6or12SN7 Universal Dual Mono PreAmp

(5 customer reviews)

$549.00$699.00 US

SKU: N/A Category:


The Universal 6or12SN7 Preamp is a Dual Mono Design that can play any 6SN7 or 12SN7 ever made, including the original lower spec’d 6SN7GT, like the Famous Sylvania “Bad Boys” from the 1940’s and 50’s.  No magic or complicated circuitry is required to switch the filament voltage from 6v to 12v, all you do is plug a 7v or 12v SMPS in!  Switch Mode Power Supplies are those bricks we power our laptops with.  And best of all SMPS’s put out DC.  And using DC for the filaments (aka heaters) is a great way to reduce the noise floor in a preamp.

We’ve carefully selected every part and component. From the Solen coupling capacitors to the solid Cherry Wood Plinth and Hand Brushed Aluminum Top Plate, to the Universal Voltage Dual Secondary power transformer.

The Preamp comes as a Full Kit that includes all parts and an unfinished Solid Cherry Wood Plinth and Finished 3/16″/ 5mm Aluminum Top Plate. Or as a Light Kit, without a top plate or wood plinth, for those of you who’d rather build your own enclosure.

Build Information will include a Color Schematic of the Power Supply and Preamp, also a Build Series of Videos will be available on YouTube starting in mid December.  The videos will be the Build Manual.

Sound Signature:  Warm Rich Detailed Sound with Lovely 2nd Harmonics                                                          Excellent Stereo Image & Soundstage

Sample Audio @ 24/96 WAV

System Compatibility:  Main System Preamp, with lower gain it will drive most power amps to full power, however if your power amp is difficult to drive (low sensitivity) the E80cc Preamp would be a much better choice.  A perfect design match for the Yuri Monoblock

Build Complexity:   Medium – if you already make stuff, and are a thoughtful careful person, who can focus for an hour – You Can Build this Kit Amp.

Shipping Extra (to check on rate, make an account, place item in cart and go to check out page)

Discount Codes – don’t work on Kit Amps – the margin is too tight to offer discounts.

Not included:  Tubes, SMPS, IEC power cord, solder


Universal Design Can Use Any 6SN7 or 12SN7
Universal R-Core Power Transformer
Household Voltage (100 – 240vac)
Dual Mono
Input Sensitivity:  1.6Vrms
Gain 5.74
Signal To Noise Ratio:  55.8 dB / 79.4 dB@1KHz
Input Impedance:  96Kohm
Output Impedance:  1.14Kohm
Power Consumption (preamp): 3.6W
Power Consumption (SMPS): 7.6W
Tubes:  2 x 6SN7 or 12SN7 GT / GTA / GTB


6or12SN7 Tubes

SMPS (switch mode power supplies)

IEC Power Cords


Full Specification Sheet

Frequency Response

Frequency Sweep

Top Plate CAD Drawing

Power Supply Schematic

Amplifier Schematic

Build Videos – follow along with Jim on YouTube as he guides you through the build process step by step.  Universal 6or12SN7 Preamp Build available as soon as a Test Builder signs on.  The Link is to the very similar E80cc Kit Preamp Build Series – which shares the same chassis, layout and power supply.

Recommended Tools:  Link to Tools in the Store*

Temperature controlled solder station (I use: Lonove 926LED III available at Amazon)

Electrical Solder  63/37 tin/lead rosin core 0.8mm/.031” (Kester “44” 24-6337-0027)

Rosin Soldering Flux (I use: Caig “no clean” paste RSF-R39-2)

Volt/Ohm Meter (CAT III 600v – minimum) c/w probes & clip-on leads

Variac  0-130vac/20A or 0-260vac/10A  (helpful but not required)

Hot Glue Gun – a mini craft type will work just fine

1/4″ Socket Wrench & Deep Sockets 3/16 &  7/32″ c/w  3″ (75mm) extension

*Wire Stripper

*Solder Sucker

*Needle Nose Pliers

*Side Cutters

*Ratcheting Crimper (Note: this is NOT your standard red/blue/yellow crimper)

