some 70's and 80's receivers seem to be popular

I just finished rejuvenating my Marantz 2230, which resides in my basement system. 73 new electrolytic caps, 8 polypropylene film caps to replace old mylars, new lamps, transistors cleaned and re-seated with new micas, etc. Total cost was $20 for the receiver and about $70 more for parts. Teamed up with some speakers from about the same era (I've rotated in EPI, Rogers, Mission, Advent, and Dahlquist - I have a lot of old speakers) , it sounds FANTASTIC.

Be careful about changing parts...

I'd be careful about changing out capacitors and other parts - if they have failed then you have no choice; but you might find that changing an original part for a new equivalently spec'd part changes the sound. I think many parts were chosen (in the good old days) not only based on specifications but they were also "voiced" (ie, listend to) - specs alone don't tell you everythying about sonic characteristics. Much of the magic of the vintage gear being discussed here is that these units were designed and manufactured by firms that had a passion for what they built - and that included listening to the gear and not just measuring specs.

Well, I don't know if it was my 16-year-old ears or what, but I spent endless hours in the 70's parked in front of my AR Receiver (AR turntable, Shure V15 type 2 cart., Dynaco A25 speakers) in total bliss.
I must have listened to the White Album or Tapestry or Steppenwolf Gold or Blood Sweat + Tears a hundred times each.
Of course, I guess I should have gotten out more to get a life...