Capacitors drying out in an old amp

Depends on the amp and build quality. My McIntosh MC225 is all original and has no problems. It was built in the mid 60s, making it 40 years old.

It has little to do with the build quality. A 40 year old electrolytic capacitor is not behaving the same as a new one. A 40 year old amp may be functioning with no apparent problems, but it is not functioning as well as it was when it was new.

Well, my MC240 was recapped due to a slight hum and the sound quality is now perfect....like the MC225.
GO FIGURE!!

Hpims, thanks for colaborating my point with your experience with the 240.

Electrolytics deteriorate and must be replaced periodicaly. If the 225 starts to hum tomorrow do you think it was perfect today. NO, the sound degrades slowly and at some point the cap will deteriorate to the point that you can hear some hum, but the sound has been degrading long before you hear a hum.

Quado, in 1999 I replaced the Mallory brand, computer grade, large can electrolytic caps in a circa 1985 Threshold S/300 Series II. I stuck with the same brand and capacitance value although many prefer to enhance it. The change was easy and required only a screw driver and attention to their orientation. Sonically, the new caps may have imparted some smoothness but the real difference was slight if any. The main benefit was not worrying about it anymore. Although these big caps begin to degrade the day they're made it doesn't mean the sky is falling. Replace yours before they hit 20 years and you'll be OK fine.

On my amp, self adjusting has to do with regulating the bias of the output devices, which sets the amount of current flowing through them continuously as opposed to having them switch completely on and off.