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RE: Recs. For 12AX7 Low Noise Good Sounding Tubes

Posted by AbeCollins (A) on September 7, 2011 at 09:39:14

In Reply to: Recs. For 12AX7 Low Noise Good Sounding Tubes posted by AudioSoul on August 7, 2011 at 05:27:49:

I've been researching and testing new (not necessarily NOS) 12AX7 types for my Aesthetix Calpyso linestage. I can hear different amounts of hiss with my ear up to the speaker's tweeter depending on the 12AX7's I have plugged in. Some produce louder hiss while others I can barely hear at all.

I could be wrong, but I don't think you are guaranteed to get a "low noise" tube just by selecting a particular NOS type. My lowest noise tubes are the ones that I specifically requested to be low noise when I purchased them from sellers who have the ability to test for noise.

My two quietest pair of 12AX7's are:

- JJ Tesla 12AX7 "Black Sable" hand selected "Gold" noise grade then Cryogenically treated. Bought from TheTubeDepot.com

- Mullard 12AX7 CV4004 British NOS, hand selected for low noise. Bought from UpscaleAudio Kevin Deal.

Others that were noticeably less quiet:

TJ Full Music 12AX7 from Parts Connexion.

Sovtek 12AX7LPS from TheTubeStore. One is noisier than the other but neither are as quiet as the JJ Tesla and Mullard above.

Tung-Sol reissue 12AX7 from TheTubeStore.

For my application the slight bit of hiss from any of these tubes is not an important factor as I cannot hear any hiss at all from my listening chair. However, it was interesting (for me anyway!) to note the large differences in the amount of hiss these tubes produced with my ear up to the speakers.

I would imagine that the hiss issue is much more important in a mic preamp or phono stage. I would also guess that your chances of getting a truly "low noise" tube is a crap shoot unless your seller is able to test his batch for the lowest possible noise.

I would also guess that if you bought 1/2 a dozen or so new tubes (maybe Sovtek 12AX7LPS), you're likely to find some that are noticeably quieter than the others. I bought a pair of Sovtek 12AX7LPS, one ended up being very quiet and the other not so quiet. And this is just from putting my ear up the speaker. ;-)

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