To put it short>
I have a Reisong A10 which by now is heavily modified with mods largely based on Skunkie's design. I also replaced the output transformers to new ones from Toroidy which makes a massive improvement.
I wanted to experiment with adding SS rectification instead of using the 5AR4. The goal was to increase the B+ and keep the bias current the same by installing a larger cathode resistor on the EL34.
The result of this is largely improved sound, and I do not know why.
The EL34's run on the same current (about 70ma each) before and after SS rectification.
What I notice in sound: With SS rectification the mudiness in the audio dissappears. As if I can look into the music. The bass has cleared up and is very consistent. High frequency response impoved. I can have very very subtle detail wich are mudded before. I can reproduce this constantly.
Can someone help me understand why this might happen?
I have built my test setup in such a way that I an easily switch between the cathode resistor values needed for SS and Tube rectification. I measure the same voltages as Skunkie does with her Reisong a12 mod, except B+ gets an additional 20 volts by switching to SS rectification.
Serveral things could be at play: one, you increased the voltage across the tube which IMHO usually results in better sound in a tube amp. I design most of my amp to run the tubes at fairly high voltage. The other, as you noted, taking the load of the rectifier heater, which is right at 2A, makes the power transformer run cooler and increases it's ability to supply voltage to the B+ rail. On a SE amp, the rectifier tube itself should not impact the sound. If changing it to another type or brand does, than the power supply has issues as you have found out. So my best guess here is you have raised the voltage across the tube and at the same time removed some VA load from a marginally large enough power transformer, all good things! Would you mind sharing with everyone what cathode resistor you used? Thanks for this update!