Favorite 300B: Sophia vs KR

Maxmad, JWM,

I agree that 800 hours is a long time but, just to reiterate, in the more typical SET application, expect 400-500 hours - yes, still a long time, but the journey was not at all unpleasant. Remember, I was enthusiastic about the RPs right out of the box. For me, this was a nice surprise. Also, I’m trying to be optimistic about the long break-in and am hoping it’s a sign of extra longevity.

Maxmad, if the RPs don’t appeal to you at all, I doubt if the additional break-in will change your mind. I think that Charles1dad is probably correct when he suggests that they might not be the ideal match with your amps. But I certainly hope they improve sufficiently so that you at least feel that you got your money’s worth.

I have heard different stories that tubes can still test strong after many hours (5000 plus) but loose their life in sound. I think I have discovered this with a pair of 45 tubes that were driven "softly" by a Korneff amp. yet sounded dull (on horns) after 2 years and logging many hours. A quick check in the Hickock 600A showed a lot of life but a change to some similar tested pair brought back the life in the music. The tubes with a lot of hours still test swell today but sound soft. Not only this but some designers will tell you the same...so I think you have to trust your listening skills and have another pair to compare.
In my heart I have to believe if you get 5000-8000 hours on output tubes you might be doing good.....40,000 hours is non-sense IMO. I am glad that Phaelon mentioned this because I had no where near 150 hours on my RP tubes...maybe they are asleep yet?
My little fan idea gave me a piece of mind that it is the best I can do to extend the life by trying to cool the tubes. Once I connected the variable voltage cord and turn to ultra slow speed I cannot detect the fan running at 2 feet away but the tubes run much cooler...on the outside at least.
There are so many experiments going on in my man-cave I cannot keep up with them all.

Not sure that I understand how "tubes can still test strong after many hours (5000 plus) but loose their life in sound. .. "

From my own experience I know only 2 types of tubes that sounded freaking good, while they tested poor.

1 NOS Tung Sol 6550 Black Smooth plates

2 NOS GEC KT88

I owned quads from both at the same time and in each quad was 1 tube that tested poor, but they sounded great. How possible? Don’t know, it's all beyond me, probably the quality is so high that they still perform until they really die.

THX

Gwalt don`t know that the 40,000 hour claim by AVVT and W.E. is true or not. What are you really buying with these 'old stock' tubes that still test well? you won`t ever really know their true history of use. It`s a risk some are willing to take at ultra high prices(W.E.). I`d rather go with a new RP or Takatsuki with a warranty but of course to each their own.
Maxmad, you raise an interesting point. There are 'some' tubes that test weak yet sound good.Tubes can be a fasncinting mystery.