The longest you have owned any gear?

Polk Monitor 7B speakers and Optonica RP3636 turntable both purchased new in 1978. Still in rotation in my second system. 

Audio Research SP-7 pre-amp and D100 amp, and Dahlquist DQ20 speakers all bought in 1988 from Wilson Audio in New Orleans, Louisiana. Audio Research gear sold in 2017 (for 47% of original cost). Looking to sell DQ20s.

Revox A77, bought new in '72. ESS TranStatic I's, bought used in '81. Nakamichi BX300, bought new in mid-'80's. Original Quad ESL's, bought used and restored in the early '90's. Townshend Elite Rock turntable, bought new around the same time. An ARC LS-1 and Bedini 25/25, used in mid-'90's. Stax Lambda Pro Earspeakers and McIntosh MR78, used in late '90's. Still own them all.

Polk Model 10A from 1979. They're in my home theater system now. I still use a Burwen Research 1201A for filtering hiss when I dub LP's to disc. A 1977 Army purchase!

Optonica is a name I’ve not heard in quite a while! 

Its nice to go see that some people have gear that provided real long term satisfaction.