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This is an add-on to my previous review. The second quad of 6L6WXT+ initially biased within 1mA of each other. After about 10 hours burn-in time the bias was 4mA apart, over 10% variance. While AES did make good on the tubes they made it clear "drift" is NOT considered a defect, even on their Apex Matched tubes.

The tubes sounded ok but the variance of mA draw made the quad unsuitable for my purposes.

For me lesson learned-in the future I will only purchase tubes that are burned in then matched, which is a service AES provides on select tubes.

Very happy with AES service.

Ordered an Apex Matched quad of these for an amp I'm building. Could not get them to bias. Problem turned out one of the tubes was pulling current on the input grid. This was throwing off the balance of the bias voltages.

Contacted AES who worked with me and had a replacement quad in a couple of days. New set biased beautifully, all 4 less than 1mA difference. So far they sound great, haven't had them long enough to give a proper review on long term characteristics.

It wasn't until I saw a recent YouTube vid of one of Ed Van Halen's (RIP King) EVH 100W heads being sold that I saw the Sovtek 6L6WXT+ power tubes. The early 100W heads never came w Sovtek's, and the YT vid presenter was surprised by the tubes. I had heard of these but never got motivated. Black Friday Sale seemed like the right time. WOW. These things have THE POWER! It was immediate. I finally found a tube set that easily sounded dramatically different than anything I ever had in my '07 EVH 100 head. Smooth, edgy, gritty, precise, thick, and powerful attack is how I would describe these tubes. You will have to pull back on your amp distortion and tweak you EQ settings, but once you dial it in, "the sound" is there and available to shape. In biasing, I found a 60% + setting was more than enough to make these tubes command respect. They don't need a 70% setting. These guys are hot right out of the gate. Bias to taste, but plan on a lower setting than your used to. Use yours ears w these. Great set. Couldn't be happier. Give 'em a shot. See my pic in the gallery (look for the red MM trans and red preA tube covers)

Great tubes for my Vibro-Verb. Very articulate and clean. I love 'em!

I purchased a matched pair of these for a mesa boogie and they sounded great. Just purchased another matched pair of these for a hotrod deville, one tube had a lighter color paint than the other, the envelope was sort of slanted out of it's base but it worked fine, the other tube looked perfect but rattled and also shorted within 5 mins of playing it, looked like filament short. Tubes were biased correctly, definitely just a bad tube right out of the box as I put in a matched pair of JJs with no problems and all voltages are correct, amp in tip top shape. Will be contacting tubesandmore to see what they can do about replacing the pair.

I've tried many 6L6s and some of the Russian alternative tubes. Svetlanna, Grove Tubes, etc and I like these more then any I have tried. More lively, more punch, more dynamic. Not a overly lush or muddy, fat sounding mid to low frequency but surprisingly tight and commanding all the way to the bottom octaves. More live and realistic then any I have heard and exceptional sound stage. When I serviced my Sansui AU-111 and replaced it with a nice Yamaha the sound stage and musicality was astonishingly inferior. Not that the Yamaha was not a nice preamp it's just not in the same stratosphere. The tubes would get a 5 star rating if not for the fact that I have had to swap these out way to often in the two years I've used them. That could be due to a biasing issue with my AU-111 but that's why it's in the shop waiting for a new matched quartet of these. If you are a tubaphile that likes the old mushy airy laid back tube sound you probably will find these too analytical. To me it's the best I've heard with my complement of 12ax7s in this amp. Now I'm just hoping they last once my issue is resolved.

Did not like them. Could not bias my amp. Nothing was wrong with the amplifier.

I think it is possible for Sovtek to make decent tubes, but not sure at what level of quality control they use. The USA brands of yester-year would destroy a factory second, and they did a lot in interest of stringent quality control. On the first shipment of a matched quad from AES, one tube was just fine, two had very minor shorts, and one had multiple significant shorts and poor Emission. I returned those three tubes and got three more replacements. On the second shipment, one was just fine, two had a minor shorts. I do know know these were different than the ones I sent back the first time because the rate of emission rise was different, slower, which indicates what I call a factory second. A good tube is one that has no shorts, grid leakage, and once energized, the emission rapidly rises as soon as the filament has warmed the cathode. Aging, used tubes start having slower and slower rise of emission upon start up. Eventually, it will not rise to acceptable levels, hence low emission.

Clean loud clear, and affordable. These look like they have not changed much over some of the Soviet 5881 copies. They have bigger plates and they sound is fairly clear, clean and the highs are a little less airy than the Chinese valves. Overall, these are a decent choice, and one we use quite a bit.