Help Russian tube experts.

[twystd]

Hi, I have quite a few Soviet era tubes... 6N6Ps and 6N1P-EVs made in the Novosibirsk factory all in the 1960s. Some of the tubes have a little dab of red paint, some yellow paint, and others with no paint on the little glass point, right at the top of the tubes. I have some batches with the same manufacture date, with all three types of tips. I'm pretty sure this is some kind of grading system. Can anyone shed some light on this for me?

twystd

[m6tt]

I remember hearing something about thermal paint that changed colors after the tube was used, but I think that was red or blue.

[Colt45]

I've seen this before, I'm assuming it was just old suppliers, or perhaps the manufacturer after sitting on stock... retesting their tubes and marking them as tested.

I've had big (transmitting) Russian tubes with.. say 1965 manuf. date, and a stamp on it saying retested in the 70's. same idea I'm sure, but won't fit on a mini tube.

[twystd]

Yeah. I've heard about that, but from what I understand the thermal markings are the actual labels. I'm talking about paint that doesn't change colors, and is right at the very tip of the little glass spike, at the very top of the tube. I'll take a photo tomorrow and post.

Thanks,
twystd