The reason you don't buy cheap Chinese stuff is because of the power supplies.
If the Chinese built to the same spec as good manufacturers, the prices would be about the same.
First, and most important, is the power transformer. When dealing with high voltages, trust name brand iron made by legitimate companies. I won't go into it here, but the laminations, windings and much else are very important. You do not want the cheap stuff. It might work for awhile, but it will eventually die. Good iron lasts for decades. And when you look at the potential risks, do you really want a product that shaves every last corner and squeezes every final cent? I'd rather pay an extra $40-$50 for something made by a legitimate company. Otherwise, you're just being a cheapskate willing to roll the dice for a few dollars. Would you buy mystery tires for your car to save a dollar? Same thing here.
You'll also find the chespest possible implementation of AC rectification. If they could spend an extra $2 to improve it, they wouldn't even think of it. Do you really want something that cheap?
The mantra around here is "how does it sound" and everyone wants to tuberoll. That's the wrong approach.
As for sound, most buyers have no idea what a good amp sounds like. They buy the cheapo and it sounds warm and they can get slighlty different sound from different tubes. Then they go on to proclaim that it is THE. BEST. EVAR. and that anything costing more is some kind of giant scam. Oh, and that rare NOS tubes costing 50% the price of the amp will cure everything.
That's BS. For one, the precious NOS tubes won't last as long as they should because the cheapo amp runs AC on the filaments. The average cheapo buyer has no idea what that means. It means that AC is stepped down off the transformer and fed to the filaments. AC is tough on the filaments and, further, causes the signal to vary. This is why cheapos don't sound as precise as a good amp.
It should be pointed out that rectifying filament AC into DC would cost only another $5 or so. Why don't they dpend the extra $5?
Because they're cheap amps that shave every last possible cost out of the amp.
Similarly, the power supplies are so thoroughly cheapened that you get some AC ripple injected into the B+. The solution there is to use large filtering caps and chokes. You might want a tube rectifier and maybe regulation to really nail down the voltage.
Why aren't those there? Again, shaving every last possible cost to make the cheapest possible product.
You can hear this, too. It's why the amps sound warm and fuzzy. B+ goes directly into the signal and fuzzes it out, along with the other fuzz from running AC on the filaments.
We could get into the cheapness of PCBs and how easily they're damaged and how difficult they are to repair. Point-to-point is the correct, and traditional, way to handle high voltages and high temperatures.
And yet again, the reason PCBs are used is because they are the absolute cheapest way to build.
Are you beginning to understand?
The reason good amps cost money is because most of them build the correct way and use parts that really should be there.
Cheap amps are cheap because they strip out the stuff that really should be there.
A lot of "but it sounds good" arguments are sure to turn up. But cheap amps are cheap and not worth your money.
Instead, buy solid state. No sexy tubes, but they do not run on high voltage, so you can use inexpensive transformers and use inexpensive parts for rectification and regulation. Without high power and high heat, a PCB is appropriate. Some do generate heat, but it's cheap and easy to heatsink a chip. There are no heatsinks you can thermally bond to a tube.
If you want a cheap tube amp, the best way to go is DIY. $300-$400 of parts will get you something that is built correctly and does not cut corners.
