A few years back I built an ANK Kit-1 300b stereo power amp.
The rectifier tube arked upon power up. I contacted ANK’s builder at the time and he suggest trying a new EH 5u4gb. Told me to buy two or three cause one might ark even new, so throw it away (and any other rectifier tube that arks at startup).
I bought three and only one arked at startup. I marked it and some others but never threw them away lol.
It’s been working fine ever since although I don’t use it constantly.
I did notice shortly after that ANK started including the EH 5u4gb with their kits. But that was then.