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It seems supply of NOS, originally boxed 6SN7, has almost completely dried up at the moment. It is weird, we would have to buy 6SN7 now, for a higher price than we sold it, just some years ago. What is still for sale, is single pairs by private Ebay sellers. Said always to be never used before. I wonder where they all went to, those tubes with some years of occaisional use, and the old boxes carefully saved. What tube dealers are looking for, is always many pieces of the same. That is much safer, but it is exactly this type of NOS, which is totally and completele gone since 25 years.

Chinese NOS, with metal base, it was the cheap junk of the 1990's. This is heavily sought now. Russian 6H8, I could buy those for 30 Euro in boxes of 100. So not per tube, but 30 Euro for the box. That was long ago. But at that time, there was little use buying it. Besides, nobody was buying those "bad sounding" tubes, as they could still get RCA and whatever preferred brands. But now look what happens today! People are t buying them, specifically asking for REFLEKTOR brand, or metal base Chinese NOS, because they say, there is nothing like it. Very weird. If you understand this, you understand more than I do, but one thing I can say for sure: Prices for really good 6SN7 NOS are rocketing, and all the usual stories about NOS apply here. Including the fact that everybody is surprized about the effect.

Here is something important with 6SN7 NOS, I know this is so, but I can not really prove it. I expect some of the gas, bound in the Barium Getter, over many decades gets released, and one way or another, finds it's way the cathode. Don't call this impossible, because in the getter is realy quite a lot of gas bound, and already the tiniest bits can damage the cathode. It is a fact, the longer such a cathode was stored, the more unlikely it recovers fully.

In any case, when testing NOS 6SN7, they all have in common, that plate current is just a tiny fraction too low. Not much, but it is. It will improve by burning in, but not be fully cured.I think this is a thing we just need to accept. This is NOT a problem, but it is a small issuse.

An EXCEPTION to this quality issue are the so called CHROME TOPs.This is a wrong word, for older type Aluminum getters. They look like Chrome indeed. Also they are not always chrome TOPs, but also Chrome SIDES exist, as found with many VT231 from WW2 production. These are simply the BEST. Gettering technology was much different from modern Barium getters. These tubes were vacuum pumped, but a tiny bit of gas was left intentionally. This gas made it possible to out glow the complete tube, with mild RF energy, just enough to create a plasma in the tube. A Plasma is nothing but a lighting gas, same as in neon lamps, or Geissler tubes. Then, when out glowing was completed, the RF energy was increased, and at that point the Aluminum getter would begin to melt, and flash against the glass. Automatically, when the getter flashed, the high vacuum was created, the plasma stopped lighting, and the process switched itself off. This would create a perfect, high vacuum. Unlike Barium getters, this vacuum does not seem to degrade during almost 80 years of storage. This technology was obsoleted however around 1945, and replaced by the more comfortable Barium getters. So any Chrome Getter tube is that old indeed, and most likely still fine condition.