Tube Noise Measurements (with no mention of 6CG7/6FQ7)

[velo]

It would be nice to see the 6CG7/6FQ7 in this list. He does offer a strong opinion on 6GK5/6FQ5A.

https://tavishdesign.com/pages/audio-tube-noise-measurments

 

[ruffrecords]

6CG7/6FQ7 will give similar noise figures to the other tubes tests. I am not sure why he used a 390R input termination - it seems a strange value.

No matter, it demonstrates why all tube mic pre designs begin with a 1:10 step up transformer which reduces the tube input noise due to the tube down to about 0.5dB. At this point other factor influence the EIN like transformer winding resistance. It is not to hard to achieve a theoretical NF of 2dB to 3dB. Further effort in reducing EIN is pointless because a) at most you will reduce noise by 1 to 2dB and b) because a whole range of physical construction factors come into play at such low EIN values.

Cheers

Ian

 

[rock soderstrom]

I am not sure why he used a 390R input termination - it seems a strange value.

Quote:

"The noise figure is calculated for a 390-Ω source resistance. There is nothing special about the 390 Ω; it is just a convenient value similar to the resistance of a moving magnet phonograph cartridge"