SUPER Post on MANY counts, including the selection of Shunt Resistors. Many Thanks!My opinion only, I much prefer passive filtering. Less of a thumbprint, less parts, and less noise.
A voltage reference tube, as part of any regulator can oscillate whereas a shunt resistor will return the B+ hash to ground.
Also, there is no substitute for thoughtful use of hash chokes in tube amps, to remove noise, stabilize an amplifier, and make it sound better. Hash chokes can have a very positive effect on performance !! They often could be used to clean up the output of solid state regulators, when found in tube amps. ( eg : SP3A-1 preamps benefit greatly. ) There are more subtle ways to use hash chokes to good effect. The new 6005 prototype already has six hash chokes in it, and I now plan top add four more in a upcoming rebuild !!
A shunt resistor must be chosen for its sonic characteristic. We do have quiet and great sounding shunt resistors in 2021. My 6005 amplifier uses modern Caddock " power tabs " as the resistor to ground. ( Types MP-820, MP-930 and MP-925. ) Other acceptable shunt power resistors I use are vintage Ohmite Brown Devils, Mills MRA-12s, and ARCOL HS series chassis mount power resistors - which are engineered for pulse duty.
Back to the subject of R-Cores : Kitamura Kiden, who invented the R-Core in 1978, has McIntosh ( USA ) as a customer. We can learn about this Japanese company, who also supplies Softone their products, here :
I hope this post is of some assistance to FMs.
I am surprised about McIntoch... They have always made much that their Output transformers are all wound in house.