I have a completely rebuilt Eico HF-81... virtually every part and wire has been replaced with careful choices by an experienced HF-81 rebuilder I've tried 3 sets of vintage NOS output tubes, with surprising results: #1. Siemens E84L / 7320 (heavy duty version of EL84 that can sub as a 7189) - sounded OK, but mid and highs lacked life and sparkle and sounded noticeably veiled) #2. Russian 6P14P-ER (heavy duty long-life version of 6P14P that can sub as a 7189) - sounded OK, but mid and highs lacked life and sparkle and sounded veiled) #3. Russian 6P14P ("plain" Russian tubes, inexpensive) - sounded very good all around, very good highs/mids, with maybe a tiny bit less strength in the bass vs. the others so I'm running the amp now with the plain cheapo Russians because they clearly sound the best, but I'm wondering why the two other tubes -- both of which should be "much better" tubes -- did not sound as good also, can anyone suggest the best output tubes to use specifically in an HF-81, where everything just clicks and they sound really great? hoping for a best-bang-for-the-buck option, and also an option that is simply the best (but might cost more) ideally, the options should reflect tubes that can be located and purchased within reason, and have a decent expected lifespan any advice or suggestions greatly appreciated, thank you!