ez80

Most of the US tube numbering systems are today fairly meaningless, and yes, the best way to know what tubes you are looking at is to pretty much know what circuits you are looking at. The initial "standard" (an example would be UV-201) set by RCA was quickly corrupted by the independents, so the industry set up a new standard that we all (US) know and love. I suspect that the choice to standardize the filament voltage and active number of elements in the type number, yet leave out the basic function, was driven by the idea that many radio designs could easily morph, simply with a tube swap, in order to meet a new demand. An example might be changing a standard AC power radio into a farm set into a car radio - mostly with only a tube swap involving filament changes. In an early 1930s context, this starts to make sense. However, with the explosion of new types, I think this was all corrupted as well, and by the late 1930s it was pretty much as meaningless as it is today. The industry standard 55xx series, where most computer tubes reside, chucked all ideas of encoding stuff in the number, and in a way has remained very intact. The European system used this same idea, tried to encode a little more into the type numbers, but still managed to corrupt itself. An article in Tube Collector magazine outlined the system, and there are an astonishing amount of inconsistencies. In a way, it tried to be too clever. Of all these systems, the most simple ones tend to be the best - do not encode anything into the type numbers. If a tube user needs to figure out just what a specific tube type does, he probably has no business sticking his nose into the radio in the first place. The award for most retarded tube numbering must go to the British. Apart from the military's CV (common valve) system, which almost nobody but the military uses, the British system was a mess, with numbers and formats specific to the government agency or industry that wrote the databooks. Often these numbers would even foul each other. The best example is the VT90. If you ordered a VT90 each from the Army, Air Ministry, and Post Office, you would get three completely incompatible tubes. And during World War 2, if you ordered a VT90 in Britain, you might get a humble little US made 6H6 dual diode - a "fourth" VT90. -- Will