@MikeWaters Here's what I did on EE.SE to fill the chat. When I closed marginal questions (some of the too broad questions, some of the off-topic questions), I would add a comment which would encourage the posted to take the question to the EE.SE chat. Both the O.P.s and the regular contributors would see the comment.

After about two years of such prompts the EE.SE chat became self-sustaining.

To save time, I had a handful of cookie cutter comments which I could paste, and maybe adjust for a particular situation.

This initiative took place around 2015.

@NickAlexeev Ah, very good! However, I'm not a moderator anymore.

@MikeWaters Even hanging in chat while you are doing something else on Stack Exchange already helps to get the chat room going.

Promotion of chat can be done without moderator privileges. You've got more than enough clout as a high reputation user, and an ex-mod too.

What amplifier class is this one (schematic) ?