tube pre amp and Krell FPB 600

I agree that it is not likely a preamp turn-on or turn-off thump will damage the power amp. The real point is the damage to the speakers. Krell has good reason to be concerned about this in my opinion.

Since I have been all-tubes for many years, including phono, linestage, power amps and even DAC, I really don't have a dog in this hunt. Whatever Krell does or does not do is of no concern to me.

I would never underestimate, however, the ability of some well-meaning audiophiles to mess things up. I clearly recall a lengthy exchange I had on some forum, probably Audiogon but I am not certain, where the other party was insistent that a preamp should always be turned on after the power amp, never before. (That is not a typo.) He dismissed my concerns about possible damage by saying he had never had a problem or experienced any thump for 20 or more years. Of course, his good experience hardly proves the rule; it just shows the muting relay in his preamp works.

CT0517, I do have the owner's manual, I have read exactly what you have specified many times, it is a whole page, I do not believe it would hurt nothing to do the power up and power down scheme that Salectric has told me, I never thought of it, makes sence to me,I'm going to do it, The tube/solid state digital source I use straight to my amp in no way could spike anything following Salectric's advice, I have always used all solid state, likly that may be the reason I never thought of doing a procedure for on power and off power of Tubes mixed with sold state audio equipment.

^^Even if you have solid state you can get a thump. The reason you don't is your preamp has an automatic mute.

Many tube preamps do nowadays too.

I always get a thump sound over the speakers when I turn my amp off, it's really alot of power, seems normal to me.

I've had 3 Krell amps over 10+ years and always drove them with tube preamps (SF, McIntosh, CJ ...) and never had a problem.

There are reasons for rules. If not followed, probability of problems increases.