Converting Solid State to Tube Rectification on a Preamp

That's true.  The DC from a full-wave bridge should in theory be a bit smoother, but I doubt that would make any difference in a preamp.

What preamp do you have?  I have switched back and forth on several preamps from solid state to tube rectifier, but each of them was a DIY unit where I had intended to have this flexibility when I built it.  A commercial preamp with solid state rectifiers may not be as easy to modify.  For example, you need a power supply for the heaters of the tube rectifier.  An all solid state preamp is not likely to have this capability.  A tube preamp will already have a 6v or 12v supply which might be able to supply the voltage needed for a tube rectifier, but it may not have the current capability to handle a rectifier tube as well as the signal tubes.  If the preamp has a 6v supply and has enough current capability, you could theoretically use a 6v indirectly heated rectifier tube such as a 6X4, but the resulting B+ voltage will be lower than with a solid state rectifier.  That may or may not be a problem.

Of course, if you have the skills to build an outboard power supply for your preamp, you can basically build anything you want.  You can use a different power transformer that has a slightly higher voltage output to account for the losses with a tube rectifier, and the new transformer can have the proper voltages for the rectifier tube as well as signal tubes. 

By the way, a typical tube rectified power supply uses a dual-element rectifier tube and a power transformer with a center-tap secondary wiring.  This is a full-wave rectifier.  A solid state power supply often uses a full-wave-bridge (4 diodes) that can be fed by a power supply winding that does not have a center-tap.  This allows some savings in transformer cost.  But both types of power supplies are full-wave.  So the issue is not full-wave vs. half-wave.