I recently got me this Yamaha CR-840 receiver for a 100 bucks. It's great, heavy, had only one owner and came with the original manual and the warranty card from 1979...when it was the-top-of-the-line model selling for 4-digit dollar amounts.
And of course one has to open up such a find immediately, before even testing it; I mean: look at the kardans from the selector knobs to the actual switches!
All the bulbs were dead or died on the first little bit of vibration (opening of the case) but that got taken care of next.
The original manual had the complete schematics (but printed in flyspeck-5), and I learned of the weird lighting setup: plop loads of 14V bulbs in a mix of series and parallel and they'll survive the 25V that the power supply feeds them. (Of course that means that a strategically failed bulb will also make a number of others go out. Silly idea, really.)
I had no easy source for 14V bulbs in the required format, getting fitting 12V ones took two trips to Jaycar already. And I had no high-wattage resistors around, either. Fix: soldered a number of .25W suckers together so that they don't burn up themselves yet at the same time do reduce the voltage for the bulbs' prolonged existence.
Finally I did the DC adjustments for both amplifier channels, and got them down easily to 0.1mV. Not bad for gear that old, and the sound is just great, even with my trashy loudspeakers. Beautiful, innit?