After a long, long sleep: ML-335

The safest bet it to take it to an authorized service center.  Maybe there are some upgrades they can do as well.

All the best.

I am located in New Jersey if our location can be of service.

I'd say take a look inside like Eric said.  Power it up without it connected.  It and let it idle for 20 minutes.  If nothing seems burnging then plug that sucker in.

Happy Listening.

By any standard, your ML needs to be recapped. This is going to be expensive - at least $2K - but the amp shouldn't be used until it is serviced. I'm assuming that it has sentimental value and that you are going to run it in your system for some time. If that is the case then you are going to have to have it recapped. You may as well do it now before you risk any damage. If a board is destroyed the amp is likely to become a boat anchor. If it's like my Krell KSA 300S, replacement boards are rare or not available.

@ imhififan's comment is worth noting. It may not work to hook up a Variac to this amp because it may not trigger the power function with low voltage.

If you don't intend to keep it then I suggest that you sell it as is and don't turn it on. Explain the circumstances in your listing. This is a classic piece of gear and there will be buyers who will gladly take it off your hands in this condition. There are vey few amps available today that can double their power down to 2 ohms and they are extremely expensive. If someone is running vintage Wilsons, Thiels, Apogees, or other speakers with a brutal impedance curve, this amp was designed to drive them.

@bigkidz, @erik_squires...+1

I was a Levinson dealer and they use VERY high quality parts.  IMHO, you shouldn't have any problems, but use caution up front.

25+ years without power? Potential big trouble.

If it were mine, and I was short of cash, I’d pull the big caps and power them up one by one, very carefully with a variac, as @gs5556 suggested. And I’d put them inside a metal box beforehand - big caps can explode and throw caustic debris around. Then I’d let the cap under test sit, fully powered up, for a day. Then I’d turn off the power and see how long they kept their charge. Then re-install and power up carefully.

It doesn’t matter how good the quality is - an electrolytic cap is an electrolytic cap, and they do age. A sensible technician will power up his unused test equipment every month or two just for this reason. And some of that stuff, like my vintage Tektronix scopes, cost as much as a new Mercedes back in the day. That’s quality parts.

Or, you could just install new electrolytics. If it were mine and I had the cash, that’s what I would do.