I don't know why all these rectifier tubes are so popular among manufacturers, they are usually overpriced and don't perform as well as two 2.5 volt half wave rectifiers. I guess is because it's cheaper to implement than the 4 pin half wave rectifier tubes.
Rectifier Tube Rolling in a Modwight LS 36.5DM
I was hoping to get advice, I have been rolling Rectifier tubes in my two box preamp I am blown away how different tubes change the sound ,I own two sets of Mullard GZ37/CV378 a set of GE 5U4GB both vintage early 1960's and a set of stock Sovtek 5AR4 also have a NOS set of 6H30 DR I am trying in the clean box , both the Mullard's and Dr tubes only have about five hours of run in time but the sound seems defused on the top end ok on the bass the GE Tubes are good in the mids but soft on the highs and bass so far the stock Sovtek seems to sound best ,Dan says try 5R4-GY Tubes, any one tell me about the Mullard's in this preamp I am getting frustrated, thanks