Which NOS tubes on my ASL 1009 for more warmth?

Lapierre,

Isoclean or HIFI Tuning fuses?

Why recommend the HiFi?

Glory I have both Isoclean and HiFi Tunning fuses.

The Isoclean fuses are in my McIntosh amps (yes it made a difference.) The HiFi tuning fuses are in my Emm Labs CDP and preamp. I could not find the exact replacement fuse for my preamp 1.24 in Isoclean so I had to use HiFi.

I was planning to spend approximately $400 on a quad of Mullards and a bit less on a quad of 12au7's...but that depends on how much difference they make. Where would I see more noticable improvement? I bought the amp used I'm pretty sure the caps were upgraded by an ASL technician.

FWIW, you can probably get a fair change/improvement with different 12AU7's compared to the stock Chinese tubes, but before I went there and before I would spend any big money for NOS EL34's you might buy some of the best new production EL34's, such as SED's, and see if that is a big enuf improvement for you. At least they are a great benchmark tube, sonically and ruggedness. Once you have those in place you can do some simple experiments with 12AU7's to find a good match.

Most of your sonic improvements should be with the 12AU7s. You can purchase Mullard EL34/6BQ5 New Production for $25 (matched pair)and save $350. Evaluate your system as Newbee suggested and determine the 12AU7 that best match your system. Plus, you have a lot more 12AU7s to choose from to refine sonic characteristics of your system.