For this evening's random Icon HP205D musings, I will discuss the Mullard GZ34 metal base rectifier, a highly desirable 5AR4, in the Icon. Despite its well deserved reputation, I have mixed feelings about this valve. In the EC Studio B which is already very fast and dry, the metal base's characteristic crispness, energy, and fast transients push that particular amp to be too "urgent" in its delivery. I'm not a fan of very slow and syrupy DHT amps, but with the EC and metal base combination the pendulum swings too far in the opposite direction. However, and back to the subject of this thread, in the Icon the GZ34 works better as an alternative to 274Bs such as the Tak or Elrog. The Icon remains a more middle ground amp on the fast / slow (or dry / wet) continuum compared to the EC. The metal base nudges the Icon in a more energetic direction but never off balance. I think I'm going to ultimately use the Tak 274B more than the Mullard but some may well prefer the Icon's voicing with the metal base.