilst I repair the blowout."
"Where's the BFO?"
"What do you want with that?" asked Jim.
"The second anode takes about two hundred volts worth of eighty-four cycles," explained Barney. "Has a sign that seems to signify 'In Phase,' but I'll be darned if I know with what. Y'know, Jim, this dingbat looks an awful lot like one of the drivers we use in our spaceships and driver-wing fliers."
"Yeah," drawled Jim. "About the same recognition as the difference between Edison's first electric light and a twelve-element, electron multiplier, power output tube. Similarity: They both have cathodes."
"Edison didn't have a cathode—"
"Sure he did. Just because he didn't hang a plate inside of the bottle doesn't stop the filament from being a cathode."
Barney snorted. "A monode, hey?"
"Precisely. After which come diodes, triodes, tetrodes, pentodes, hexodes, heptodes—"