babysitting the burning-in process of new tubes, especially tubes you are trying for the first time, is an arduous and nightmarish process. it requires tons of patience and good faith. at many points in the first 70 hours, the sound was so bad that i couldn't bear to listen to it. if you are paranoid (like me), you may even think that your amp has got problems!
therefore, it makes sense for a lot of tube dealers (in USA especially) to pre-burn-in the tubes for 70 hours before they sell them to the public to avoid all these growing pains.
here's a blow-by-blow account of the first 70 hours...
first 5 hours - sounded promising. strong presence. highs are slightly strident. bass is muffled. everything is a bit taut and tense. but overall a good preamble to what is to come. 75% on my score card.
5-20 hours - horrible. shitty sounding. no energy. soft. sissy. closed-in. no definition. blur. totally unlistenable. extremly low gain. these are the worst stage of the tubes.
20-30 hours - highs started to come out but the overall presentation is still soft and recessed. still no definition. very soft gain (volume) . very very unbearable.
30-40 hours - somewhat improved. highs become better. definition becomes better. still inconsistent gain - sometimes loud, sometimes soft. mids and bass are still not well defined.
40-50 hours - getting much better. still lacking of energy and gain. 75% on my score card.
50-70 hours - bass still hasn't come out. anaemic presentation due to lack of bass. highs are 80% defined. still low gain. separation is no good. lacking oomph.
70-80 hours - voila! bass came out though still puffy but strong and tuneful bass! the sound gains energy! 85% on my score card. highs are still not the best yet. but overall quite satisfying.
80-90 hours - highs started to develop. mids also gain definition. 95% on my score card. this tube really needs more than 100 hours to sound its best!
characteristics of re-issue tungsol 6550
the tungsol sound is characterised by two things - robustness and the voluptuous bass. the mids, after 90 hours, still lack a wee bit of resolution and details. the bass is fat, taut, clean and tuneful, in fact, the bass is the best thing about this tube. the highs on the other hand, is not the most refined/pristine, compared to NOS 6550s. but we are hopeful that all these will further improve after 100 hours.
overall, it should partner well with systems which are not too "fat" or "tubey". considering that it is a current production tube and it is only 90 hours burned-in, it has far exceeded my expecations. i would give it a provisional score of 95%.
i would further update this after 100 hours.
晴空万里的"天空" [the sky is the limit]
4 days ago