The Sunn Beta amps are full of low Voltage electrolytic capacitors. These caps have a service life of 10 or 20 years depending on how often they were used and under what conditions the amp was stored. They actually last longer if the amp is turned on once a month or so. They can degrade slowly, or fail suddenly when the amp is turned on after a long period of storage.
Since these caps are used in many parts of the amp, they can cause a wide range of problems when they fail. If you replace just the one that is causing today's problem, you could have a totally different problem next week because a different part has failed. The only solution is to replace all of them. This won't be cheap because of the significant amount of labor involved. Because the labor is much more expensive than the parts, premium high temperature long life parts should be used. In some cases, a stacked film cap should be substituted for the electrolytic cap. They last much longer.
The amps made today are much the same way, but they are so cheap people just throw them away rather than fix them. If some amps fail under warranty, the company just gives you a new amp rather than fix the broken one. And if some computer chip fails on a modeling amp, you probably won't be able to get the parts to fix it at any price.
