VERY RARE WESTERN ELECTRIC 212D / 212-D / 212E / 212-E BIG TRIODE TUBE (211,242). Filament light up all four sections, and I. Could test at 500V on plate and got a decent amount of emission.
The limit of my testing capabilities on a tube like this. It seems that this should be good testing tube.Many people only test for good filament on these tubes, and not emission. You are taking gamble then. But at least with this one there is a very good chance tube is good. These tubes seem to be a lot.
Harder to find now then they were compared to a few years go. The item "VERY RARE WESTERN ELECTRIC 212D / 212-D / 212E / 212-E BIG TRIODE TUBE (211,242)" is in sale since Saturday, April 25, 2020. This item is in the category "Consumer Electronics\Vintage Electronics\Vintage Audio & Video\Vintage Parts & Accessories\Vintage Tubes & Tube Sockets". The seller is "jdmsales" and is located in Savage, Minnesota. This item can be shipped worldwide.