WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
Wow, now that is a question. I suspect you have not gotten response on this because it has a massively broad and subjective answer that has been covered before, currently and again throughout perhaps a billion established threads in this forum.
To address this directly would be simply too daunting I am sure, not to mention so subjective...
I suggest some hours perusing multiple threads and you will find the information there in it's most appropriate form. Good luck.
Each amplifier design as well as specific implementation has its own sonic signature, each dht type, and different brands/vintages within a given dht type also have their own sonic signature.
A huge number of permutations to deal with, no one has the definitive answer IMO.
Great results can be achieved with any of these types depending on the required power and other specific design goals.
They pretty much all sound similar to each other when the driver topology
and quality of the output transformer are kept constant. That said, you'll
hear larger subjective differences when you vary between, say, someone M6 cored gapped transformer versus some else's nickel cored parafeed transformer. You'll then hear some other subjective differences as you swap
out the driver from, say, RC coupled to IT coupled. With the smaller
tubes (2a3, 45, 845 operated as a 45), you can build a two-stage amplifier
and benefit from the distortion cancellation tricks that can be had with two stages of gain.
Requirements and budgets drive the choice. Lowthers, Klipsch, and the like can definitely budget out and build a 45 or 2A3 amp in a nice, compact footprint. 250V and 60 mA.
People with 90-93 dB efficient speakers would need more power,
and will have to build a larger footprint amp with 300B or 845 at low voltage.
450V and 70mA.
People who want to spend alot of money, presumable to drive an inefficient speaker with a SET amp, will have to build out an 845 or 211 at 1000V, at
high expense, extreme difficulty in parts reliability and amp construction.
I built an 845 amp that runs at typical 300B operating point. At the time,
845's (new) were $39/ea. I'm still running the same pair that I bought in
2003. The motive for low voltage 845 was comparative cheapness compared
to hyped 300B products, and the alleged and now confirmed long life of the thoriated filament tubes. Another motive is that the amplifier just simply looks
cool in my living room - if you're going to take the time to build something,
the build quality and materials and finish should be A+.
IF you are using a ZFB (zero loop feedback) design, then the sound is all over the map. That will vary by tube age, tube manufacture, date of manufacture and manufacturer (brand).
If you are using an amp with feedback, then that will tend to alter the results, but still there are sonic differences based on the same factors.
They are literally all different.
I'd say that the sound groups together around tubes of one type - BUT there is a big difference between "300B" tubes depending on who made it and when. Even Western Electric tubes vary depending on age (which also changes their manufacture and materials slightly).
Also, one would have to compare amps made with the same output iron and topology, and in practice that doesn't happen.
Then too a tube that sounds great in A2 with a given topology might sound like doogie poop in A1 with another topology. Same thing with the iron and power supplies.
How about fixed vs. self bias??
So the answer is simply: there is no simple answer.
Nearly all 845, 211 and similar amps use 1000V and more power supplies although I am most interested to read that the member above has built one successfully at 300B operating points. I personally would not be happy having something as lethal as that in my house although I agree that they do look really cool. If I needed that power I would definitely change my speakers. I am sure your 45 amp sounds lovely with your Lowthers.
Actually, I have a 300B SE amp and a good friend has a 2A3 Parallel SE amp with similar circuit topology. For what it is worth(almost nothing) I prefer his and if I were to build something similar(which I would not) I would definitely use 2A3's.
Only different in terms of primary impedance. The point I was hinting at is that I think it may be easier to achieve optimum results with a 2A3. Looking at the 300B curves.....well, they are pretty much perfect.
Well, bear, I use new production WE 300B's(which I got a good deal on,barter actually!) and my friend has quite a collection of 2A3's but he mostly uses NOS RCA double plate. So good enough quality in both cases,I think. I am not much into tube rolling myself although I did a little bit in the past.If I had some good 45's, I would certainly make something for them but I always use what I can easily get.Although I am not an engineer, in the engineers vs. audiophile debate I would tend to go with the engineers; I have seen too much snake oil in my life in various fields!
Sure... what I am getting at is that all of these tubes sound rather different when used in ZFB amps... I think I have a reason for it, but without some tests to back that it up it is just my personal conjecture. That's why I was curious about which tubes you used... AND, did you swap the driver tubes when comparing?
In a recent situation with a SE 845 amp (commercial import), the differences in 6SN7s used as the driver were staggering. So, what is the "sound" of that amp, or those 845s??
Both of us use 5692. Morgan Jones has done extensive testing on 6SN7 types,as I am sure you know. I recently built a unity gain linestage with balanced 6SN7 cathode followers sitting on 6P15P current sinks. Once I had debugged it the amplifier seemed to have so little sound of it's own that I did not even bother to change the ordinary JAN Philips 6SN7WGTA which I had put in just in case it blew up on first power on.