Valves/Tubes was: ez80
ard at p850ug1.demon.co.uk
Wed Jul 21 14:47:00 CDT 2010
> 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.
It's getting to the point where all you can do is look in the valve data
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,
Which is not normally the most important piece of information about a
[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
Ah, so trhat's where that number comes from....
We call it an EN91 (6.3V heater, Thyratron, B7G base).
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