Phono stage: lower noise 12AX7 replacements?

[xoundmind]

Hi

 

i have some unwanted hiss in my system, which  I have isolated to the phono stage. I have some 9 month (age of the phono stage) old JJ 12AX7s in there now, but I don’t think it’s indicative of a problem with any of them.

 

If I were to swap in some 5751s or 7025s, which would likely be better for a phono stage?

 

Thanks

[Schu]

can you use a U or T in that spot?

[xoundmind]

That’s an open question. 😀

 

my cursory reading on the matter indicated the other two are good choices. 

[seti]

I'm using a quad of 12AX7 bugle boys. Have trried mullards as well. Could be anything really. A phono stage designed for 12AX7 should be able to do so easily...

 

 

[thebes]

I do believe the 5751's have a lower mu (whatever that is) and therefore should be quieter.

[moray james]

http://www.worldtubecompany.com/mm5/merchant.mvc?Screen=TF-2

 

https://www.effectrode.com/knowledge-base/the-12ax7-tube/

 

https://www.bassgearmag.com/new-low-noise-7025-vacuum-tube/

 

Although commonly known in Europe by its Mullard–Philips tube designation of ECC83, other European variations also exist including the low-noise versions 12AX7A, 12AD7, 6681, 7025, and 7729; European versions B339, B759, CV492, CV4004, CV8156, CV8222, ECC803, ECC803S, E2164, and M8137; and the lower-gain low-noise versions 5751 and 6851, intended for avionics equipment.

In European usage special-quality valves of some sort were often indicated by exchanging letters and digits in the name: the E83CC was a special-quality ECC83. In the US a "W" in the designation, as in 12AX7WA, designates the tube as complying with military grade, higher reliability specifications.

The 'E' in the European designation classifies this as having a 6.3 volt heater, whereas the American designation of 12AX7 classifies it as having a 12.6 volt heater. It can, of course, be wired for operation off either voltage.

[Tarheel TJ]

You might try rolling in some different 12AX7s before switching to a different tube type.  I have found significant differences between modern Chinese production tubes and NOS western tubes.  I had a phono stage that had a lot of tube "rush" to it.  Swapped in some 70 year old NOS tubes and the problem vanished completely!  YMMV.  I have no experience with JJ12AX7s.

[jimjimbo]

IMO JJ tubes are unreliable and poor quality.

 

You should NOT use a 5751 in a phono stage as it has 30% lower gain.  You need that gain in a phono stage.  The 7025 is a much better choice.  You should also try 12AX7 from Telefunken, Mullard, Amperex, and RCA (black plate).

[xoundmind]

Many thanks for the advice. 

[jimjimbo]

2 hours ago, xoundmind said:

Many thanks for the advice. 

If you need tubes, let me know.

[xoundmind]

2 hours ago, jimjimbo said:

If you need tubes, let me know.

I thinking about these; $15 from tube depot (and I just need three). 

 

https://www.evatco.com.au/the-new-eh-7025/
 

have you tried them? 

[muel]

8 hours ago, jimjimbo said:

IMO JJ tubes are unreliable and poor quality.

 

You should NOT use a 5751 in a phono stage as it has 30% lower gain.  You need that gain in a phono stage.  The 7025 is a much better choice.  You should also try 12AX7 from Telefunken, Mullard, Amperex, and RCA (black plate).

Oh good point about the 5751 in a phono!    Never tried the 7035 but I liked all of the rest in the phono stage and was partial to the Telefunken.   You won't find any for 15 bucks though.

[jimjimbo]

1 hour ago, xoundmind said:

I thinking about these; $15 from tube depot (and I just need three). 

 

https://www.evatco.com.au/the-new-eh-7025/
 

have you tried them? 

no I have not.  At that price, give them a try.

[xoundmind]

Well, I replaced the JJs in my phono stage with those 7025s and I actually like the tone a bit better. Having said, that did not get eliminate any of the hiss.

 

After trying every imaginable combination of tube vs solid state for phono stage, preamp and power amp, it’s pretty clear that the culprit is phono with my PrimaLuna Prologue Four. I swapped in some newer 12ax7s in that and that didn’t help at all.  
 

Maybe the transformers in the amp don’t like phono? 

[hogwylde09]

For a total black silent background, I had resort to something better. If you are handy with a soldering iron and a bit creative. Look at the CNC MM for moving magnet or the other MC phono amplifier. Boards available already assembled or DIY. 
Lots of threads about it on Audiokarma. 
Phone stage in my C-20 just too much noise. Tube rolling helped but didn’t get me there 

[EMRR]

My benchmark experience was in restoring three RCA broadcast consoles, needing 24 total 12AY7 tubes, 6 in high gain positions needing lowest noise.  I did 40 hour burn-in of about 36 tubes using the lower gain preamp channels, because they were multiples of the same circuit, and another reason I'll come back to.  I then made noise measurements of the lots and marked the boxes.  I found an overall noise variation of about 20db, and these were all new tubes from the same lot.  Most fell in the same tighter window, about 6dB variation.  The 6 quietest went in the high gain channels, the next best into the low gain channels, at which point they beat the noise spec in the manual by several dB.  

 

Back to the burn-in.  On the first 2 passes I also put tubes in the high gain channels, which draw much higher current.   I found those tubes were much noisier after burn-in, and no other position changed their noise level.  It seemed to be a permanent effect of the burn-in conditions.     Had I just loaded new tubes and gone for it without taking measurements, noise would have been worse than spec.  

 

For most people, finding a tube dealer who does reliable and applicable audio noise tests on tubes is worth the extra cost.   Unless you have a burn-in bank of some sort, you'll spend forever rolling the dice.   

 

On trying other tube types with different gain levels, remember lower gain does not mean lower noise.  It may seem lower noise because there's less gain amplifying the front end noise.  That may serve the purpose, but it's apples to oranges.    If you want to be sure of preamp noise, short the input.  If the noise goes away, it's coming from the source, not the preamp.  

[Marvel]

On 7/19/2020 at 7:47 PM, EMRR said:

 If you want to be sure of preamp noise, short the input.  If the noise goes away, it's coming from the source, not the preamp.  

 

^^^^^ This!