UPDATE
Ordered my matched quad of Sovtek 5881WGC's from The Tube Depot (http://www.tubedepot.com) online. Let me first say these guys were top notch. I paid via Paypal on Feb 18 at around 3 PM and put my request in the comments to get a matched quad (they only sell duets online, so I ordered two duets and requested a matched quad in the comments). By 12 noon on Feb 20, they were already on my doorstep, matched as requested.
Anyway, I went through a truckload of various tubes in the Recto to see what I would like best. I have a set of high gain JJ's from Eurotubes in the preamp, but I've been swapping power amp tubes. First was the stock Mesa's. From there I went with a set of JJ 6L6GC's. Then I tried JJ EL34L's and a matched quad of SED "Winged C" EL34's. So, the Sovtek 5881WGC's were the 5th set of power amp tubes I've had in that Recto to try in the last 2 weeks. I had settled on the SED EL34's until tonight.
So I get to practice tonight and pop in the Sovtek's. From the moment I turned on the power and start warming up with some basic metal riffing before practice, both I and the other guitarist in the band immediately noticed the difference in tone. I think it took all of about 15 seconds before he commented "Those sound a LOT better than the other ones."
In all, they worked out perfect for the amp. I'll never understand the cardboard comment regarding their sound (how the hell does something sound like "cardboard" anyway? :lol: ). I will say this...they are a very neutral sounding tube, and that's probably what people aren't liking about them when they review them. However, that's exactly what I like about them. I could completely see why someone would have a love or hate relationship with them.
First off, they don't have the more booming bass that the other 6L6's in there (Mesa and JJ 6L6GC) did. But to me, that's a good thing. If someone wants bass that rattles walls and competes with the bassist, this isn't your tube. The JJ's will get you there, as would the Mesa's. However, I find them to have plenty of low end in an already bass heavy amp and I liked how the low end sat in the mix in a band situation a lot better. It immediately made the overall sound of the band tighter by reducing some of the sub lows in the Recto and making allowing the bassist to be a little more pronounced. Playing by yourself, it might be cool to have an absurdly pounding low end. With the band, however, I found this to be more beneficial.
The mids were pretty balanced overall in the tube. In fact, I found myself going from around 12 Noon on the dial down to about 10-11 o'clock with them in. In comparison to the EL34's, it obviously doesn't have the upper mid focus, which works great for me also because I'm a V30 user (Mesa Traditional, Straight 4X12). The treble detail was pretty clear to me. They actually seemed a little punchier than the SED's in there. Running my Maxon OD808 in front as a boost, I went from running the Tone control at 12 Noon with the SED's to 9'clock with the Sovteks. It doesn't have the sizzle of an EL34, but again...that's a feature I like about them.
Funny enough, my favorite Recto I had before was loaded with high gain JJ's in the preamp and Sovtek 5881WGC's in the power amp. After trying everything under the sun, it looks like I've came full circle to what worked best for me before. If you want a tube that's going to add sizzle or color to your tone, beef up the low end to crazy proportions, and alter the tone of your amp in some form...then this is NOT the tube for you. If you want a tube that's very neutral all around that will remain tight without imparting massive qualities of mids or bass into your sound, then they might suit you well. They worked perfect for me...twice... 8)