Then what is a consumer supposed to know and what do I have to be vindictive about by simply posing the question to someone in the industry who avails himself to these forums.?!
@faustuss You could start by doing better research before making untrue statements. Just say’n. Here’s another exampe:
why wasn’t it designed for the AC powerline voltage available at the time
It was. The longer answer is when it was designed we often saw +120VAC in many parts of the country. 117V has been on the low side for a very long time.
Usually, the manufactures claims of full output into those loads can’t be verified because of the limited amount of current available from the wall outlet (real world).
IMO, anyone doing measurements that doesn’t have a way of dealing with that isn’t playing with a full deck. Get a variac for heaven’s sake! Then you can insure the line Voltage is correct by doing measurements.
We ran into that problem with our MA-3 which makes 500 Watts. It has AC line correction to deal with brownouts and can make full power even if the line has dropped below 100VAC.
I don’t have to adjust bias on my tube amps for years and if it’s a set bias amp I don’t have to think about it at all unless I notice a degradation in sound
That’s usually the case with our stuff too.
Then there’s the question of whether if loading an OTL’s outputs into resistors has any proven sonic merit over having the outputs of a conventional tube amps into an output transformer which I believe is one of the aspects to the widespread attraction to the way tube amps sound.
I hope you really didn’t mean this. Who loads OTL outputs into resistors?? Resistors don’t make sound and aren’t loudspeakers... so don’t expect to hear anything when you do that. If you meant something else, either your sentence is poorly constructed or you have some sort of misconception about how OTLs work. I can’t tell but you mentioned this twice...
WRT to output transformers you have a variety of challenges and they are not a source of widespread attraction. First is they have limited bandwidth- the higher the power the more limited they get. Somewhere in the 60 to 120Watt range is about the upper limit for what might be considered ’hifi’; IOW full power from 20Hz to 20KHz.
Its an excellent transformer that has bandwidth to 5Hz; most are specced to 10Hz. Distortion will rise in the amplifier as the frequency is decreased towards the cutoff. This is very measurable and interferes with bass impact, messes with midrange clarity as does the phase shift that accompanies. Of course if you are after high power, the ability to play bass properly may mean that the highs will be limited.
The next problem is the sigmoid curve of hysteresis. It distorts the signal in its own right and also causes the load line of the power tubes to be somewhat elliptical. If you don’t know the significance of that, look it up! Its gets much worse for series feed SETs where the output transformer has a gapped core! If the load line is elliptical the power tubes will be making more distortion and all output transformers result in some elliptical behavior.
If there is a mismatch in the power tubes, that will appear to the transformer as a DC component. This can cause the transformer to make greater distortion.
You can compensate for a lot of this with feedback of course. However, there is an upper limit where the poles and odd resonances of the output transformer limit how much feedback you can use before you have stability problems. To correct for some of that of course there is lead and lag compensation (the former is that little cap in parallel with the feedback resistor... the latter a network usually seen at the output of the Voltage amplifier).
A very skilled designer can deal with that though but that will mean a very expensive carefully designed output transformer, both of which can be counted on one hand. The best example of that is likely the KrohnHite UF101 which employed up to 80dB of feedback which was quite a feat!
OTLs allow for much wider bandwidth with high power and since there are less poles and zeros (since there’s no output transformer), much higher feedback can be used if desired.
OTLs do have their downsides, but you didn’t mention them other than the number of tubes used.
FWIW, if you have no need to check the bias on your amps over years of use, either you really don’t use them all that much, you are doing yourself a disservice or they are auto bias, which is something we’ve employed for about 21 years. We didn’t automate the DC Offset since it is trivial compared to the correct bias setting, and since we have a VU meter on the amps it can serve multiple duty as it allows you to see the relative output power of the amp, see if the tube condition has changed and can even be used to test the power tubes with the right procedure.
The reason tubes are on borrowed time is several factors all happening at the same time.
The first is that class D is slowly invading the musical instrument amplifier market. We have several in our studio right now. Guitar amps are a much larger tube market than high end audio! About 80% of tube production goes to guitar amps. When a 100 Watt guitar amp weighs only 15 pounds as opposed to 85 pounds, people notice that when they are moving out of a venue at 3:AM. These days an awful lot of guitar players get their ’sound’ from effects pedals rather than the ’sound’ of the amp as was common in the 60s and 70s.
So as that market fades it will be harder to maintain production at the same levels! The market is going to look a lot different in 10 years.
The next problem is the effects of Covid and war in Ukraine. That has driven tube prices up all over regardless of the country of origin. Russian tubes are only allowed into the US from Russia because Mike Matthews of New Sensor in NYC owns some tube factories in Russia. Otherwise its hard to get Russian stuff and they were one of the world’s larger tube sources. So when a tube factory in China burned down a few years ago, suddenly JJ was on the hook and could not keep up with sales. Prices skyrocketed. We’re paying 3x what we used to for output tubes. 6SN7s, 12AT7s, 12AU7s and so on are all a lot more expensive.
Tariffs have not helped matters at all. They will not be the reason anyone starts making tubes in the US again. Forget about RCA or GE bringing tubes back 
Finally, class D amps have evolved to such a state that they now can be as smooth and revealing as the best tube amps, without the issues of heat, reliability and size. Why would you want to run tubes if you can get the same or better sound quality for less money and bother? The only real answers are not for sound quality; just for fun and nostalgia (which is perfectly legit), seeing how someone was able to do the art of tubes by making an amp look cool. If those things are not important but sound quality is, then there are class D amps that are a better deal and a whole lot easier to live with.
I should point out though that class D amps vary in sound quality more than tube amps do, so if you’ve not heard the right one or ones you may well be wondering what I’m talking about!
So yes, tubes are on the way out. I realize back in the 1960s they were declared ’obsolete’ and have now been around longer as such then when they were the only game in town. But technology does march along, so even though a declaration in the past was proven false does not mean that will always be so.