Doge 8 Clarity: 12AT7 replacement for phono stage

Hello fellow enthusiasts... My apologies in advance for the noob question.

I've put together my first all tube system, as far as preamp and amp combo is concerned. Looking to see IF replacing the phono section's 12AX7 (Mullard ECC81) tubes with lower gain 12AT7 in my Doge 8 Clarity 2017 ed. will help lower the "hiss"/ tube rush coming off with my current set up. Doge's phono setting is on MM (using Bob's Device Sky 20 SUT), Phono: 47k, tried both normal and low sensitivity, (- 8) gain reduction, but "hiss" is still audible from my seat 7' away from the speakers. 

I'm looking at replacement tubes from Upscale - Mullard 6201 which they claim to be the "quiet" ones. Not sure if it will help in lowering the hiss I've described.

Doge's line level still holds the stock 12AT7 tubes and to me - they sound nice as the reviews online says. I'm sure it can do better with tube rolling. No audible hiss from my seat. Switching between any line level onto phono input clearly augments the hiss.

To take advantage of Doge's much improved line level over the phono, I've utilized my only external phono stage - Schiit Mani. Not ideal but i can handle that better than deal with the hiss using the Doge's internal phono stage. I've contemplated on just upgrading to a nicer phono stage but that's another topic.

So, will it work to replace the 12AX7 with lower gain tubes 12AT7 to decrease hiss in my system? 

Thank you in advice for your time and responses.

Current system:
Rega P3 (2016), NEO ttpsu, DV 20X2L
Schiit Mani to line level vs Bob's Device Sky 20 to phono level
Doge 8 Clarity 2017 ed.
Mystere PA11 
KEF R3 on stands

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I wouldn't listen to the guy in that link. 12AT7 is not a substitute for 12AX7. It may be done in guitar amps but not in HiFi. The plate current of the AT7 is much higher than the 12AX7 and gain is 40% less. It's possible the tonal qualities may be affected.

The acceptable sub for the 12AX7 is a 5751 which is in the same family and is used when lower gain is desired. 

You're saying the Doge phonostage is 47Kohm which is for MM. And you're using MC with a SUT. That sounds fine, but it's possible that the circuit in the Doge is noisy and inferior to an external phonostage. I've seen this a number of times where the built in phonostage is not equal to the line stage.
IMO, you're better off using a separate phonostage which is designed for a MC cart.

If you decide to swap tubes, use a low noise 5751. As stated above, the dealer will test for noise, but you must ask for MC phono quality.

The problem I have with Upscale is that they do not accept returns. They wouldn’t even take back tubes that I didn’t use.
Brent Jessee and Andy at Vintage Tube Services will exchange and take returns on tubes. Brent answers email quickly and Andy likes phone calls. Both have a very large stock and are good guys.

Vintage Tube Services
 Call Andy.  PHONE: (616) 454-3467
He will hook you up

Good morning... thank you for the responses. What can I say? You guys are amazing here by providing info and direction...

@ tomcy6: Thank you for the link. 

@ lowrider57: As I mentioned, I'm fairly new to tubes and have not come across info on the low noise 5751s, and will definitely read more into it. Thank you for the direction. Doge is known for their excellent line level, but not much to revel about its phono stage. Nonetheless, I was being optimistic of having less ICs by using the Doge's internal phono stage. Not losing hope yet. I'll reach out to Vintage Tube and see what they say. 

@ grey9hound: Talking about making it easy... thank you for the contact info. 
"...replacing the phono section's 12AX7 (Mullard ECC81) tubes with lower gain 12AT7..."

Just to be clear, ECC81 is the equivalent of 12AT7. 12AX7 tubes have the designation of ECC83. Double check your stock tubes.   
+1 for Vintage Tube Services and Andy. I would try the 5751 tube or a 7025 tube (the 7025 is one of the few tubes specifically designed for hi fi). And if your phono stage has switchable gain settings, just use a lower setting than you now use; that may fix your problem. 
One other thing you may want to try is experiment with the different gain settings on the Mani to better match your cartridge and see if that helps reduce the noise. 
Before you try any swapping, I would look into the fact that if you have a high performance tube phono section, that its a simple fact that no matter where you get the tubes for it, they have to be hand-picked. About the only way to do that properly, assuming that otherwise the tubes check good, is to listen to them.

The Chinese 12AX7 is not bad in the noise department, which is to say that out of 100 of them, you'll probably find about 85 that are acceptable. Tubes do have a way of going bad, even new ones, so I would contact Doge and see if they can provide you with a proper replacement. 
I have had good results with Black Sable tubes from Tube Depot.  They are hand-selected for low noise and microphonics.  Andy at Vintage Tube Services is also great.  
@ kalali: Thank you for the correction. I'm the second owner of this Doge and the previous owner rolled the stock tubes. After checking the tube boxes, its the reissued Mullard 12AX7. With Mani running into one of the line levels - No issue with hiss I described compared to running straight to the phono section.

@ bsmg: I've tried different phono sensitivity setting and applying Doge's  (-8) gain reduction - still find the hiss an issue for me. I would definitely check out those tube recommendations (5751 & 7025). 

@ atmosphere: Being the second owner of the unit, I'm not sure if I'm able to avail any warranty on the unit. Without any other matching tubes around, I may have to pony up with replacement tubes to see if the phono section's hiss issue I'm having can be remediated.

chayro: Nice to learn more about different tubes. Glad to hear you had good experience with Black Sable and its characteristics. It appears everyone here are in consensus about the guys at Vintage Tube Services.

