Just a little curious.
Do any of you know the reason that 50L6's and their equivalents like 35L6 and 25L6 are grey-painted inside?

I have a clear glass one here that was working quite well in a plastic radio where the case was getting rather warm... However, when I replaced it with the grey-painted variety there seems to be a significant reduction in the effective heat on the cabinet. Though the tube still roasts my fingers like a frankfurter as it always did ...just the same way ...if I don't wait long enough before pulling it. ( ahh ... how I love the smell of burning flesh first thing in the morning)

Now...I could be wrong (could be just that old electronic-placebo psycological effect) but it sure seems somewhat cooler now.

Anyway, I'm assuming that this temperature thing is just a 2ndary benefit and the the inner coating is supposed to benefit another purpose. Any clues?

thanks..

I don’t know, but I hope someone here does.
I have bought several 2A3s with the black out coating. They are always more affordable, it seems the audiophiles think they don’t sound as good in high dollar SE amps so they don’t snap them up at $80+

Black coating is for better heat dissipation and for electrostatic shielding. Coating is graphite, similar to the aquadag coating on picture tubes.

T.

many many years ago i look a grey tube in a old computer sistem.