Re: Another (possibly silly) valve question
My research indicates that cathode poisoning is caused by the cathode coming into contact with traces of unwanted chemicals, e.g. oxygen, aluminium or various silicon compounds. Typically, these enter the valve envelope via leaks in the valve envelope, by over-running the valve (so that the various electrodes become stressed and emit impurities) or by deficiencies during valve manufacture. The result of any of these effects is decreased emmissivity from the cathode surface - known as 'cathode poisoning'.
Therefore, it seems that the question really boils down to this:
does powering valve filaments - without cathode current flowing - cause these impurites to become activated and thus attack the cathode?
For low-power valves, I suspect not - but I cannot find any authoritative statement anywhere to confirm or contadict this.
Al / Skywave.
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