Quick test on a EIMAC JAN-8165/4-65a NOS. Here is the THD response at output level of +22.22dBu:
Artefacts at 50Hz and above are all a result of a poor filament power supply 🙂
Nice to see this valve providing 0.14% THD at a low operating point: Ia=85mA, Va=246V. At least this is a nice test to show how linear this valve it is.
