Labeled and boxed as National 5AR4. The most durable, overdesigned, 5Y3 you'll ever see. These have indirectly heated cathodes which means that they turn on (very) slowly like GZ-34/5-AR4s. This feature helps to extend the life of the other tubes in your amp.
Mike,
I wanted to thank you.
This tube sounds great in my Victoria 518. It really is built like a tank and really brings out the sound of the amplifier.
Thanks again.
Christian