I also own a Will Vincent rebuilt ST-70 wired in triode. I ended up changing all the tubes. RCA 7199's made a positive difference. I tried SED "winged C" el34's and a quad of Siemens el34's. I much prefered the Siemens, winged c's being too rolled of at the top for my taste.
But getting a Mullard fat base gz34 made it sound like a whole new amp. A much better amp. I actually couldn't belive what a positive impact it had on the sound. So if I had a limited budget for tubes, I'd spend my money on a Mullard gz34 first.
But getting a Mullard fat base gz34 made it sound like a whole new amp. A much better amp. I actually couldn't belive what a positive impact it had on the sound. So if I had a limited budget for tubes, I'd spend my money on a Mullard gz34 first.