Is one half of a 12AX7 typically better than the other?

[1blueheron]

Is it true or is it urban legend that the back half of a 12AX7 is usually quieter or somehow " better" than the front half?

If you are building an amp, and you are using two gain stages, which half is best practice to put first in the sequence?

I have seen schematics that have done it both ways, just wondering if there is a right and wrong or if either is perfectly acceptable. 

Is it possible that using the closest set of pins in the layout is better than using a specific side first when it comes to noise?

Sorry for the newbie question and if it has been discussed ad nauseum in a previous thread, please point me in the right direction.  Not sure what term in the search engine would point me in the right direction.

[shooter]

Not sure what term

I have the same problem Google just don't understand me 

as to your ?, I'm not aware the tube knows it has 2 halves. 
layout is the only criteria I know for who gets wired how, that can be dealt with by taking your time in layout so the "A" tube is oriented as "1st"

[sluckey]

The left side is definitely better than the right side. 

[PRR]

> The left side is definitely better than the right side.

Unless you are in Australia.

No, they make a million halves, throw them in a bin, then assemble them into a half-million 12AX7.

[1blueheron]

Thank you all.  I will sleep better knowing that I don't have to worry about tubes being left brained or right brained and I don't have to design around this myth.

[pdf64]

With regard to ECC83, see p1 of the Philips info eg http://www.mif.pg.gda.pl/homepages/frank/sheets/010/e/ECC83.pdf

the triode section connected to pins 6, 7 and 8 is the more favourable section of the tube with respect to hum

[jbrew73]

With regard to ECC83, see p1 of the Philips info eg http://www.mif.pg.gda.pl/homepages/frank/sheets/010/e/ECC83.pdf

the triode section connected to pins 6, 7 and 8 is the more favourable section of the tube with respect to hum

This .     I’m not sure if it actually matters or not but the manufacturer thought so.

[pdf64]

I've not seen any 12AX7 / 7025 info with similar guidance.

[1blueheron]

I've not seen any 12AX7 / 7025 info with similar guidance.

The GE data sheet lists pins 6,7,8 as "section 1" and pins 1,2,3 as section 2.  Coincidence or the order they felt they should be used in?

I also saw a spec sheet that listed the input/ output capacitance of section one and section 2 as slightly different.

In reveiwing schematics, it occurred to me that in most (not all) of the designs where only one triode section was used, they typically used pins 6,7,8 which seems illogical until you see 6,7,8 is section 1.  If we take both data sheets at face value, any designs implement both sections should use "section 1" first for lowest noise.  I am not sure where "right/left" or "A/B" come in as they do not correlate directly to anything other than paper drawings as far as i can tell.   Perhaps we should call them starboard and port?  Lol.

Would be interesting study to see how many manufacturers observed the section 1 first rule and if those amps are generally lower noise.

[1blueheron]

Sylvania data sheet also has section 1/2  as 6,7,8 1,2,3 respectively and shows "direct interelectrode capacitance" as different between sections.  https://drtube.com/datasheets/12ax7-sylvania1955.pdf

[tubenit]

It was a proper and legitimate question and I've read the same information about one section being quieter then the other.

However, if I listed 12 things that one "should" be attuned to in order to reduce hum/noise,  this would not be on the list. 

[jjasilli]

I've noticec that numerous schematice have the b section first in the signal chain