Posting a FYI to those new to tubes.
It helps SQ to clean the oxidation off of the pins. I use a stainless steel Dremel wheel and automotive Mass Air Flow cleaner (or 99% IPA) with Q tips to finish. Do not follow up with any audio fool stuff like Pro Gold, etc. Most cannot stand the heat and self destruct to a messy gooey crap that is near impossible to clean out of the socket later.
Edit: this is for unplated pins like all 6S4As used with the KGST.