- inherent limitations of tube amplification technology (as explained by lexmill)
All gears have limitations, both tubes and solid state included. It's really a choose your own poison kinda thing.
- maintenance issues (total cost of ownership)
There are a couple of dimensions to maintenance:
1--Generally, tubes wear out faster than transistors, especially power tubes. So yes, in this sense, maintenance of tubes is more costly.
But if you're talking about driver tubes, those last a long, long time. The 6111WA in my DAC is rated at 10,000 hours or about 10 years of listening pleasure, never turning the damn thing off.
And transistors, capacitors, etc. in S/S wear out too. Hypertriode recently replaced the op-amps in my NAD 502 despite tender loving care.
2--Tubes generally have simpler circuitry than S/S and parts tend to be "discrete" (i.e., point-to-point wiring vs. crammed PCBs). So when something breaks (and most gear do), tubes generally are easier to repair.
3--As far as total cost of ownership goes, tubes have a distinct advantage over S/S in that there are significantly more system tuning options with tubes. If something changes in your system (say you upgrade speakers, cables, or move rooms, etc.), it's generally easier to tune the system to your liking with tubes (tube rolling, caps, etc.) with tubes than with S/S.
So instead of changing electronics also each time there is a change in your system, you just make some parts modifications and you're done.
- safety issues (for kids who may also inappropriately "touch" the eqpt)
I have a 3 year old. Safety is an issue to me.
http://www.jcaudio.com/product/AudioNote/daccomparison.html is the full range of Audio Note (tubed) DAC's.
http://www.conradjohnson.com/It_just_sounds_right/current-tube-line.html is the range of Conrad-Jonson (tubed) pre-amps.
What's there to threaten my 3 year old here?
- no practical value (sonically and economically) embarking on it
Sonic value, like beauty, is in the eyes/ears of the beholder so this sweeping general statement is careless at best.
Now economic value, well, let's see:
1--Mullard EL34 metal base sold for US$2 when it was still manufactured. A used xf1 was posted in Pinoydiophiles Marketplace for PhP7.5k ea.
2--GEC KT66 was <US$4 now US$180 ea
3--The Dynaco ST70 sold for US$100 in kit form. The sub PhP50k souped up ST70 from Hypertriode is a true bargain nowadays.
4--The Scott 299 was ~US$220 new. You'd spend ~PhP20k to buy a working one now.
Contrast these numbers to the <PhP20k my brother in law paid for an Onkyo TX-DS575 (I think, a fine model BTW) receiver 2 years ago. How much do you think he could sell that today?
Or even so called "audiophile grade" stuff like my NAD502 (~US$300 new, aorund PhP30:US$1 then) and someone else's same model for PhP5k in the Marketplace with no takers if I remember correctly.
Do please correct me if I am misunderstanding your concept of "economic" value.
As I've mentioned before jofkevski, nothing personal, OK? I'm responding to your post as these (very) hasty generalizations of yours are terribly damaging especially to newbies.