Thank you all for chiming in. Much appreciated!
Since I'm happy with the Doge 8's line level, it seems easier to just upgrade from Mani to a higher quality phono stage.... but I'm not quite ready to give up on the Doge's phono and where's the fun in that, right?

But hey, feel free to make recommendations for phono stage appropriate for my current system as described:

Rega P3 (2016), NEO ttpsu, DV 20X2L
Schiit Mani to line level vs Bob's Device Sky 20 to phono level
Doge 8 Clarity 2017 ed.
Mystere PA11
KEF R3 on stands

When i said "appropriate" to my setup, i meant each piece of my system cost me about +/- $1,000 (minus Mani), I guess I wouldn't want to spend 2 or 3 times the amount of my cart, etc. Not sure if that is a "sound" approach - no pun intended. 

Again, thank you in advance.
The quietest new tubes around are those tested, graded, matched into pairs and quads, and sold by RAM Tube Works.
I wouldnt use a 12AX in place of a 12AT. Often 5751s DO NOT work well in phono stages and would check with the mfgr before spending anything on a 5751. There are many tube sellers that check for noise and microphonics. Having said this, this service is only valuable if the test equipment is more sensitive than your application. 
@ atmosphere: Being the second owner of the unit, I'm not sure if I'm able to avail any warranty on the unit. Without any other matching tubes around, I may have to pony up with replacement tubes to see if the phono section's hiss issue I'm having can be remediated.
Warranty has nothing to do with it is my guess. We're a bit weird in that we have a 1 year warranty on our tubes but most manufacturers usually offer 90 days. So my guess is no tube warranty. But Doge should still be able to provide you with 12AX7s they know will be quiet in your phono section at some nominal charge.

Now one thing I haven't seen asked: Can you hear the noise when the needle is tracking a silent groove? If no, then the noise is no concern!
Even if you could lower the gain in your MM phono stage with a 12AT7 tube swap (which is not advisable anyways, as others have mentioned), it wouldn't help your hissssss noise floor much because the phono stage is before the preamp's volume control - so what you REALLY need to improve is the signal-to-noise ratio, rather than any absolute noise floor.

Your tools for increasing signal-to-noise ratio in your vinyl source ecosystem are as follows:
1. Get a different cartridge with higher output level. Your Dynavector's 0.3mV output is right around where these things start getting difficult.
2. Use a SUT with a slightly high ratio - you're already doing this, and 20x is a good ratio for your cartridge. You could go even higher (say 30x) to further increase signal-to-noise, but then the flip side is you start cutting closer into the MM stage's overload margins (i.e. higher distortion).
3. Don't load the cartridge too heavily, or you will lose signal, while noise floor stays the same - hence a loss of signal-to-noise ratio. With your 20x SUT, the 47K MM input, and a 5-ohm cartridge coil, you should be OK here.
4. Get a higher quality, lower noise MM stage. Easy win, if you don't mind spending the money ;)
5. Source as low-noise tubes as you can, when your MM stage is tubed. You may or may not already be near your stage's low-noise limits, with the stock tubes - only one way to find out! But in Chinese preamp w/ onboard phono, I wouldn't be surprised if they didn't take any care selecting the stock phono stage tubes. Even the better Chinese brands are notorious for shipping with crappy tubes. 
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The Schitt Mani RIAA phono amp has a "Decca" gain setting, which provides 30dB.
Of all the tube gear in a system the phono stage/pre amp section is most susceptible to tube variances. If there is ONE place to splurge on tightly matched high quality tubes, this is it! I totally agree with what others have stated, buy from a known tube dealer. Inform them that these tubes you're buying will be used in a circuit, in a tube phono stage. Best of luck. 
I have to say, you all have been great in sharing your wisdom about this awesome hobby and passion we all share. I thought I've read enough about tubes but I obviously have yet to scratch the surface per se. The last 24 hours have been very informative. Thank you all!

@ bdp24: RAM Tube Works - definitely worth checking out. If it wasn't for work getting in the way ; ) - I would've made some headway in calling about the tube recommendations here.

@ lowrider57: the brief moment i got to check iPhono2 online - it appears to be a good contender for what i'm looking for. I'll have to do some more research, and see some comparison reading between that and the DV P75 which both are under $1k and falls under my budget in case I go that route.

@ jsautter: I was actually thinking of using 12AT7 instead of 12AX7 on the Doge's phono stage which requires the latter. I will contact Doge Audio to check whether it is even feasible what I'm trying to do, or better yet, see what they have to say.

@ atmasphere: I appreciate your input and guidance. I know you're well respected in these forums. I will do the test you recommended I do, and will report back.

@ mulveling:  Thank you for the valuable tips in increasing signal to noise. Looks like I will have to really look at a good set of quality, quiet, MC phono grade tubes compatible with my Doge 8 to properly achieve my goal. 

@ robertplata: Splurging! Yes, and as mentioned above, I will have to pony up for the "right" tubes. 

I'm glad I posted this question of mine, as I was ready to pull the trigger on some tubes that I would have not been able to return. That would've been an expensive experiment. 

I have two 1960's era Telefunken blue tip medical grade 12AX7 tubes in my phono stage that I got from Brent Jessee about seven years ago. $350 for the pair in 2012 but are very nice. Using with Ortofon 2M Bronze and am quite happy with this setup.
I own a doge 8 and the phono section is quite good. I use it with a Hagerman piccolo 2 step up, a very very good one for peanuts. I have no hiss with a Benz lps.
In the phono section I use a Mazda silver 12 ax7  and other make of tubes. The man in charge of after sale service in europ who is a tube specialist recommend electro harmonix as a good cheap tube which work well on it.