At this website we show since 1998
ALEŠA VAIC VACUUM TECHNOLOGY
(Now NOS tubes)
FAILURE STATISTICS OF AVVT TUBES
I added this text in 2016, after letting this website intentional unchanged since 2001, so far.
However it is necessary now, since some crooks have been selling historical factory rejects as NOS tubes, beginning 2016, and one way or another, these tubes landed on EBAY, or other flea markets.
I see them go sometimes for 1600...1800 US$ a pair, and it hurts to see these are series numbers, I have send officially back for destruction, in the years 2000...2001.
Unfortunately, I learned now (in 2016) these tubes were not destroyed at all. Apparently they were collected, by whoever that was, but this is all I can say for sure. Otherwise they would not pop up now on Ebay.
For the rest, who is selling them, I know nothing about it. Believe me, I find this situation extremely disturbing. Sometimes, Ebay bidders know me, or know to find this website, and ask me if the AVVT Series numbers are ok. This is a bit boring for me of course, to tell many people if the series numbers are good or bad, since I am not related to AVVT problems any more ever since 2001.
However, now with this new situation, I decided to place the failure statistics online. So you can judge it for yourself.
Please note, at that time, not all series numbers were captured by me. So a reverse conclusion is not always correct. Still most REJECTED numbers are in this list indeed.
Still, this list gives a good impression of what where good periods, and what not. So if the series number is for instance like 25xx, you will recognize, there were many bad ones in that series. Adjacent is the 26xx series, and that was a much better series. Not perfect but a lot better. So a 25xx tube is worth much less than a 26xx tube, so important is, if the adjacent numbers are good, or bad.
Also you can see from this list, AVVT quality problems were completely solved with series numbers higher than 6100. From there, the defect rate is almost zero. I would say any series number above 6100 are amongst the best tubes you can buy. Feel confident to pay any NOS collectors price you think is normal. As you will see, that's unfortunately not what they are selling on Ebay. Note, 32B is good at series number above 5300 already.
So to say it again, some crook is now bringing the old factory rejects on the market, and the bad guy may not even be the final seller. Though of course the seller can help us to shed some light on it, as he knows at least where he got them from. Please let me know, if you find out names or sources. The internet has a memory, and it is a powerful memory.
These tubes series numbers are marked in my list as: "Returned for destruction". The problem with those tubes is, they are initially strong, but they will last a couple of hundred hours only, instead of 5000+ hours which you can expect from a good AVVT series number. You can definitely not go by test values that you get from a tube tester. So they will test good, but latest after burn in, problems will begin, such as hum, low output, distortion, and other signs of emission loss. So the problem is not vacuum loss, but emission loss. Actually I see these are sold including certificates, with signature and stamps, but this is only a sheet of paper. At least it is not possible to change the series numbers inside the glass bulb.
This list is an extract. For myself, I have more complete version, with tube test data, initial buyer, shipment country, etc.