Is your tube amp really a tube amp?

There are no tube rectifiers that can handle filament currents.

So if one is to use DC filaments the most often used technique is to use some sort of semiconductor. This is still considered a tube amp/tube preamp. In the old days (1950s) selenium rectifiers were used, for example in the Dynaco ST-70 and PAS-3. Those are tube products and are not considered hybrids.

yes... but you'd need a massive dropper resistor to get the voltage down to heater voltage levels.

FYI - A tube rectifier is the tube equivalent of a diode, rectifying the AC into DC.

Is this thread really 2.

You can add AC for the heaters as a requirement for an all-tube amp. Otherwise you need solid-state diodes for a DC supply.

Using tube rectifiers and regulators in the power supply instead of solid state equivalents is also considered by many tube purists as being required for a pure tube design.

I would venture a DHT SET, probably the simplest tube circuit, would qualify in most cases as a true tube amp using your criteria. The fact that SS devices may be used in a given circuit doesn't necessarily mean that that it is in the signal path. So to me a true tube amp is one that uses an output tube to amplify the signal to the speakers whether SET, OTL or PP. One could argue an OTL is even a more purist design in that there is no output transformer in the signal path. As to which approach is more purist does it matter but only the end result? Each approach has it own inherent limitations in one manner or another. The other factor is the output tube used as this too can determine what we will hear.