I4053 / J4053

I4053 tetrode used as a mixer tube. Starting in 1929, indirect-heated tubes were manufactured in France, initially using a (drawn) tungsten filament surrounded by a small nickel tube coated with oxide, which resulted in a long warm-up time, then came the small silica tube (which corrodes the tungsten), which did not prove reliable, followed by clay insulators and, with this family of tubes, a special coating process.