I am selling two Melz 1578. Date codes are VII 75 and XII 64. They have exactly the same structure and are electrically matched despite their production codes are 11 years apart. I bought them NOS from an eBay dealer and used them like 5 hours then I sold my amp.

I tried them briefly today with Schiit FV with adaptors. The XII 64 one sometimes gave some cracking noise, but not consistently (sometimes no noise at all). I couldn't tell if it's the tube or the amp, FV was not designed for 6sn7 after all. I retest both on my Hickok 752a again. They both tested strong(750/760, 775/770, 400 is the minimum good) and life test great.

I don't have an amp build for 6sn7 anyways. Hopefully it may help others who need them. Thus, I am selling both as is at a price for one tube which also includes PayPal fee and shipping to North America.