Dear Lynn: On Tube and Transistor Radios
Dear [Lynn],
Yes, I caught the one about the radios. I guess you really never did spend much time watching the tubes glow. Especially if you confused a tube type with a transistor type radio. 
You know, some tubes didn’t just glow orange. The tubes that served as the final amplifier stage before sending the audio signals to the speaker in many radios and record players, often glowed blue. This luminescence usually took place on the inside surface of the glass casing. Why? These tubes required a significant positive voltage be applied to their plates (anodes) to operate. This meant that electrons flowing inside between the cathode (the orange glowing part in the center of the tube) and the plate (the gray or black colored metal anode just inside the glass that surrounds the cathode) would accelerate to high speeds. Some of them traveled so fast that they’d break through the plate, and travel on and strike the inside of the glass shell, shaking up the atoms there, and causing it to radiate a deep blue color. Generally, the more voltage used, the brighter the blue light.
Blue has always been my favorite color and I think that seeing that, inside the radio, made me want to understand why it happened. Then, once I got that small taste of electronics, I just couldn’t get enough. You know that there are tubes that glow pink, orange, red, and other shades of blue? And in them, the glowing is not confined to just the glass. Some of them, such as the mercury vapor rectifier, glow a kind of silvery blue throughout their interiors. They’re somewhat brighter than the amplifier tubes in the radios mentioned above, and their glow happens for an entirely different reason. Also, still other tube varieties, such as the voltage regulating tubes, glow orange and pink (depending on the gas they’re filled with). The orange ones typically contain neon, while the pinkish ones have a mix of neon and helium. The type of gas combination used is chosen, based on the type of and extent of voltage or current regulation required. Transistors on the other hand, inspire very little visual curiosity while they operate, since the voltages they need to work, are much lower than those required for tubes. Transistors do not glow.
Ah but enough about that. You’re probably asleep by now.
Later.
Tom Hesley