*Mini Hot Air Gun (very very useful)

*Mini Utility Knife

*Mini 1/8″ Slot Screwdriver

*Torx Driver T15

*Hex Key 2mm

Fun Fact:   The 6or12SN7 Preamp started out as a prototype designed to play both the 6SN7 and 12SN7 tubes, giving access to the more affordable 12v version of the 6SN7.  And it sounded really good, but it couldn’t safely play the lower spec’d 6SN7GT’s.  So I completely redesigned it using the original Sylvania Data Sheet for the 6SN7GT and voila the Universal 6or12SN7 Preamp was born!




5 reviews for 6or12SN7 Universal Dual Mono PreAmp

  1. Bernie F.

    My compliments to MTK, I hardly know where to start, everything about this preamp is such a pleasure, from the beautiful sound to it’s looks. The preamp is so well layed out and proportioned, you can tell how much care and thought went into it. Both the inside and outside are a joy to look at.
    The sound stage is impressive, not just the size but the space between the musicians and the realism of it. The artist are more present, in the room with you. I forget that I’m listening to speakers, they’re not even a thought anymore, I just want to listen to music, one track after another.

  2. marchunter (verified owner)

    I couldn’t stop listening as soon as I fired it up.
    I had a wonderful time building the Universal Preamp and learned a lot. It was so fun I couldn’t stop and finished ahead of Jim’s instruction build. I had a couple hiccups but they were of my own making and easy to fix because of the thoughtful layout. My hiccups were also very instructional. A wonderful experience.
    The sound is where you really get paid off for your labors. All terms you’ve heard apply here. Soundstage, separation, warm yet focused. It’s all here and you built it yourself!
    I can’t recommend this kit highly enough.
    Thanks guys

  3. Mike Baron (verified owner)

    I appreciate the time Mellow Tone Kits took with this design, creating an affordable great sounding preamp that we all can take advantage of. Anyone considering this preamp should be confident that the kit is a joy to build with great instruction, and the sound truly improved my system. In my case that is pairing with the Willsenton R8 using the preamp input.
    Clarity and imaging with sound stage improvements were my first impressions and I could not stay away from higher volumes – yes I heard new instruments come out on some of my favorite tracks that I have listened to for years.
    I plan to pair this pre up with a solid state amp for my next nirvana endeavor.
    Thanks Again!!

  4. Tedsid (verified owner)

    This was a great kit for a first timer. Because I was late to the test build I benefited from all the updated tips.

    I had one issue when I was testing the power. I had no output from the transformer, or very little. I had all my power in but none out. I started from the very start of the power chain and discovered I had somehow broken the neutral jumper wire that goes from the power input to the switch.

    With the little extra white wire left over and the extra spade terminals in the kit I was able to make a new wire and all is well!

    I listened for hours last night. I had to sit there and let track after track play from a playlist I have, play through. Every song was more enjoyable and I even ended up turning the music up a little louder than I usually do due to the quality of the sound.

    Right now the preamplifier is driving a little 5watt class A amplifier that Nelson Pass gave to me right from his workbench!

    I used to have an Ocellia preamplifier(passive for digital, tube active for phono) and 300B monoblocks.

    The system now sounds the best I have had in all my years of playing.
    And I have had everything from Atmosphere, McIntosh, Rogue, Bryston, Quad, NAD, Mastersound, Vfet Sonys and others.

    Like you say, the tubes ARE the amplifier! And I still have some Tung-Sol “Mouse Ears” to try out!

    There is something special about having built something yourself that makes everything all the more sweeter, but without your great kit and videos, I would probably not have tried to build my own preamplifier.

    Thank you again for the gift of sound and reward of building something myself!


  5. Justin Frakes (verified owner)

    First, the build of this kit was on the easier side for a Kit Amp. I did make one error by getting a tube socket off by one pin but that wasn’t due to bad instructions. Jim was very clear in the video on how to keep from making this error and I simply reversed my socket while marking it. The error was caught during final inspection so no harm no foul. The customer service provided was second to none, when fellow test-builders found shortages in white wire length and nuts, replacements were sent immediately without question. I did not have the shortages but had spare inventory from my Yuri builds.

