I finish my dive down the rabbit hole with ALO Pan Am, AKG Q701, and the Tung Sol 6AK5 (1949). Approx. 25 hours of time on them.
Shared an email with Dave Hollander (Arizona Tube Supply - arizonatubesupply.com
) and he explained that based on the code assignment and internal construction that these were likely manufactured in 1949.
Excellent quality tubes and service!! If you're hunting, I recommend checking with Dave for your NOS (no new production) tube needs. He's on Ebay as well.
These are fast, linear, with a smooth and slightly recessed midrange. (at least in comparison to the Mullard 5654) No grain. High frequencies are smooth and revealing. Loads of detail, though some recordings will sound slightly harsh. So, they may be too bright for some rigs. Linearity = less texture and touch for me. Bass is excellent - tight, fast and defined.
Overall character is less saturated in comparison to the Mullard 5654 and Cifte 5654. Drier, but not lean. Accurate. Complex music is presented as a coherent whole, with a well defined stage (wide) and clear spatial cues.
I really dig these tubes. They make my Q701 really fun - bass performance may be the best of all the tubes I've tried. The trade off for the linear sound is a sometimes biting high end, less texture, and so a cooler blue presence. Less warmth than the Mullards.
Gear:
AKG Q701/ALO Pan Am-Gateway/Parasound Zdac/PC/Fidelizer Pro/Roon-Tidal
Music Reference:
Deafheaven, Bjork, Elbow, Fiona Apple, Joshua Redman, Father John Misty, Charles Mingus, The Tallis Scholars, The Bad Plus, James Blake, Gary Clark, Jr., Sparklehorse, Jeff Buckley, M83, Nils Frahm, Open Mike Eagle, Portishead, Peter Gabriel, Typhoon, Grant Green, Eri Yamamoto, The Flaming Lips, Mark Hollis, Refused, Sean Jones Quartet, Spacemonkey, Throwing Snow, Talk Talk