Note about storage of AVVT tubes: It seems the storage time of those tubes is minimum 10years, and after that period, all they need is a short warm-up and you can store them for another period. (we write this in the year 2009). It seems at this moment you need to pay no special attention to all AVVT branded tubes. Just plug them in, and that's it.

The VAIC-VALVE tubes that are 10...15 old now, may be going to need a (professional) burn-in before first use. (Such a burn-in you can not do yourself). After this burn-in they are ready for another storage period.

Does that mean older tubes are bad? No! But... you need to take care of the following:

If the tubes were stored longer, like 10 years or more, they might need to woken up in a controlled way. This is normal, and you should not be dissapointed if such tubes do not test very stong, right out of the (NOS) box. If they test at 70% or more DC current (the most important test for any tube) you can use the following procedure, to re-activate them.

If lower than 70% they most probably can be brought back to life by an epxerienced person, provided the tubes are really NOS, and you have not been fooled with used tubes put back in the original boxes.

If a NOS tube is initially (at a very short test) at or above 70% DC current, here is the way to go:

THIS PROCEDURE IS DONE ON ALL AVVT TUBES WE SELL

1. Run the tube with filament heaters only, for 30 minutes.
2. Set up the tube for maximum power conditions, and then check if the tube draws 100% of the plate current it is supposed to draw at those conditions.
3. If below 70%, stop here. (see note at the end of the text)
4. If above 70%, observe if plate current tends to go up or down. If it tends to go below 70%, stop here. (see note at the end of the text)
5. If it goes up, let it run for 30 minutes, and observe if the plate current will not go above 100%. If that happens, stop here. (see note at the end of the text)
6. After 30 minutes, reduce the grid voltage such that you have 50% of maximum plate power.
7. Run the tube for two hours in this condition.
8. Now test it for transconductance, and DC current. When around 85% the tube is ok, and can now be put into an amplifier. Re-Test the tube after 50...100 hours, and it must be at 100% plate current.
9. When the tube is at 100% right away, it needs no further treatement. (so the end user can do the burn-in of 50...100 hours in the amplifier himself)

All AVVT NOS tubes I had so far, passed he above procedure perfectly. Most VAIC-VALVE also, but some needed a more professional wake-up procedure, and then were very strong again.

The above process is a very good idea for any NOS tube that has been sleeping very long. Then they can be safely stored again for another period. In case a tube was stored longer than 10 years, you may find the transconductance is 30% reduced or more. So you must verify the original old DC test data, if available. If DC test data got lost or never existed, you have to work with transconductance data, but that is not as good as working with DC current data. In case you observe lower DC current, you will also have lower transconductance, but how much lower nobody can tell.

Remember, this is only the case when the tubes were stored from the beginning, and never used ever since. This is nothing unuseual, and it is almost normal with NOS tubes, like 6SN7. I bought a NOS pair WE-205D, that was only testing "fair". After re-activation, it was exactly like on the datasheet again. When the tubes are used every now and then, they will just stay in good condition. So here comes my old saying again, that good "used" tubes can be better condition than random NOS tubes that were stored ever since. I also had NOS 227 tubes from RCA that could not be brought back to above 60%. These had been sleeping for 80 years, and they would have been fine of somebody just switched them on three or four times during that 80 years. However, it was not done, and they were lost. The first time I opened the boxes, the boxes fell apart in small pieces, so the tubes were really never taken out. The tubes came out looking nice, but test values were very weak.

IF THE PROCEDURE WILL NOT WORK. There are no general rules what to do now. It requires experience with the particular tube type, and understanding of the processes inside the tube, and these are many, and not the easiest to understand. If you have a "transconductance only" type of tester, you can not say very much about the tube condition, unless transconductance is very strong. When this has happenes, do not use the tube, or your attemps may make things worce, or damage the tube permanently. Such a tube can be brought back into good condition, when you have the equipment for it. You can send it, and we can do that for you. So far, this seemed only necesairy with the Vaic-Valve 52B's from around 1996, but it will probably also be necesairy with other tubes when the years pass by, and older NOS tubes are found.

CONCLUSION : May seem too simple, but it is really so. Buy only the NOS tubes that we have on stock, we sell you very good materials. When out of stock, use the equivalent EML tubes otherwise.