    This preamp is a tube rollers dream as one can adapt the sound to taste depending on the tubes used. I critically listened with the following tubes:
    #145 Sylvania JAN 12SN7GT
    #247U Sylvania 12SN7GT “Bad Boys”
    #250 Tung Sol JAN 12SN7GT “Mouse Ears”
    #154 RCA 12SN7GT
    #246 CBS Hytron 12SN7GT
    #1b Sylvania 6SN7GTB
    #138 Canadian GE 6SN7GTB
    With all of the tubes the sound stage width was very similar in my room varying less than about an inch or two. The imaging was good to excellent in all cases. The differences I could pick out distinctly, were mainly the low to mid bass presentation (toms and snare in a drum kit and male vocals) and in the details (think cymbals shimmering and things like finger snaps or claps.) In some cases the separation between the singers and instruments had more “air” to my ear but it’s hard to explain. The Universal Preamp was also Dead Silent. With it turned all the way up to “11” there was nothing coming from my highly efficient Klipsch Forte III’s.

    For non-critical Rock-N-Roll listening I’d go with the #246 CBS Hytron 12SN7GT. You trade detail for more mid bass muscle kind of like a loudness button from the old days (a great match to my Klipsch speakers.) while listening to Tools “Chocolate Chip Trip” the drum solo section leapt from my speakers and literally had me pumping my fists. For critical listening when you want the most detail, go with the #250 Tung-Sol JAN 12SN7GT. In this case the bass is more neutral and less visceral; however, the clarity of the details more than makes up for the reduction on bass. In Michael Jacksons “Billie Jean” his finger snaps sounded like Mike was in my listen room! The best mix of detail with bass presence were any of the Sylvanias with the #1b 6SN7GTB very slightly edging out the other two (these are my most broken in pair so that could be a factor.) The bass was much better controlled but still present, more like what live drums sound like. The Sylvania family had a very nice “calming” effect on instruments that can be very harsh with other tubes; for example, the harmonica in Chris Jones/Steve Baker’s “Soul Storm Comin’.” I love this song and the record, but if poorly reproduced the harmonica can induce fatigue very quickly. My final litmus test for comparisons is Jackson Browne’s “Running On Empty.” My fathers favorite singer/song, so I’ve heard it about a million times during my life. This live recording comes alive in my system with the Sylvania’s, I just wish my dad was still here to enjoy it with me.

    I wanted to compare the Universal Preamp to my old Schiit Freya + using the same tubes so I swapped and compared the 6SN7’s I have on hand. The sound stage was narrower on the Freya, still wider than my speakers but noticeably less enveloping. Imaging was close but details took a back seat to the Mellow Tone kit. Not quite a “blanket” over the sound but both sets of tubes sounded better in the Universal Preamp. I think the dual-mono design of the universal preamp is contributing to this phenomena (but what do I know.) The Freya + also had a strange tone present in all of the listening I did. Almost like the low-mid treble was pumped up, i had never noticed this in my previous listening to the Freya + but in a back-to-back listening session it was very apparent. Thinking it might have been because I was using XLR connectors from my DAC to the Freya and RCA for the Universal, I swapped cables and the tone was still there. The Schiit is a fine preamp (more so with a tube upgrade) with a lot of connectivity options and could serve anyone well. That said, if the options of the Universal 6/12SN7 Preamp cover your needs AND you have a DIY spirit and want to learn how your audiophile equipment works I’d strongly suggest giving one a try. Its also a relative bargain compared to the Freya at $300-350 dollars less.

    For my review I used the following equipment:
    Raspberry Pi running RoPiee (controlled with Roon)
    Tidal Streaming
    Schitt Modius DAC
    Yuri Mono-Block Amplifiers
    Klipsch Forte III speakers
    All cables DIY using Mogami cable and Neutrex connectors

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