@mr_m , you’ve brought up an interesting subject. I like to deal with Andy of VTS not only for his high quality tubes and advice, but also to hear about his experiences in the electronics/tube world. He once told me about after WW II and Korea, the techies would grab all the tubes they could gather and ship them home. The tubes came from radio installations and anywhere electronics were used; that includes the enemy and the Allied forces supplies. Tubes were even scooped up from the battlefield.
I once ordered a rare Amperex tube from Andy, he only had one and said he would look for it on the top shelf of an area he hasn’t used for a while. I received the order and the box was dirty, faded, and tattered, just like it had been through a war. The tube inside was perfect and had incredible low noise.
There is a vast supply of those old tubes out there that never saw daylight outside the boxes they were put in.
Think of all the different scenarios where tubes may have come from.
But, I agree with
@elizabeth that there are many, many tubes being sold as NOS that were lightly used and taken from electronic devices. If they test well, they are called new old stock. It’s funny how many NOS tubes come in a generic white box.
