View Single Post
  #11   Report Post  
Posted to rec.audio.tubes
Phil Allison[_4_] Phil Allison[_4_] is offline
external usenet poster
 
Posts: 499
Default Triode Naming Convention

Big Bad Bob wrote:

==================
Phil Allison wrote:
Xtrchessreal wrote:


** 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,


** The source impedance is what matters, and is as I stated.

Guitar PUs and phono PUs are both low value resistors at 50/60 Hz.


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 frequency spectrum as compare to the high end.


** The RIAA curve boost gain by 16 dB or 6.3 times 50/60Hz compared to mid frequencies. It also boost tube noise by the same amount.

There is NO audible supply frequency hum caused by stray C *inside* a 12AX7.

The OP has misconstrued the comment on the data sheet.


..... Phil