What, measurement wise, is "tube sound?"

[mhardy6647]

Alas, on my SET amps, the tubes are turned 90 degrees so the plates are viewed edgewise from the front. I wouldn't be able to see the light show even if I bought those 2A3s.

I mean, you could reorient the sockets -- or just turn the amp 09 degrees, you know?

View attachment 136928

Even 6550's can look cool

To get this back on topic the optical coolness of various vacuum tubes should be measurable and quantifiable.
Kinda hard to beat thoriated tungsten filaments and mercury vapor regulators in this regard -- although, I, too, am a sucka for the blue glow.

DSC_0001 by Mark Hardy, on Flickr

in full disclosure, the photo above, of a very cheap ValveArt (Chinese) 2A3 of the late 1990s, was taken by my son, not by me.

 

[Wes]

I'm pretty comfortable with it. I'm, very comfortable with the idea if the error signal is -60 db it is inaudible 90% of the time with very nearly all music. I'm not so comfortable with the idea tube amps can maintain - 60 db into real world loudspeaker loads with their complex reactive impedance.

Just as a for instance most CJ amps would list frequency response as pretty flat 20 hz to 20 khz (but at low signal level). While full power specified some level of THD at full output for 30hz to 15 khz. This would have been with a resistive load. With a reactive load my guess is distortion is somewhat worse.

90% is ok, but implies a level of resolution not achieved. I usually say "unlikely" or some similar sobriquet.

Making absolutist stmts. here simply plays into the paws of Slithering Subjectivists, who want nothing more than to poke holes in claims by people who adopt an objective view of audio.

 

[dfuller]

Oh, if we're posting pictures of glowing tubes... Take 4 Tung-Sol reissue "7581A" 6L6s in my guitar amp.

Anyway, on the topic of "what makes a tube amp sound the way it does" I think it's a combination of two, maybe three things. High output impedance, limited feedback, and relatively early (but soft) onset of distortion. But it's also the spectra - tubes in a competent design (and with tubes that are in good shape, biased well, etc) generally have little in the way of high order harmonic distortion. This isn't always the case, but it often is.

 

[Blumlein 88]

The other great demo of this is Bill Waslo’s tracks of a string quartet with a hidden signal buried 60 dB or so down.

Not just a hidden signal, but a raucus brass band.

 

[Blumlein 88]

I built a unity gain cathode follower buffer for a passive volume setup I had. Later built a cap coupled darlington transistor buffer. They both sounded the same. Both had about 300 ohms output impedance and wide enough bandwidth and then some.

 

[SIY]

I built a unity gain cathode follow buffer for a passive volume setup I had. Later built a cap coupled darlington transistor buffer. They both sounded the same. Both had about 300 ohms output impedance and wide enough bandwidth and then some.

Here's mine from some years back.