First up is the metal base Melz made 6SL7.
And the test LPs were Charlie Byrd Trio: Charlie's Choice and Stan Getz's Jazz Samba.
I usually have a set of run of the mill inexpensive nothing special RCA 6SL7 tubes burning away. I know how they sound as I spend hours listening to my setup. I'm also familiar with these records. They spend a good amount of time on my turntable.
My RCA tubes:
So how did they stack up against the RCA? The difference was pretty drastic. First let me say I wasn't expecting them to outshine what I have. I choose my hi-fi tubes carefully. If I don't like something it goes in my box to sell to guitar players.
The Melz has impressively low microphonics. Great for my phono stage. Sonically they are far more aggressive than my RCA. Very forward. Stan Getz's sometimes harsh tenor sound gets harsher, not in a bad way, just more in your face. I find the RCA tubes to be more clear and relaxed. Since I don't listen to much metal these days, the Melz tubes will go back in the box. I like to relax in my tiny universe.
I bet these will kick some ass in a guitar amp. I do have one Magnatone that used the 6SL7 tube. I have a new RCA in right now and prior to that I had a Sovtek there which I didn't find sounded objectionable at all. I have a feeling the Melz will melt some faces. I didn't find it objectionable for my hi fi either, I just prefer the RCA.
A word about 6SL7 tubes. The big octal 6SL7, 6SN7 tubes are my favorite for hi fi. They relax more for me than the more common and sought after 12AX7, 12AU7 which are obviously more in demand and more valuable. I built my own preamp to use 6SL7 tubes in the phono and line stage, 6SN7 for the cathode follower driving the power amp. I do not covet any vintage or modern preamps. I built mine 20 years ago from a Swedish schematic called "Remus". It's a fantastic circuit! Simple and honest. No Marantz 7 for me, this sounds better to my ears!
Ok next. A tube I'm really picky about. The 6SJ7. My 45 power amp uses these as a driver stage. Also my favorite guitar amps use these, Magnatone Varsity and "B" amplifier of my own design. They have something psychedelic about them, a shimmer, when in a guitar circuit. I thought it was an Echoplex I used to have but that's gone and that characteristic is still there on my recordings. I don't get it with other amps that don't use these.
So I have the fancy 5693 red RCA 6SJ7 tubes in mine. I love these for hi fi, guitar I prefer the standard 6SJ7. I have a set of metal base Sylvania 6SJ7s that I rejected in this circuit after 10 minutes. I missed the warmth and euphonic quality of these red tubes:
So I got these Russian babies. Cheap as a bag of fancy chips. No joke. A couple bucks each. How do they stack up?
I wasn't hopeful. But....they are pretty damned good! Again more forward and aggressive but not like the 6SL7 tubes. The sound was nice and round, not cold or harsh like my Sylvania tubes. In a pinch I would gladly burn these up. There is no markings on these, just a #7 in a box on the side. Charlie Byrd's guitar sounded nice and round, the percussion deep and warm with a nice top end. No, they don't beat my RCAs, but they don't offend me one bit either.
So, hope this was helpful! I will try these out in my guitar amps and do a bit about that as well. And remember just because something doesn't work for me doesn't mean it won't work for you. Give these a try if you are curious! I'd love to hear your impressions.