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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



oyie2000
lowrider57's avatar
lowrider57
5,393 posts
 
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.

lowrider57's avatar
lowrider57
5,393 posts
 
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.


grey9hound
1,112 posts
 
Vintage Tube Services
 Call Andy.  PHONE: (616) 454-3467
He will hook you up
http://vintagetubeservices.com/

oyie2000 OP
13 posts
 
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. 
kalali's avatar
kalali
1,977 posts
 
"...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.   
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