I do wonder if the cathode plate coating is different on some my WE 421a's and early 5998s' they have a grainier powdered coating which has a matt finish compared to the smoother shiny black coating on some of my 5998's
Note the different types of getter and mica plate coating examples. Personally I prefer the sound of the early 5998 clear tops to the WE421a. Only the 5998 clear tops (which are early production 5998's late 1950's I believe) and the WE421a have clear tops. Regular 5998's from the 60's onwards (those commonly available) be it the single top, bottom or duel getters have silver flashing on the tops, not clear.
Warning gratuitous tube porn ahead
Some clear top 5998 and WE421a for comparison
Different textured chemical coatings on plates?
Different shapes top micas
Common 5998 with top flashing
I do prefer the GEC myself over the 421a and am still on the look out for some with MOV and MWT branding to add to a slowly growing collection.
Worth noting the GEC 6080 and the GEC 6as7g both have identical structured plates that came off of the same factory line but differing getters and getter locations while the 6080 has similar sonic traits the 6as7g version is without doubt sonically on a high plain.
Edited by JamieMcC - Yesterday at 9:54 am