I've tried the RCA 5R4GY with the light brown base. It was not in the same league in the Modwright PS 9.0 power supply as the Phillips 5R4GYS, RCA 5U4G black plate, and Mullard GZ32 5V4.
I will post the results once I've tried the Tung Sol.
I will post the results once I've tried the Tung Sol.