Get the low noise 12AX7 tube directly from CAL. Costs about $35.00, but by far the best option IMHO. The other thing that helps with those is to upgrade all of the connectors from the crappy board mount style to the thru the bulkhead types. CAL has the connectors available for $60 for all 3. Did this to a unit I own and the changes were simply astounding. Takes about 2 hours, but if you are capable, the change is well worth the cost. I have been through tubes from Kevin @ Upscale, the 12AX7LPS, NOS.... I have spent more on experimentation than I did on the original hardware, but the stock CAL Low Noise tube is best (IMHO).
What tube for a Sigma dac?
Looking for suggestions on which tube to use in my Sigma 24/96 dac. My system:Sony 7700 dvd, CAL Sigma 24/96 dac, Morrison pre, Odyssey amp, and Magnepan mmg's. Someone mentioned a Raytheon nos 5751 or a Mullard nos 12ax7. Current tube is a Ruby 12ax7. Regards, Brad