Reliability issue - Nagra VPA power not KR tube

in term of 845 tubes, I've tried 3 different pair in my system (Mastersound Reference 845/Italian). I tried the new 845M and was totally disapointed by the sound. Then I switched to Fullmusic 845 ($820 for quad) and got disapointed as well.
My current setup is using Valve Art, which I'm very satisfy with the sound. However, these Valve Art are getting to old so time for replacement. I just recently ordered 4 845tube from KR, let's see what's the result!

Jjwa. The difference with the 845m is lower noise floor, you can hear into the music much easier picking out what is in the background, they are faster, more dynamic with better defined bass, the top end has much more air making cymbals more real also there is less grain making them more listenable and more enjoyable. In a word more Natural.You only have to turn the bias pots very little and your in the green.You will be impressed! also iam using au24 cables with superb results.

With respect to the original question, Nagra has been making bulletproof gear for a long time and I don't think the VPA is any exception...unless you mess with them.

I found the KR 845's to sound exceptional. Subjectively more powerful, with a darker tone and a richly saturated, more vivid sound. Very nice in my system anyways. Only problem is that one of the tubes "took out" one of my amps after some 20 hours. Said tube was said to test fine afterwards and last I heard Nagra was said to be working on a fix for this recognized problem with no resolution as yet.

I'm currently burning in the new 845M's and while they sound fine, the KR's sounded better. If I were a VPA owner, however, I'd probably stick to RCA spec'ed 845's rather than the KR's which are not as, for example, they use a different filament that draws more current. Therein may lie the problem. The VPA could probably be modified to use safely with the KR's.

One word about the new 845M's...one of my quad was misshapen such that I could not fit the tight VPA tube cage over it. This was replaced only after some hassle so when ordering make a point to mention your amp and these cages.

How does the Super TNT 845M sound compare to the Golden Dragon Select? How would people rank the sound of 845 choices and their most promoment characteristics? Ten being the best.

I have had a pair of VPA's for about 3 years and a year ago 1 tube went bad and I replaced with tubes from Sophia Electric. They have tubes from Shuguang in China and a matched pair for $210 is great. I installed the tubes and had to adjust the bias somewhat and realized then that they were better and run cooler than the orginals. I would do it again. My VPA's were made before the KR tube came out.