Some good folks encouraged me to look into the 6SL7 tubes a while back, and I'm glad they did. I just finished the first prototype - it uses the new 2U format which I'm going to stick with going forward for whatever I'm building - it allows me more flexibility with the power supply, as well as the addition of a Jensen balanced out (in addition to the Jensen DI) - the balanced out was another thing some folks recommended that I'm glad I tried. The Jensen balancing tranny is pretty $$, but I think it does add a bit of sonic mojo. I also added a mute switch (there ya go Frank! ) since I had a bit more real estate on the front panel - it also allowed me to use my cool stove knobs which don't fit on the 1U. Some initial thoughts and impressions.... I can see why folks like these tubes - kind of what I was hoping them to be. They are big and bold, but have a nice softness to the initial attack, and a very musical character to them. The tone is big and weighty, and they seem to impart the "all tube" vibe, even when running SS power. This circuit follows the current iteration of my original design which has a tweaked gain structure compared to the original five I've built thus far, but I did make a fair amount of changes to the gain structure and EQ based on what I thought would work for the 6SL7 front end, as well as some tweaks to the power section to keep heater-to-cathode voltages in spec. With the lower gain, I voiced it a bit wider since I can get away with it - the EQ is the same as my other builds with familiar shelving bass and treble, and dual inductor driven low/high mids (200Hz, 1.5 kHz). The 6SL7's make it a different beast, but it's not a total departure, and I think folks that generally prefer the 6SL7 would still dig the other design too. Gain range is great - plenty of clean range, and a beautiful overdrive with things cranked. The OD is very useable, and has a nice soft nature compared to the 12ax7's. The gain of the 6SL7's seem about ideal - 12ax7's can be a bit too much, the 12au7's sometimes not quite enough, and the 12at7's are a bit lacking tonally IMO. Plenty of output through the unbalanced and balanced outs, I'm diggin the beefed up power supply that the 2U allows me. The bad - my NOS Tung Sol is noisy - got some background waterfall, static, and occasional wierd microphonics. I hope TC Tubes takes it back, because it was supposed to test premium. The RCA is great so far, and it should be for the $$$. Other bad is I don't have any spares on hand, so I'm going to order some new Tung Sol reissues - hopefully they will be good. I don't like screwing around with NOS anyway. The only negative I can see to this whole deal is having to sort through tubes which I don't have the patience for. Hopefully I'll have some here mid week so I can give things a proper workout. Haven't tidied things up yet, but here's some proof: I'll get some clips up as soon as I get the new tubes in.