Seeking a Warm 12AX7 Tube for Preamp

I agree looking into NOS 5751 tubes since I use a set in my preamp section. I would contact Brent Jessee for advice since he stocks many 12AX7 type tubes. He has some matched sets that are a bit over $100.

In my profile system page there is a chart for NOS small signal tube ie 12au7,12ax7 etc. its very handy for what you're asking. note its labelled 12au7 but it's the same for 12ax7, 12at7,12au7.   

OK. So I have to come clean... I made an impulse purchase. I've been enjoying THC edibles. And a few weeks ago I got an email about a Chi-Fi option. It is one of those "clones" that's based on a venerable old model who's patent has long since expired. So I bought a unit that is modeled on an old Matisse tube pre. It uses (2) 12AT7 and (2) 12AX7. I bought some new Mullard Reissues (12AT7), and I got a deal on the 12AX7 (new JJ). All from Viva Tubes.

https://www.ebay.com/itm/224885709348?var=523754766478

The preamp is shockingly well built. And sonically it is doing some very nice things. Very quiet noise floor, great open sound stage, and wonderful detail. But tonally, the balance is a bit thin, and the upper mids and higher frequencies are "shouty."  So I'm looking for something a little more warm on the top. 

Brent Jessee has Matsushita made 12ax7 that are very similar to Mullard construction for $110 matched pair. They are listed as: “12AX7 / 7025 Selected Dynascan, Allied industrial or Red Tip Low Noise Japanese made” on his website.

Otherwise, Mullard reissue should work for you.

Mullard is the gold standard of unabashedly warm 12AX7 (and EL34, and...). Even the reissues are warm, but (in my experience) vintage British short-plates are probably the warmest & thickest sounding of all. Long-plate British Mullards are still vey warm, but a little more balanced and articulate than their later short-plates.

Brent Jessee has Matsushita made 12ax7 that are very similar to Mullard construction for $110 matched pair. They are listed as: “12AX7 / 7025 Selected Dynascan, Allied industrial or Red Tip Low Noise Japanese made” on his website.

Otherwise, Mullard reissue should work for you.

~15 years ago I had a pair of Japanese 12AX7 with a very sharply angled (45 degrees) top getter & flashing. It's a very striking feature - can't miss it. I think (pretty sure) they were Matsushita. The plates may look like Mullard and be made with that tooling, but the sonic balance of these tubes was VERY bright. I used them specifically to counter an Eico HF87 tube amp that was otherwise too warm when used with vintage Mullard EL34. They might be the brightest 12AX7 I’ve had, though they sounded very good in this one context, to "balance the see-saw".