12AX7 Pinout question...

[Bob Simpson]

Why are pins 6, 7, & 8 listed on the 12AX7 data sheet as the first triode?

Should the tube be used 6,7,8 first or 1, 2, 3?

Just rotating the socket 180 degrees would accomplish this, yes?

Are different tube brands ( same tube designation ) different in this regard?

Bob

[tweedeluxe]

Rumor has it the 2nd triode is quieter.

[paulster]

Some manufacturers (can't remember which) stated in their data sheets that the construction meant that the 6/7/8 triode was quieter and should therefore be used in more sensitive circuits.

[Phil_S]

Rumor has it the 2nd triode is quieter.

And if this is, perhaps, just urban legend, let's just say this is the custom of an industry that died ages ago, and now we just live with the legacy.

In another 50 years, someone will figure out how to put tubes in a sandblock. Glad I'll be gone by then.

[Andy Le Blanc]

Standard practice once was to ground one side of the heater, so if you a standard layout,
the triode on the grounded side would be measurably quieter. Its the same with a series supply,
the ground end of the string had the valves most prone to noise. Now
measurably quieter does not mean you'll notice, may be for a record pre.
where the noise floor can be a real issue.

[Structo]

Bob I have noticed that too on some data sheets.

Which one are you looking at?

Also interesting to note that Howard Dumble used the first triode (pins 6,7, as the first stage in at least ODS #124.

So if the second triode (pins 1,2,3) is quieter, then why didn't HAD use that as the first stage?

[FuzzFaceBuilder]

I read on an old Mazda Belvu data sheet that the first triode is quieter when running the two cascaded. I'll keep an eye out for that chart though!