Capacitors drying out in an old amp

If one is evaluating old amplifiers how does one know if the capacitors are drying out/dried out. Does the drying out process take a long time? Say, 1 or 2 years or is it quick?

Can the ears tell us if it is so?

I tried to check this but could not come up with anything. However most agree that an amp which is over 15 years old most probably needs the capacitors to be changed.

Quad amps have the current dumping system and according to what I have read are sort of self adjusting amps which do not change the sound characteristics over certain period of time. Is this also related to the issue raised above.

Sorry for so many questions but if someone can explain in laymans terms if possible, it would be greatly appreciated.

The only ones that deteriorate are the electrolytics.

Check out this discussion of aging capacitors. If it were mine I would change them. It is cheap and easy if you can solder.

The current dumping topology is another matter.
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 the MC225.
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.
Wazzup All!

I'm reading this with great interest. I have a 15 yr. old Dolan PM-1 pre-amp and was wondering whether the internal parts have deteriorated over the years. The Pre-amp hasn't been used for the past few years and is just sitting in a closet. I'm currently using a Music Reference RM5 Mk III pre along with a MR RM9, both tube components. I've been contemplating switching out the pre-amps just to see (hear) what'll happen. Is the deterioration being refered to in this thread due to heat output? Any thoughts would be much appreciated, thanks!
Thanks for the responses guys, I am learning!

Let me clarify as to why I had posted the message asking about the capacitors drying out. Last weekend I was trying out a few amps which were old and although they all sounded different, some were not sounding satisfactory. All those amps were between 10 and 20 years old.

I spent the entire Sunday hooking them up and after conditioning of say about an hour or so, did some critical listening. One of the amps was a real disappointment and that was a Marantz PM-94 140 watts/ch quarter of which was Class A (1988) . This amp has garnered cult following having a dedicated website and some consider it to be the best from Marantz. I was very curious to find out what the sound quality was like since I had owned one of the Marantz amps (PM-80) in the early 90’s which also offered 25 watts in Class A mode. This amp was nowhere sounding as good as it should on the bases of what I had read about it and my memory of the one I owned. The bass was loose and sounding boomy, the overall presentation was nothing to write home about. I thought that this performance just cannot be and there has to be an explanation as to why it sounded so mediocre This actually made me think about the capacitor problem having read here on A’gon as well as other sites, hence this thread.