Audiophilepure

https://www.headfonia.com/eufonika-h22s-review/

The H22S uses a 6080 power tube and a 6N8S input tube. The big advantage here is that these tubes are easily available everywhere, and they won’t break the bank if you stick to the “normal” tubes.

The 6080 is a tube that is very common in OTL headphone amp designs, and it can be replaced by a multitude of tube equivalents such as 6N5P, 6N13P and 6AS7 (+ all equivalents). Some of the more exotic and famous tubes here are the 5998 (Tung-Sol), 2399 (Chatham) or the Bendix 6080WB graphite plates which come in a whole lot of variations.

The H22S came delivered with a winged Svetlana 6N13P tube, which certainly isn’t a bad tube, though it also depends on the amplifier. It’s a perfectly fine tube to start a tube rolling journey with. An easy and affordable first switch can be a 6AS7G black plate from RCA, just to name one.