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Can someone tell me why the smallest of tubes do not have a base, ie, 12AU7, 12AAX7, EZ81, 6DJ8. Thanks.
[Badfinger]
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The V/T industry grew out of the lamp industry and used many of the same techniques in manufacture, so the first V/Ts were globes with a "pinch" through which the leadouts were taken. This required the addition of an external base which interfaced with the socket in which the V/Ts were inserted.This is an expensive and cumbersome way of building V/Ts so as the industry became established it sought cheaper methods of manufacture. One of these was to use what was called a "button" base, a glass disc with integral pins to which the electrode structure was attached. This was then welded to the tubing which created the envelope and extraction and pinchoff were performed through the top of the assembly, creating the small glass nipple.
All of this was independent of miniaturisation, which didn't have much effect on the economies of V/T manufacture. Less materials were used but smaller structures are harder to work with and the physics of cathode emission create a trade off between cathode size and life for a given emission level.
Hi,Another reason was - as stated with the introduction of sylvanias lock-in - that shorter leads gives lesser capacitances and so detter data from the tube.
There are tubes that can be found with different bases, and those with the smaller structure, lesser "base" usually have better data.But I think there was an economy of scale as well :-)
For power tube, between the flexible wire and thicker pins at the tube base, since I did stripping up a metal base EL34(what a shame) for re-soldering. In fact, it could be re-soldered at the pin without such "operation",my mistake.
BF,Think that the idea was to reduce the overall size of tubes.
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