Here' s a good place to start:
http://www.krellonline.com/history.html
Pesonaly I'm not a fan of of amps with fans, so the earliest Krells don't work for me. The KSA 80/KMA 160 and KSA 200/KMA 400 series are amongst my favorites. Caveat, these amps are now getting old and might need new caps, re-biasing, etc.. It's been reported here that Krell's charges for these services can be quite expensive. While the true audio Krells (IMHO, that doesn't include their intergrateds and AV stuff) have a common signiture, there are notable differences between different series. Good luck.
http://www.krellonline.com/history.html
Pesonaly I'm not a fan of of amps with fans, so the earliest Krells don't work for me. The KSA 80/KMA 160 and KSA 200/KMA 400 series are amongst my favorites. Caveat, these amps are now getting old and might need new caps, re-biasing, etc.. It's been reported here that Krell's charges for these services can be quite expensive. While the true audio Krells (IMHO, that doesn't include their intergrateds and AV stuff) have a common signiture, there are notable differences between different series. Good luck.