Since the amp hasn't been used in 30 years, I would say that you should replace all of the electrolytic caps in the amp before you fire it up. They would most likely be worn out anyway, but having not been used, they are sure to be worn out. Since there are high voltages in that amp, you should get the exact replacement can cap from Triode Electronics (I think they are the ones who stock that one), or you would have to use series connected caps inside the chassis to get a high enough voltage rating. I rebuilt one of those recently, and made some mods to it also. It is now a great gigging amp and sounds VERY nice. The Sunn stuff isn't bringing high dollar yet on the used market, if it ever will. They are very well built and good soounding amps however, and so often have more value as a player if you can get them cheap enough.
I got mine for $40 off ebay and it had some problems. I spent a couple weeks wiring up a true ground buss and ground lift switch, replacing all the components in the amp, and then tweaking the filter caps to get a better bass response. I ended up with 110uf in the first cap stage, and 50uf in the second, and a 300uf cap on the cathode of the first preamp stage in the amp. I also have a 2000S that is bone stock, and the 200S now sounds better than the 2000S for bass, and it also hums a lot less because of the grounding mods I did. If you know what you're doing, I would probably repair/mod the amp yourself and keep it/use it for gigs.
