Tubes, tone, and old age.


FWIW, just a short story about how things can change. 30 years ago I had two high power tube amps with SED KT88's. Bought a backup set (or two). Sold amp. What to do with tubes. Nothing, I just put them in a big drawer. Pulled them out every few years and always found them powerful but a tad bright. Never got an amp which served them well and I kinda forgot about them. 

I got old. Needed new KT88's. What the hell, I pulled out the old SED's. Interestingly (to me at least) the upper frequency retained its clarity but what was bright in yesteryear, now matched the natural loss of some high frequencies in my hearing due to age. Hog heaven!  

Point, if any, to this story is when you go out to buy tubes don't forget that the sound of tubes can and will vary because of the hearing of the seller as well as his knowledge of how they will sound in your system. 

newbee

And on a related note, what measurements - if there are any - show the difference in sound between SS and tubes?

Could one see this on a frequency chart?

I suspect that this is one of those areas where measurements tell us very little.

And on a related note, what measurements - if there are any - show the difference in sound between SS and tubes?

Could one see this on a frequency chart?

Yes. Look at distortion vs frequency- if it begins rising much below about 10KHz you will have a brightness problem since higher ordered harmonics will be higher than the THD suggests.

The other thing to look at is the distortion profile. Smoother sounding amps have a greater degree of 2nd and 3rd harmonic than amps that tend to sound bright and harsh. This is simply because the 2nd and 3rd in the latter amps is insufficient to mask the higher orders. Our ears interpret the higher orders as harsh and bright using the same metrics that cause tone color in musical instruments.

Start by looking at the distortion profile of an SET. That will give you an idea of the relationship of the 2nd and 3rd harmonics to the higher orders, so you can start to see what you're looking for in the measurements.

BTW you don't need the 2nd harmonic- the ear treats the 3rd very much as the 2nd as long as its not too profound. But it needs to be more profound on a percentage basis than the succeeding harmonics in order to mask them.

We've had the tech to measure this stuff for about 30-35 years but the understanding of the significance has been lagging. So we now have a direct link between measurements and what we hear. Unsurprisingly, these measurements can be a bit hard to dig up...