Additional Preamp Tubes

+1 on the Mulllard CV4003.

My favorite 12AU7 variant.

  You have nice gear and premium tubes. My experience with 12AU7’s in a line stage pre brought me to Telefunkens. I’ve tried a few American tubes , the German stuff and regular nos Mullard 12AU7’s. The Seimens Nickle were too bright and the Mullard sounded like a blanket over my stereo. I ran Tungsram’s long ago and they were somewhat relaxed. If the CV 4003 is above the standard nos Mullard , that might be good. NOS Tung Sol’s are nice. The nos Tesla is similar to Tekefunken but a pinch more relaxed. FWIT people absolutely rave about the Mazda’s. I’d suggest asking PS directly and Andy at Vintage Tube. Also Brent Jesse’s site is still up and the descriptions are very accurate. Happy Hunting , Mike B. 

@mofimadness Thanks, I will probably try them. If I knew I could trust Valve Tubes out of the UK, it would be a done deal. 
@buellrider97 Thank you. I agree, the Siemens are bright. Tele’s are a little forward. i don’t think a blanket would be good, but I do want warmth. ChatGPT once described my ref 3’s as ‘brutally honest”.  My tubes are the only tuning in my perhaps analytical system. 
I believe the CV4003 variants (both Brimar & Mullard) are military spec. Thank you for the advice. 

BTW, ChatGPT (not the end all be all… but interesting) ranked them as follows: 

Overall

1. Brimar CV4003 ⭐⭐⭐⭐⭐

Your benchmark.

2. Mullard CV4003 ⭐⭐⭐⭐⭐

If you want maximum warmth and romance.

3. Amperex Bugle Boy ⭐⭐⭐⭐½

More lively, still musical.

4. Mazda/Cifte ⭐⭐⭐⭐½

The connoisseur’s choice.

5. Telefunken Medical ⭐⭐⭐⭐

More neutral and precise.

6. Siemens Nickel Plate ⭐⭐⭐⭐

Fast, open, less warmth

Maybe investigate the nos Tesla ecc802’s . They have less treble and more mid and bass compared to the Telefunkens. I have a pair of Hammond labeled 12AU7 Mullards. PM me if you want to try them I can mail them to you. Cheers , Mike B.