What, in your system, have you owned the longest?

A NAD 4020A tuner, bought new in 1981.

A pair of Proac Studio 1s from the mid-90s

A pair of Threshold T-50's.

PS Audio DirecStream DAC

Equi-Tech Son of Q Balanced power conditioner.   15 years .   Has served me well.    

Have set of Stax SR-5 headphones that I bought in 1975.

McIntosh MR1700 Receiver - 1978

PSAudio GCC 250 that was moded as new. My original intent was to have it replace all my separates and simplify my life. Alas, it was not potent enough for my big room, so I moved it to my TV system

dynaco a-25s bought new in 1972

dynaco dynamo a-25s bought new in 1972

MIT interconnects from the mid 90s and I think my PS audio extreme speakers cables too. 

Quantum Clip from PWB, since 1999.

Walker Proscenium TT from 1996.

While not the original two pairs of DCM Time Windows I had back in 1977, I am using a pair of late-production TW -1A's. Again, found on eBay in excellent condition!

My LP's. Then my Revox A77 Mk3, bought new in '73 (from Walter Davies, then the owner/operator of a 1-man hi-fi shop in Livermore, California, more lately the developer of the Last Factory line of LP/tape/CD care products). 

A few years ago I found a nice example of the earlier Ariston RD11 on eBay. This first version is virtually identical to the Linn Sondek. It has the long arm-mounting board and red power switch on the front left. Plinth is teak, while the LP12's are afromosia. Underneath, the same stamped steel keel and 3 spring suspension with Sorbotane foam. Two piece massive alloy platter driven by a low-torque AC motor. I added a vintage Fidelity Research FR29 arm and a Sleeping Beauty (Coral 777) lomc cartridge. And a black-anodized magnesium platter mat.

Burmester 961 speakers in 1996.
Michélle 

Ariston RD11S bought new in 1977! Still in use! It has had a variety of arms - and cartridges - on it. In order: SME 1009IMP, JH Formula 4, Keith Monks, Lustre GST-1 and at present a Grace 707 with a Denon 103. Record mat is the Hiraoka Diskmat SE22 I bought in 1977 at Harvey Sound (NYC, 48th Street) for $20! Still an amazingly fine sounding TT! The RD11 and RD11S are the Scottish cousins to the Linn Sondek. Actually, the progenitors! Ariston made the early LP12's before Ivor Tiefenbrun set up his own factory. He just copied the RD11 and marketed it as his own original design! Hamish Robertson was the owner/designer of Ariston who got HIS inspiration from the earlier - and wildly successful - Acoustic Research AR TT from 1961.

Gik 244 Panels and my Porter Port.  At one point, about 5 years ago, I sold off my entire set up yet still kept these, lol

I was going to say the speakers, but the reality is the Furman 15 A elite something something is definitely what has lasted the longest.

Silverline Sonatina speakers. Bought new in 2003.

I have Acoustat Spectra 33 electrostatic speakers.  I bought them new in 1988. 

Hales Revelation 3’s

We moved 10 yr ago, and I started over as far as most of the gear goes.

What I've owned the longest are some acoustic treatments (15 yr) and two JL Audio f112 subs (13 yr). Next is the equipment rack (9 yr), and after that the speakers (6 yr).

SOTA Sapphire.  Early 1980's.  Suitably upgraded over the Centuries.

Purchased in 78 or 79.  JBL 65. and McIntosh MA 6100 from Moe’s Sight and Sound, Casper, Wyoming.  MA 6100 being refurbished.

My amp acquired in 2004 it's a custom stereo tube amp from Deja Vu Audio in VA.

Ha! 1979! Probably still has that new component smell!

Mine’s a Pioneer TX-9100 Tuner, purchased new from the Tacoma Jafco with paper route money in 1974.

This however depends on the exact meaning of "in your system" since if you look at my system, which I encourage at all times and whenever possible, you will see way down low over on the right said Pioneer Tuner. https://systems.audiogon.com/systems/8367 No not the very bottom, that would be the Technics SL-1700 which is nowhere near as old, having been bought in 1976.

In any case while both of these are in my system room and in my system pics they are not at the moment actually connected. And so you being the OP and with of course having the hottest avatar I submit to you My Liege for this ruling.

If you rule against the Pioneer then that will of course apply to the Technics leaving the humble, vintage 1976 ZeroStat, burnished well with a patina of fine scratches yet still streaming ions like the day it was new.

Tandberg TD20A, since 1979.