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Big Bad Bob Big Bad Bob is offline
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Default Triode Naming Convention

On 2020-10-02 16:34, Phil Allison wrote:
Xtrchessreal wrote:

=======================
Section 1 is so called due to lower hum compared to section 2.


** The 2 triodes of a 12AX7 / ECC83 are identical,
one doe not "hum" more than the other.

================================================== ===

Internal connection arrangements for grids and heaters vary
between versions and brands, maybe having a small effect
on capacitive coupling if high impedances feed he grids.

It is very common to use DC voltage for the heaters to
eliminate any issues whether grid or cathode related.


Just read the REMARK on the bottom of page one. https://drtube.com/datasheets/ecc83-philips1970.pdf



** My post is *about that exact remark* - explaining it.

An *earthed* internal link from pin 9 travels past grid pin 7 in the scenario described. A link carrying 3.13VAC travels past grid pin 2.

This might inject up to 1mV into pin 2 if the grid source impedance were *10Mohms*. However, for a MM phono cartridge, the impedance is 1kohm at 50/60Hz and for a guitar PU about 10kokms.


Actually it's more like 100k for a typical guitar amp pre-amp input, but
your point is still worth it because a low impedence path on the grid
helps to mitigate the problem. The thing about the phono cartridge amp
is the RIAA curve which I believe is around 40db higher gain at the low
end of the frequencvy spectrum as compare to the high end. I believe
the curve is ~2db per octave (with some flatter and steeper spots at
transition points), which closely matches a ceramic pickup. So yeah,
low freq noise is going to be worse in this case, because it's about
20db higher than the mid-range for the phono input.

https://en.wikipedia.org/wiki/RIAA_equalization

In any case, I'd be concerned about injecting ANY low frequencies into a
phono pre-amp.