Quote:
Originally Posted by spacediver
btw I have some questions that I'm trying to figure out, and perhaps you could help.
Here's one of them:
According to Randy Fromm, and Kenneth Compton, the barium coating on modern cathodes provides a source of electrons, and this source is finite, and is the ultimate determinant of cathode lifespan.
However, according to some folks on DutchForce, this model of how things work is completely inaccurate: what is really happening is that the electrons are provided by the power source, and there is therefore an essentially infinite supply.
Do you have any thoughts on this matter? |
Of course, the power supply can supply all the electrons that the cathode will emit, but how many it emits is determined by the cathode chemistry and temperature. If this were not true, cathodes would never wear out. But, they do wear out.
If you look at the failure statistics of most electronic parts, you see a "bathtub" curve: a high rate of failure early ("infant mortality," which can be weeded out by a break-in period) followed by a hopefully long period of low failure rate, and then a gradually rising rate again for wear-out due to various degradations over time.
Cathodes, however, are in wear-out mode immediately when they first go into use, with a constantly rising failure rate. If the maker can maintain the correct recipe for making tubes, the rise in failure rate will be gradual enough for practical application; if not, you get some of the infamous examples of lousy short-lived tubes.
The only tube parts that are more sensitive to process variations are the photoemissive and photoconductive surfaces that were used in camera tubes.