I will back the Classic 60 Amp also.
Have owned mine since New, and it has been Rebuilt and Modified by Scott Frankland and Associates. He installed Bias Pots on the Back Deck & Test Probe Ports on the Side in proximity to the Bias Pots. Absolutely brilliant since all I need is my milli amp Tester (Voltmeter) with Probes and Adjust, and or Check the Bias Monthly.
Scott has also Replaced all Caps and the Amp works flawlessly.
In the time that I have owned this Amp since New, I had one Failure a number of Years ago when I tried KT90 Tubes. One Tube blew the Grid Resistor and it also took out a FET.
Recommended Tube now, even by Audio Research, is the Sovtek 6550WE which is the only type that I use. KT90 Tube experience was not pleasant.
Months ago, I started researching:" What Amp would I replace the Classic 60 with if needed? " After many Months' reading everything I can get my hands on which includes this Forum, I do not have a Clue.