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Do tubes actually sound like anything?

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My relatively limited experience with tube amps leaves me wondering if tubes actually offer any advantages.
In a well designed circuit that focuses on low distortion they seem to be transparent, in a less well designed circuit they just seem to be "less good".

I used to think the world of tubes when I bought my first tube amp but when compared to the ultra low distortion SS amps I build nowadays they don't seem to really offer anything.

I personally only make direct drive stuff in order to avoid the possibility of caps or transformers interfering with the sound, but I've noticed (again, in my limited experience) that the warm/sweet "tube sound" people seem to refer to is present in transformer-out tube amps.

The tubes I use have mainly been limited to 4p1L, 6sN7, and 6080 tubes.
Has anyone confirmed any sort of sonic superiority over "transparent" amps with tubes?
IMHO the survival of vacuum tube factories has to do with the pleasant quality of the distortion you get when red plated on guitar signals.
In the hifi market, tubes require less feedback to produce a given level of distortion, according to a greybeard on here. This allows for different levels of distorting overtones than BJT (bipolar junction transistors), which many people find more pleasant than BJT amps. More even harmonics less odds I believe is the usual explanation.
I have vacuum tube equipment from the 50's & 60's, hammond organs and dynaco equipment. The dynakit PAS2 preamp was superb until a paper capacitor went off value, then with polyester replacements it is rather tinny. I replaced 9 others before I found the one the kit builder had burned the wax case with the soldering iron. That was causing a channel imbalance.
The ST70 power amp with new electrolytic caps new rectifier & output tubes, is as fuzzy as original, when HD was 1% at full 35 w/ch on a good day. Great for 1961, not bad in 1970 when the competition at $100 was SWTC Tiger, but my SS amps sound better now. HD can be driven down to .1% or so with an alternate input structure than 7199 tubes, which are unicorns anyway.
The hammond organs are great after 185 electrolytic caps were replaced, but HD is not measured on organs.
When I heard a MacIntosh vacuum tube power amp about 1974, it was driving Klipschhorns which have a problem with non time alignment of treble & bass. The program material was light jazz combo, trumpet string bass drums, which is IMHO not difficult to reproduce. There were no cymbal crashes or tinkly bells. So I have really no idea what it sounded like. I use well recorded piano CD's to test amps & speakers, which show up defects in nearly everything. If your ears go to 14 khz as mine do, or above if you're a woman. Plus have some experience in what a great Steinway grand sounds like.
In practical matters, tube amps will not blow up a lot of expensive parts if the speaker terminal is shorted. They will sometimes short an output transformer if the speaker wire is pulled off, unless internal overvoltage protection is provided. Tubes take lightning strikes better than SS in my experience. My PAS2 & ST70 took a strike in 1982 so bad it exploded a turn off pop cap and carbon tracked the power switch to "on". It was off while I was at work. $3 damage. One Hammond organ was in a church on top of a hill north of Cincinnatti, and this is a belt with violent storms. 46 years plugged in with no protecting power strip, 2 hours/week use, the damage was 118 dried up electrolytic caps and a rubber power cord falling apart.
Best of luck in your experiments.
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The main difference is that tubes being responsive to the Child's law, the current through them are the voltage at their grid, to the 3/2 power. So they contain mainly even harmonics. SSin the other hand respond to an exponential law cheating far more odd harmonics, disliking to the ears. A 5% distortion in a tube amp is by far much more tolerable that 1% of SS harmonics. Look to schematics. Tube amp need no or few dB feedback, while SS needs lots of dB's to be supportable. A clear example is a tube radio: most of them lacks entirely of NFB. Try a humble 741 with no NFB. (Please, test it far from me).
I have only designed 2 flea watt amps with valves, but...

I believe a well designed valve amp, should be transparent, irrespective of whether it is OTL or transformer coupled output.

I also believe that dominant 2nd order harmonics in the THD is a worthy target, but not at the expense of vastly greater overall THD.

I'd rather 0.5% THD with 2nd and 3rd harmonics at equal level, than 2% THD with 2nd harmonic dominant.

That opinion, will probably attract opposition; but it is only an opinion.
Well, in my personal experiments I have been unable to tell the difference with and without excessively high levels of 2nd harmonic in the same circuit.
I also make solid state amps with unmeasurable harmonics, even and odd.
My zero GFB feedback low distortion tube amps sound pretty much the same as the SS one (at least in the limited tests I did).
As far as tubes go it's not transparency that I'm interested in.

I know they can be transparent. What I'm wondering is if they actually offer any euphonic distortion or if this just comes from transformers/PS or placebo.
I recall experiencing euphonic distortion in my early tube amp days (not overly long ago) but the same amp to me now just sounds sub par.
I did a limited experiment recently and just threw a 6SN7 with a battery bias on grid, cathode grounded, and threw a simple resistor load on the plate and played with the bias to see if I could get any euphonic distortions out of it.
It went from "okay" to "bad" depending on bias, but no euphonic distortions.

So in other words the tally of my experiences is that, tubes in a good circuit sound transparent, tubes in a less good circuit sound less good.

I have a number of really cool tube designs I made a few years back and I have some friends that want me to make some tube stuff for them but I won't bother if I can't find any real advantages in doing so.
not to mention that sound is so subjective. What seams pleasing to one persons ear may not necessarily seem pleasing to another.
For my hearing, tube gear does sound more 'natural'..whatever natural may be, in my case, more like listening to live music.
I own both, tube and solid state. I prefer tube for the reason above.
And as has been mentioned, they look cool too. Of course the cool look is utterly secondary and should never dictate the design or layout of any given tube amp or preamp, the circuit is above all else, everything else is secondary.
01A looks pretty linear, near constant Mu.
Data sheet from Franks below:

If they have some "sound" to them, it's probably microphonics, like singing in a room full of Carillons. If you like that effect, try some of the bigger frame grid tubes setting on the speaker cab.

Tube amps are just fun to build and experiment with. Fairly robust against circuit/wiring goofs. Easy to get good sound. They can be made to be transparent or euphonic by design. Parts are big enough to see, and it's possible to build an amp with fewer parts. They look interesting. Great learning experience and hobby. Lots of old books and magazine articles to check through, a feeling of history with the original pioneering of circuitry/design.


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that the warm/sweet "tube sound" people seem to refer to is present in transformer-out tube amps.

No. Using modern transformers with amorhous or nanocrystaline cores and high quality caps and resistors all this intolerable fuzzy warmth can be effectively cured. Especially with PP amps and especially when avoiding very coloured valves.

Unfortunately some valve characteristics such as microphony always remain. Getting a reasonable Df for bass reflex speakers without resorting to global nfb is also tricky.

Otoh transistors are also not easy when you are fussy :)
not to mention that sound is so subjective. What seams pleasing to one persons ear may not necessarily seem pleasing to another.

But that's nothing to do with sound reproduction. Sound reproduction is about recreating an original as closely as you can within the resources available.

Creating sound is a completely different matter. Don't get them confused.
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