12au7, second triode as the first stage is best?

[momo]

Hey all,

I remember some post about using the "second" triode first , starting with pin6,7,8 as the first stage.
Something to do with proximity of the heater filaments and the noise it induces.

The original ValveCaster and subsequent circuits all use pin 1,2,3 as the first stage .
Now see the below data sheets, they all mention pin 1 to be the plate of what they call the "second unit".

So I'm thinking that the way to go is using pin 1,2,3  as the first stage, (which is called the second unit), as this is the best way to go for less noise?

[FSFX]

I think a lot would really depend on how you wired the heaters, That is whether you run them in series or parallel, whether you used AC or DC. If running the heaters on AC then it would be affected by how the centre tap was used and if running on DC it would depend on what end of the heaters (i.e. what pin) that was connected to ground and what was connected to what may be a noisy DC supply.

[merlinb]

If it's DC it really doesn't matter

[FSFX]

I did say that the specific wiring would affect the result if there was noise on a DC heater supply.
Of course, if the supply was absolutely clean, which many are not, then it won't matter.

[GibsonGM]

Why not make the DC clean (filter)?

[FSFX]

I thought the point of this thread was to discuss the possible reasons for wiring in different ways and the reasons why some may be better than others.

[momo]

This planning is part of my Valve Caster build that I also incorporated a modified Supreaux Deux circuit.
I'm using a regulated 14vdc 1A wallwart that does not even unload much when in use, so I get 19vdc for both circuits.
I send 12v regulated to heaters in series, 19v on the plates!
This being said, my main focus is on noise reduction to a max.
I even omitted using nice old carbon comp resistors just to save on noise.
So my question was me wondering if it was good to do the above.

I'm using pin 5, ground pin 4. Of course if it helps I can send 12v to pin4 and ground 5...
anyhow, thanks for the input.

[GibsonGM]

I thought the point of this thread was to discuss the possible reasons for wiring in different ways and the reasons why some may be better than others.

Well, it is....but if the DC is clean, does it not stand that there then would be no difference, and thus no reason to prefer one triode over the other?  If it makes a difference with AC heaters, great, then now we know.

I know that when I build a tube preamp circuit, my DC is clean as a whistle; I can't imagine where it would matter, but seems if the DC is clean I shouldn't be 'forced' to use one scheme over the other, the wire routing and all  (shrug).     Nobody is arguing with you, FSFX...we are tossing around ideas and thoughts.