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I have a quad of these tubes cooking in my primaluna prologue 2 right now. I like the balance and warmth of the tube very much. I have about 20 hrs on them. I am hoping for the top end to open up alittle more and for a little more detail in the mids will this happen with more time????
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it's broken in. After that it really opens up. When my tubes were new, I had to crank up the volume. It took about 72 hous for the tube to break in. Now, I like them better than other current production 6550/KT-88's.
Mine are still breaking in. Not sure how much time. Less than 100 hours. My tubes never sounded weak. They just sort of gave me a headache when I listened to them to much or too loud. But they had potential. Cymbals had a pie plate sound sometimes. But as the tubes break in the are sounding better and better. Starting to sound very musical. They are a bit rolled off in the treble with a pretty warm midrange. Not quite as warm as SED just a little different. Hopefully they get even better but they are pretty nice right now. Are they the best new stock tube? Don't know yet. NOS Tung Sols are definetly still the best.
Six weeks ago, I ordered a quad (not matched) of these with the solid plates for my "triode" connected Citation II.
Before ordering, I spent at least thirty minutes on the phone with Peter Russell, their Chief Technical Engineer; he's a very knowledgeable person and definitely a "tube head". He told me a great deal about their production facilities in China, the clean rooms and quality control methods. The factory makes tubes for several vendors and not just the 6550's. These are modeled after the GEC and he thinks they sound even better than the original. Now, since I don't own any original GEC, I can't make a direct comparison, but I can compare with NOS Tung-Sols and my Jim McShane Type I Ei KT-90's. He (Peter) also says running in UL mode at 425V on the plates… in AB1 their good for 50W each…hmmmm…I do wonder about that one!Construction…these tubes seem to be well made, uniform bottles which are solidly attached to the base. Interior elements, plates and micas are straight and uniform among the quad. Pins are solid and straight; the getter flashing is good and is remarkably uniform in my quad. Another thing I noticed is these tubes have a real “heft” to them.
Electrically…with the individual bias pots on the Cit II set at minimum, current on all tubes was within .335MA of each other after a one hour warm up…this really surprised me for non-matched tubes, I later set the bias for 85MA and it’s remained stable since. There are no red plates or other anomalies that I’ve noticed.
Sound… I’ve found these tubes do need a long break in—mine didn’t come into their own until after 100 hours or more; they’ve settled in now though and are still improving; the tubes are dead silent. Are they a Tung-Sol, well no, but they’re sounding pretty darn good; I think a very choice for every day use. So far, the biggest difference is in the midrange, not as silky smooth/mellow as my TS’s, but a good tight and plentiful bass exists; it has a clean crisp top end with plenty of detail, sound-staging is good, with excellent dynamic detail across the audio spectrum and a wide soundstage to boot. Also, at this bias they seem to have a bit more headroom than the Ei KT-90’s or the TS’s; all-in-all, a very listenable tube in my setup.
For a $20 tube I think its going to be hard to beat in my current system. So, if you’re looking for a modern day KT88 that's a very, very good all-rounder, this could be the one.
As for reliability…we’ll see. (an addition here) The reliability has been excellent. I have ordered, and am using, four quads from Penta with no a failures; I believe the long term relibilty will be very good.
Regards,
"Kico"
"Also, at this bias they seem to have a bit more headroom than the Ei KT-90’s or the TS’s;"
'Headroom" at least to me, is what I describe as how loud a clean channel will go before 'breaking up' into distortion. I know this is often associated with the amp's wattage, but I also know it's a bit misleading and rarely too accurate. Yet, a 100 watt amp should have more headroom than a 10 watt. I also know are many other factors that contribute to the perceived headroom, not in the least--
The amount of gain stages in the preamp
How hot the preamp and power tubes are biased
The efficiency of the speakers and output transformers
Whether the rectifier is tube or solid state and probably many more.I noticed the volume before signal breakup was higher on the KT-88SC's than my Tung-Sols and the KT-90. TS's went first, then the KT-90's, and finally the KT-88SC's. All were biased using the same line voltage (117V) off my auto transformer and were at 85ma.
Again, just my experience...
Regards,
"Kico"
Thanks Kim.There is one variable that can affect the "breakup" point, and that is the bias voltage. While the bias current was the same, the bias voltage it took to achieve that remains a variable.
For example, if it only took -40 for tube "A" to be biased at 85 ma. then a positive going signal larger than 40 volts will drive the tube into grid current. A tube "B" that biased at -45 would have more "headroom" before that would occur. A tube "C" biased at -50 would have the most room before it went into passing grid current - but it would also be closer to cutoff if the negative swing was large. A 50 volt negative signal added to the -50 bias puts the grid at -100.
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Regards,
"Kico"
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