Old tubes such as the stellar RCA 811A are about extinct. The Chinese 811A do not last long and some report the output falls off after 2 years use. Some fail new out of the box. The old RCA would last 20 years or longer, so what is a solution to low 811A tube life? The Russian 811 called a G-811 is a superior 811A that will also last 20+ years like the RCA 811A. The difference is likely the RCA 811 having a thoriated filament. Thoria is a natural occurring radio active material that maintains the electron cloud in a tube tungsten filament under a vacuum. The process also requires carbonization of the filament to control thoria loss. The process takes more time to build a tube and thoria is not exactly easy to source and use. Thoria is a non-regulated radio active element. The Chinese are cheap and will produce a inferior tube. In other words, toss you under the bus for a dollar. The Russian G-811 is properly manufactured like the old RCA 811A. The G-811 are sold on ebay for about $17 each or less cost vs the Chinese 811A.