Valves/Tubes was: ez80

[Tony Duell]

> That's true, but only in those cases where the shell (or any other 
> element) is brought out to a base pin.    The 1934 standard says that 
> an element has to be "useful" and have a connection to be counted.  

Right,..

It's getting to the point where all you can do is look in the valve data 
books....

I still much prefer the Philips coding scheme. it tells you a lot of 
useful information, and exceptions are not common (put it this way, I've 
never seen a valve which doesn't fit the scheme correctly). 


> 
> So, a 6L6 has heater, cathode, control grid, screen grid, plate and 
> shell all connected to base pins.  The beam-forming electrodes aren't 
> counted, so, for instance, the 6F5 triode has exactly one fewer 
> "useful" electrode, even though it has two fewer elements.

It appears that sometimes you count the tap on a heater (e.g. 35Z3 
against 35Z4), sometimes you don't (12AX7 has 2 cathodes, 2 grids, 2 
anodes and a tapped heater). 

> 
> The other requirement is that the tube must have been introduced 
> initially in the metal shell form (I can't think of any that were 
> glass, then metal, but there may be some.)

My guess would be tuning indciators (magic eyes, or whatever you call 
them). A glss window is essential for that type of device, and I would 
assume many exist only in glass envelopes.

> 
> An "S" as the first part of a middle two-letter pair signifies a 
> single-ended tube, which was not universally followed.  Rectifiers 

There are many single-neded valves (no top cap) without the 'S'. 

> *usually* have a high-middle letter (e.g. 5U4, 5Z3), but sadly, there 
> are many exceptions.
> 
> The most reliable part of the number is the suffix.  e.g. G = glass, 
> GT = short glass, GA = improved glass version, GY = micanol base, 
> etc.

Which is not normally the most important piece of information about a 
valve :-). 

[I thought 'GT' was 'Glass, Tubular', meaning a straight-sided envelope]

> 
> In 1942, the RMA introduced a scheme for special-purpose and 
> transmitting tubes, that was called the "1A21" system.  The first 
> number represents the power rating, the second, the tube type (e.g. 
> diode, triode, etc.), the second and third numbers are assigned in 
> the order of introduction, starting with 21.  So the gas thyratron 
> 2D21 tells us nothing more than it's a tetrode rated for 10 watts or 
> less.

Ah, so trhat's where that number comes from....

We call it an EN91 (6.3V heater, Thyratron, B7G base).

-tony