Tube amps - what 3 things…

Excellent point Ralph!  Properly executed ultralinear topology is stunningly impressive.  When executed properly, it is another reason why fixed (manually adjustable) output tube bias is essential, in order that output can be optimized for ultralinear topology.

So many short cuts are available in tube (well actually any) amplifier design that it is impossible to find a commercially available one that doesn't employ any of them.  For example: does any manufacturer use an inductor filtered power supply instead of the much cheaper (and lighter) capacitance filtered power supply?  None that I know of.  The only way to get an absolutely uncompromised tube amplifier is to specifically requests such a build from a highly knowledgeable designer/builder, which will result in a very expensive and very heavy amplifier.  

I'll refrain from exclaiming how extraordinarily special the amps I use are other than to state that they are the result of such a request.

Tubes can be intimidating to start with all the different design approaches and care that is required for speaker matching. Once you start it can be addictive.

Push/Pull (I don't like really hot amps)

Don't spend too much on a tube amp. Some chinese companies (not all) are making excellent tube amps with warranty/ repair centers in USA

Include the cost of the better NOS tubes you will want to roll in

Better electronic components beats fancy features

For example: does any manufacturer use an inductor filtered power supply instead of the much cheaper (and lighter) capacitance filtered power supply? None that I know of.

@xenolith As far as I’m aware, chokes are always used in tandem with capacitors. If you know of a topology that uses only inductors, I’d love to learn about it (Google failed to find any such thing). We’ve been using chokes (inductors) in our power supplies for decades and we are by no means the only one- the use of chokes seems to be pretty common IME.

FWIW, if the amplifier is class A and also ultralinear, you won’t need any adjustment since the correct bias can be automatically obtained using a cathode resistor. Regardless of the transconductance of the tube, if the cathode resistor is correct, the tube will always operate in the A region.

Of course, if you want to manually bias the circuit and run a bias supply (and no cathode resistor) you can, but the tube will be set at the right/same current anyway. One thing that will happen though is that as the tube ages and the transconductance drops off, if you always set to the same current the tube will be over-biased in time.

Ralph, stated another way, if the grid voltage remains constant as the transconductance changes, the current in a bipolar [CT] transformer will be unequal.

Seems like a greater evil... unless one is OTL 😉