Hi Kevin,
Yes that's a good sign. The AI is dead quiet with tubes in decent shape. A bad hum 'usually' indicates a bad transistor whose noise does not travel.
EH will last a bit longer, but not nearly as long as Voshkod,OTK, Rocket Logo etc.
Enjoy your AI. If you want the ability to use real NOS 6922/7308 email me or IM me.
Mitchell
I use (below) with Deoxit D5 to clean sockets. For tube pins you can use D5 BUT, it will remove the printing - been there/done that. I use very fine steel wool with denatured alcohol, dependin g upon how badly tarnished the pins are.
https://www.cvs.com/shop/gum-proxabrush-go-betweens-cleaners-wide-prodid-767370?skuId=767370&cgaa=QWxsb3dHb29nbGVUb0FjY2Vzc0NWU1BhZ2Vz&cid=ps_oralc_pla&gad_source=1&gclsrc=ds