I realize this is a very old post but I put some late 60's NOS Mullard EL34's in my Quicksilver Mid mono's that had the stock Tesla's in it. There have been a few things that have got my attention when trying out new "so called" improvements to my system. This was one of those "holy @#&*%" moments when I thought the price of those tubes was well worth it. A VAST improvement.
Ruby el34s sound flat?
I just put a new quad of Ruby EL34s in my Quicksilver Mid Monos. The highs are limited, the sound stage is smaller and it just sounds veiled. Is this just a bad choice for this amp or do they just need to "break in"? Previously I had Teslas. I am using Gallo 3.1's