2 Questions on tube replacement

Yes, I am usually hesitant to make such bold comments. :-) 

The 7025’s can be icing on the cake if you can find them. I used to get mine on Ebay. Agree with the comment about the gain on 5751’s being potentially problematic. My previous Muzishare x7 did not like those.

But wait… there still may be someone that adamantly claims something to the contrary. 

Wow! Question answered and help provided within 3 posts. I am impressed.

Thanks to both of you. @jjss49 I have enough now, but may reach out when I need the next set!

@yogiboy covered the important points

just be careful with the lower gain 5751's -- don't mix them with standard gain 12ax7's, or you may get weird imbalances in the circuitry

btw, i have many many nice old stock 12ax7's collected over the decades, feel free to pm me if i can be of help

1-yes

2-no

All these tubes can be substituted for a 12ax7!!

Direct Replacements

1. ECC83: This European equivalent of the 12AX7 is virtually identical in terms of electrical characteristics, mechanical dimensions, and heater requirements. It provides a seamless transition and is often used interchangeably in audio equipment.
2. 7025: This is a high-quality, low-noise version of the 12AX7 that offers improved performance in terms of reduced microphonics and hum. This tube is an excellent choice for audio equipment that requires low-noise operation.
3. 5751: Another directly replaceable tube with slightly lower gain than the 12AX7 (approximately 70% of the 12AX7’s gain). This tube provides a slightly different tonal characteristic, making it suitable for those seeking a cleaner, more transparent sound.
4. ECC803S: This is a premium, long-plate version of the ECC83, known for its exceptional sonic qualities and high reliability. This tube offers improved microphonics and stability, making it an excellent choice for demanding audio applications.