Hi my WBFellows! ...
I can't try, nor can I afford, all the 274B and other rectifier tubes that have been reviewed by this group - but I have tried the KR5U4G (that came with my Horizon), Takatsuki 274B, Sophia Electric Aqua 274B (not Aqua II), Ken Rad CKR5U4G 1943 NAVY, Tele RGN2004 smooth plate, Tele RGN2004 silver mesh (circa 1932) and, finally the Tele RGN2004 black mesh (circa 1930). All the older fella's are NOS and some NIB. All, except the KR and Takatsuki, were compared with the Mullard ECC32 in the "converter" seats and SFR P.17C in the "power" seats of my Horizon because they are my preferred dual triodes and pentodes. The pics below show some of the other pentodes I've tried and loved.
The top 3 Horizon rectifier tubes to my ears and for my system, in ascending order, are the silver mesh RGN2004, Ken Rad CKR5U4G and, at the top of the heap - the black mesh Telefunken Klangfilm RGN2004. All are really good because they share the same characteristics and attributes: well built, reliable, play well with others, and help the dual triodes and pentodes in the Horizon reproduce music in a very real, analog-like and holographic manner with wonderful tone, proper pace and stunning transients. The oldest Klangfilm, distinguished by black mesh plates and bespoke production techniques (note the serial no. is embedded in the glass stem) betters the other two in realism, articulate bass, tempo and ethereal holography. In short, this 93 year old has the skills and energy of Leopold Stokowski conducting the Philadelphia Orchestra in Disney's Fantasia.