How will I know when a Krell KSA-80b needs to be recapped?


How will I know when a Krell KSA-80b needs to be recapped?
cocopah
I don't know from personal experience, but I visited a quite reputable hi-fi repair shop in Nashville, TN and they said don't ever recap until they are physically leaking.  

Recently bought a 20 year old krell KAV500, worked fine for couple weeks, now I hear popping sounds from the amp while it's on and even after it's been off for several hours. It works well otherwise, full power to all 5 channels. Sound lasts less than a second and I hear them about once an hour. I was told the unit was recapped priror to purchase. Is this a cause for concern ? 
A technician and/or factory trained person will bench test the unit
and check to see if the unit falls with in the factory spec.  If it fails to reach the numbers, then recapping and replacement diodes... etc will be called for.  
All companies will bench test wether it's off the assembly line or
in for an upgrade.  This is just standard quality control.  If your Krells
sound fine to you then why spend the money on new caps that will have
to go through the break in period?
(thats if you can still get the same components)
The hotter an amp runs the faster the caps will deteriorate. If you have owned it since new you can guess how many hours are on it. If not things like heat-sinks turning from black to purple or even lighter would show lots of hot hours. A tech can look at the ripple on the caps and see approximately what shape they are in. Personally I would not like caps leaking in my classic Krell ever. I would have it looked at if you are unsure of condition.

Don S
I had this done on my KSA 80B in 2018 at the Krell Factory.  The did recap the PS with the big caps, and also several caps on each board, and set the unit up to drive one ohm Apogee Scintillas.  Been running fine ever since--3 years now.