What are the functions of the 5z4 and 0d3 tubes.

Thanks Mlsstl for your reply. I do have a layout of the circuit that came with the pre. The 0d3 is the last to light up upon turn on but that may not mean anything. Why would this pre require two different voltage requirements. Mmmmm. It sounds really good!

Ah so that's why the glow is different than the rest of the tubes. Tell me Herman have you found any sonic differences between the various 0d3 tubes available. I did have a RCA and replaced it with a GE and found it sounding much better. I have not seen any euro tubes for this particular one and wondered if it was a US only made tube.

Thanks Herman for all the info you provided. I'll probably check on other tubes and compare with what I have now. Good listening!