Amplifier circuitry-4 ohm vs 8 ohm

Implied, but so far not stated specifically, is that the output tubes of an amplifier need to see a high load of several thousand ohms (the exact value depends on the tube and amp design.)  If you run an output tube straight into a speaker, whether 4 or 8 ohms, it looks like a dead short to the tube -- not good. 

And, straight from the tube, one is talking an output of up to hundreds of volts. Also not good for the speaker, which wants a lower voltage, but more amperage. 

We've been flying in the face of this for nearly 50 years making Output TransformerLess (OTL) amplifiers with a direct coupled output.

Somewhere along the way I realized that the distortion of the amplifier is also the 'sonic signature' that almost any amplifier has. So that meant if you could build a solid state amplifier with the same distortion spectra/signature, it would sound the same also. That proved out to be true.

So there are now solid state amps that allow you to leave the tube world behind without missing them for anything.

@atmasphere 

I've looked at many tube amplifiers. Interested to know which solid state amplifiers achieve the same goal as tubes?

@atmasphere -- I understand that OTL tube amps have been around for years, but they are their own thing, with specific design considerations and tube selection, typically needing multiple output tubes to get the needed current. You just don't take a tube amp with transformers and hot-wire around the output transformers. 

But, you already know all that! Many others don't. But, OTL amps weren't really the focus of this discussion.

I've looked at many tube amplifiers. Interested to know which solid state amplifiers achieve the same goal as tubes?

@emergingsoul In my experience, not very many! But I am playing a class D amp at home that has the same distortion spectra as you expect to see in a tube amp. It is at a lower level however. Most solid state amps look distinctly different when you look at their harmonic distortion.

@atmasphere 

And there in lies the challenge.

I believe tubes represent a more even profile of the harmonics, elevating the harmonics in the upper range better than solid state.

So the richness of tubes and benefits of improved gain at lower levels makes them very attractive.  However, powerful tube amplifiers generate a ton of heat and this is disappointing.  It's like having a portable heater unit set to low continuously while you operate a tube amplifier, as I have learned. Unfortunately most of us don't live in a room with very high ceilings which would be a great place for heat to be accumulated without impacting the humans.

Maybe A more efficient speaker would be more desirable when working with a tube amplifier that uses less watts. ie, Full benefit of tubes without all the heat.

Hopefully I got all this right