the infamous 6GH8

[drh4683]

I am working on a ctc22 set that uses 5GH8 tubes (series string) and ALL the tubes were defective, either shorted or low emission. The same applies to the 6GH8 used on all the other RCA chassis, and most magnavox chassis. Anyone know why these tubes frequently fail? The few nos 6GH8s I have are almost totally gone because all I do is replace them and thats like 8 per set.