You would have to ask Sophia if it will work in all 300B circuits. I'm not familiar with the tube.
What are the sonic differences between ss or tube rect. ??
SS has more punch in the bottom end. The tube rect. is slightly warmer in the midrange.
What are the sonic differences between the 'optional' black gate caps or the standard 'ultimate'.
Not much difference in the DRD circuit.
What etc. between the copper or silver trannies for the above kit.
I haven't heard the silver trannies in the DRD yet, so I couldn't comment on the differences you might hear.
Ron
