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In Reply to: EI 6CA7 Fat Bottle burn-in time posted by dubai2000 on September 19, 2004 at 03:48:26:
Yor description of your prefered sound perhaps indicates a lack of midrange accuracy. The only burn in effect of a longer storaged tube is a better vacuum after some hours of use with high plate tensions and moderate plate dissipation( perhaps the half of the ratad max dissipation). This is with a well done cathode.
The aft bottle is a beam power tube. And therefore it has lower third harmonics content. This would produce a more forward soundstage with a little bit brighter midrange. I think there wouldn't be further changes in the next future. Perhaps it would be helpful for you to visit a classical concert and compare your different tubes after this performance in the evening. I am sure that this would generate new aspects of your amp.
Follow Ups:
My Marantz 8B sounded brittle and 2 dimensional with 6CA7 Fatbottles even tho' I was very patient with these and gave them a few weeks to burn in
The Valve Arts lacked punch by comparison and sounded rounded but slightly vague
I am now using one 6CA7 Fatbottle and one Valve Art EL-34 a side as these can be individually biased; this combination seems to get the very best out of both tubes and is the best my 8B has ever sounded
Mullard/Philips E90F mesh plates as 6BH6 substitutes sound better than the very best of USA NOS; and Tung Sol black plates or RCA Clear tops in the 6CG7 sockets is the best I have found so far for this Amp
As you have both tubes, try this, I think you might be pleasantly surprised
Now here is an idea!
I have repeated the power tube 'mixture' and so far I like what I am hearing - thanks a lot for the suggestion.
E90F I already had in the amp; as 6CG7 I also like some Matsushitas (sp?), actually seem to prefer them to the RCA Clear tops.
The Matushita 6CG7 is the best NOS one I have. The measurements of the new EH 6CG7 indicate that this tube could be better. Worth a try!
I have been contemplating trying the EH 6CA7 as well.....and I might actually do so, but as it is this VA EL34/Ei 6CA7 mix sounds quite good.
Grins
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