Professional Tube Testing
Both tubes tested Strong NOS (110%+ nominal mutual conductance) and tightly matched on a reliable and recently calibrated Mercury 2000 tube tester with the following result (mutual conductance in uMhos and percentage of nominal):
Tube 1: 15,000/14,500 (120%/116%)
Tube 2: 14,200/14,500 (114%/116%)
Good tubes start around 7000 and new tubes (incl. NOS/NIB) 12,500 - 13,000, and Mercury 2000's rated mutual conductance (nominal) for new tubes is 12,500. Test result can also be seen in the pictures. In case you wonder what all these numbers would mean to your sound experience, it's actually quite straightforward: mutual conductance directly translates to a tube's ability to amplify sound so the higher the numbers the stronger.
Appearance & cosmetic condition
Beside the world-class sound characteristics, we treasure this quad also because of their excellent condition of inscriptions - nearly 100% of the paint and lettering is well preserved and the IDENTICAL Tesla Czechoslovakia date codes are also perfectly visible on all tubes:
FG (March, 1969)
Tesla tube date codes can be looked up here: https://tubes-store.com/article_info.php?articles_id=5.