Project Horizon

Forgot to update: The GS60 power supply solved the issue completely!

For me Horizon, with the right tube, is superb. I particularly like E80CC tubes and dual 6J5's, but biasing requires a bit of patience-once you have the correct bias both tube types can sound glorious.
Good luck in your tube rolling.
Oh, I like those 'Mouse Ears' as well, they are still good value, though more expensive than a couple of years ago.

The SMSL Sanskrit 6 has a WM8740 DAC chip .
There is also the pro version which has the 4490 chip.
These 2 chips are not far apart in performance, the 4490 can go a little higher in sampling frequency.
I see no profits (only downsides) in going above 24/192.

The Shitt modi (non multibit) also has the 4490 chip.
The modi multibit has different chip.
Measurement wise the 4490 chip is the better one.
That is except for 'noise levels
In order to make these noise levels audible you would have to listen at 150dB SPL peaks though.

But it is not as much about the used DAC chip but more the implementation.
What filter is used both digital as well as analog.
What is the accuracy of the analog filter compomenents.
This may result in a wide range of measurable differences.
Some bordering on audible ones, some inaudible and some quite audible.

The Modi MB is measurably rolled off in the upper treble.
Depending on your age and used music this may well be audible on 'direct comparison'.

When someone held a gun to my head and told me to choose between the MB and 4490 I would choose the 4490 variant.
This decision would be based on measurements.
The measurement differences are well below the 'audible barrier' for most people.

I think I would be perfectly happy with the SMSL.

Nope only 6SN7 which is exactly the same as 12SN7 except for the heater voltage.
Only the Solstice can use 12SN7

Nothing unsafe about it.
The heater just seems to work on 50% undervoltage.
It may just provide enough heat to loosen some electrons.
Not designed for it though.

The 12V setting doesn't really create a 12V heater voltage.
There is only a 6V heater voltage available in the amp.

What the jumper does (for 12V noval tubes) is use different pins for feeding the heater.

In 6V tubes the heater is connected between pin 4 and 5 and is 6V
With 12V tubes the heaters (2 x a 6V heater in series) with a centertap on pin 9 is connected differently so both 6V segments are fed with 6V.

The 6SN7 has one heater which is 6V
The 12SN7 also has one heater (no centertap arrangement) which is 12V.

So the tube will light up but not as bright as it should.
Obviously still hot enough that the cathode emits some electrons.
Just enough to drive the circuit in this case.

Nothing is going to break.
Power tubes should never be used with an undervoltage but in this case that is no problem.

No need to pre-dial the bias to any point.
Nothing gets damaged when the bias is set way too high or too low.

Sorry, I'm late to the 12SN7/12SX7/6SN7 party. Definitely my fav tube party.

I have a few 12SX7s and many 12SN7s - and a G1217 Solstice which can supply a true 12V heater output with a jumper change. Which is how normally I use it. However, in the interests of sonic science and plain curiosity, I just ran a couple 12SX7s and 12SN7s with the jumpers in the normal 6V position as if it was a 6SN7.

And all the tubes worked. One sounded pretty good - a GE 12SN7, however, all were noisier at 6V compared to 12V and didn't sound as good at 6V as at their native 12V heater voltage.

From this single data point, we can conclude that while the 12V versions of 6SN7s will work at 6V, they won't work as well.

Although usually pricier than the 12V brethren, there are many great 6SN7 tubes. For headphone listening I find the open spacious presentation of a good 6SN7 preferable to the smaller, more constricted presentation of the children's miniature tubes.

For most of my listening I prefer 6SN7/12SN7s to the little noval tubes, even the E80CC - one of my fav 9pinners. In my chain, Presonus FSM SPDIF > Mimby > Solstice > 650s, the Tungsram E80CC is very good - on a par with the best 6CG7/6FQ7s. (6CG7 is the same 6SN7 plate design squished into a smaller tube - for cost-cutting reasons, not better audio behavior from what I hear and have read.)

Out of the 6CG7/6FQ7 I've tried so far, a NOS 1950s Westinghouse and a 60s GE JAN are good 6SN7 step-children. The former preserves most of the addictive spaciousness of a good 6SN7 with excellent details and the GE has great clarity, but more forward presentation with a little less spaciousness. Haven't yet found a 6CG7/6FQ7 that bests a good 6SN7/12SN7 overall - except for marginally lower noise and letting the LED glow shine through. So far much prefer the 6CG7/6FQ7 to 12BH7A - which are too up front and harsh for my delicate sensibilities. LOL!

I have one NOS RCA 12SX7 that is exceptional - the clarity and detail of a top-tier 6DJ8 with the relaxed, open 6SN7 presentation. However, the differences between a $6 NOS Canadian GE 12SN7 and a $35 GE 12SX7 weren't worth the cost - especially since my best example of the $6 12SN7 is quieter and little more detailed than the GE 12SX7.

One thing I've learned with these 60+ year old tubes - some have aged better on the shelf than others - not to mention the differences between factories and production runs. Many used 6SN7s can suffer from microphonics - doesn't bother me too much for headphone use tho. And with the larger RF gathering plates can be more sensitive to modern RF devices in the vicinity. A simple RF modesty screen can keep those bad waves out tho. ;-)

In my experience, the 12SX7 designation doesn't guarantee elevated performance  - each tube needs to be heard in-circuit and some have greater synergy than others. And that is part of the fun of tube rolling. Discovery and happy surprises. Or slightly less happy ones.

The other fun part is selecting a tube to suit the listening session mood. And the 6SN7 family has so many unique flavours - to me a larger variety of differences than the 12AU7 or 6DJ8 types and usually at lower costs since the better 9pins are priced to match audiophile-infatuation-inflation. The 9pin genre seems to me to be about finding the ultimate 'sound' usually at an ultimate price. Not so much about enjoying the tube rolling journey as reaching the audio-nirvana destination. For me, savoring the journey is the more satisfying destination.

Want darker, smoother, wider? Grey glass RCA from the 1940s or NU Black glass. More bass and depth? Sylvania 6SN7GT from the 40s or a '52-'53 Bad Boy. Feeling airy? Tung-sol Mouse Ears or Canadian GE short base/tall glass. Lush transparency? Sylvania VT-231. Rich and vibrant with a juicy 3D midrange? Tung-Sol round plate from the late 40s or Brimar round plate. And on and on in other enjoyably audible ways.

Careful with the round plate habit tho - it can be pricey. Although with some searching and patience, a pair of Sylvania round plate 6P5s for $30-$40 and an adapter can come close to a good $200+ TS RP 6SN7 - with a wider soundstage perhaps compensating for losing a little juiciness.

The great value of the G1217 amps is not just their great design, build quality and value. Instead of just passive listening with my previous solid state amps - swapping tubes has altered the process of listening to a more active enjoyment of the music and sonic characteristics. Without the obsessive audiophiliac neurosis side effects.  I'm a better, active listener now. Hoping if I swap enough tubes, I'll become a better person - just like Jeremy said I would.

G1217 hybrid amps are so much more fun than a SS amp, even far more costly ones, that can only aspire to one sound - boring.

And that concludes my 6SN7/12SN7 party rant! Thanks for letting me wax on and on....