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Replacing 12AX7 to 5751 for pre-amp

Does anyone try NOS Sylvania 5751 replacing 12AX7 for preamp? My friend convinced me trying 5751. I did try them for Dynaco PAS 3 and woo sound is warmer, treble is softer special with vocal. Bass is more tighten than before. I want to try more AU7 or AT7. Do they ok to try? I know that we can replace any 12AX7 with other lower current.
sanjose_audio_guy
tomcy6's avatar
tomcy6
2,582 posts
 
You can't substitute 12AU7 or 12AT7 for 12AX7. There are many 12AX7, 5751 or 7025 that you can try. Good Luck.
flemke
596 posts
 
I have tried all the 5751 tubes in my 834p phono stage and found the Eat 12ax7's are superior. Not cheap,but the best.

Tim
vonhakemarine
55 posts
 
Be aware that you could raise distortion issues with certain circuits by this 12AX7 / 5751 substution. While electrically it may be benign, it is no assurance of optimum sonics. This info courtesy of circuit designer Ron Cornelius via Audio Classics concerning research on my Mac C-22. Good Luck
racamuti's avatar
racamuti
362 posts
 
I'm not sure but, I believe that if you swap 12ax7's out and put in 5751's in a "phono" preamp that it will change the RIAA curve. If someone knows for sure I would like to know.
sanjose_audio_guy OP
28 posts
 
Thanks for your information. From my taste, 5751 is my choice than 12AX7. For AU7 or AT7, I want to try but I need more advice on my PAS 3. I do not want to get risky on my preamp. Anyone already tried AU7 or AT7 for 12AX7, let me know the sound
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