Radio tubes

[pushkins]

Hey hayzee, I have a question, in old radios they had tubes why did these tubes have to "warm up" before you could hear the radio ?

[HayZee518]

radio tubes

the early radio used vacuum tubes. inside is a coated filament that needed to heat up to incandescents (spelling?) before it would freely emit electrons. the electrons were attracted to a metal "plate" that operated at a minimum of 180+ volts. in between the filament and plate was a control grid, much like a screen with holes. this also operated at a given voltage to control those electrons going to the plate. how much or how little electrons made it to the plate resulted in high, medium or low amplification. the filament emitted electrons. this is called direct excitation. the filament is called the cathode. there was another smaller plate that was heated by the filament that was also called the cathode but it is known as an indirectly heated cathode.

[pushkins]

so....in dumb dumb terms, that means that as the tubes warmed up they allowed the passing of current ?

[HayZee518]

tubes

yeah, in laymans terms. if it didn't warm up and glow, it didn't work. the filament you sometimes refer to as the "heater" which is what is does, it heats up to excite the electrons in that white coating on the filament or the indirectly heated cathode. transistors on the other hand do somewhat the same thing, but the inside construction is different. there is nothing to heat up, but the theory is the same. a transistor type P-N-P or an N-P-N has three elements. One - the emitter [same as the cathode] base - [control medium] collector - [plate] the transistor is made up of precious metals, "doped or deposited on a substrate. this substrate may be fiberglass or regular glass or even plastic. it may consist of arsenic, gallium, gold, selenium, usually any of the active metals on a periodic chart of the elements.
N type materials are negative. P type materials are positive. the emitter always gives up electrons, the collector collects the electrons, the base controls the amount of electrons transferred. tubes operate on DC just like transistors, but not at that high of a voltage. the junction where the emitter and base meet is called the "doped region" - the theory behind the transistor is the transfer of electrons to "holes" which accept electrons and blocking out others.