THE GREAT MULLARD MAGIC BLOG — valve end of life

If a valve passes an anode current of 1mA then this equates to 650, 000, 000, 000, 000 electrons a second.  When you consider that an output tetrode like a KT66 can pass up to 100mA in anode current then as Cilla Black would have said 'that's a lorra, lorra electrons!'    I think this little fact demonstrates quite well that over a period of anywhere between 2000 and 8000 hours on average, a valve may loose a proportion of it's emissive properties.  During the early life of a valve, the effect of emission loss is realtively imperceptible but after...