Tube Parameter "Attenuation, Harmonic" What is it?

[TheGimp]

I was looking at the data sheet:

http://www.radiolamp.su/pdf/112/6/6Z9PE.pdf

for the small pentode 6Z9P-E and noticed it has a parameter for "attenuation" with numbers given for second and third harmonics.

What does this parameter mean? No conditions are listed as to how the tube is set up or how this is measured.

[Glowbug]

I'm taking a guess here, but attenuation is a reduction in signal - so the 2nd harmonic is 40dB less than the fundamental, and the 3rd harmonic is 70dB down?

[TheGimp]

That is pretty much what I figured.

However I why why it would it be specified and what relivance it has since such harmonics are normally a byproduct of non-linearity in the tube. 40dB does not seem to be a particularly great attenuation.

As a broadband amp I can see why it would be important to suppress harmonics, but would expect IM to be as improtant, if not more important.

[revintage]

Whatever the sheet says, this one looks very interesting/nice/linear at 15mA and just above 100V.

[TheGimp]

I guess I need to go ahead and build an input stage with one to see how it behaves. I'll have to rewire a 9-pin socket though. Filaments cathode and grid are in the same position as for the A side of a 6N1P so it isn't too bad.

[dsavitsk]

That's the same tube as the 6688/E180F. On ebay, they are usually listed as 6J9p, and you shouldn't pay more than about $1 each for them.

I have a bunch, and my experience is that they sound OK, but some of them develop a squeal after a few hours use, and nothing seems to be able to stop it. YMMV as I may have just gotten a bad batch. But, real 6688's don't cost a lot more.