What about the internal IR losses of the original vacuum tube? The
regulation should be
nearly the same if done right.

Pete

yes, but why having it the same if one can get it better

Tony

However, it should be noted that supply voltage regulation will actually
decrease if you use diodes, rather than be improved.

Here is an example. Let us assume we have 100 volt primary and 100 volt
secondary, and that the normal rectifier has a 10 volt voltage drop. We
replace the tube with 2 series diodes, which have a 1 volt total drop and
then add 9 volts of zeners. That gives us a 10 volt drop, equal to the
tube. Now, assume there is a 10 volt drop in primary line voltage.
Secondary voltage is 90, less 10 volts, which is 80 volts. The output
voltage has dropped by 11%, while the input voltage has dropped 10%. If we
still had the original tube (or a diode and resistor), then the 10 volt
primary drop will result in 90 volts on the secondary - but the voltage drop
will be fairly linear across the tube (and resistor), so will only be
probably 9 volts. Resulting voltage out of the power supply is 81 volts
rather than the 80 volts using the zener diode. In that case, primary
voltage drops 10% and seconddary voltage drops 10%.

In this special case, we have created a deregulator.

73, Colin K7FM