Turning off tube preamp first sends solid state amp into protection?


I have been experimenting with using a vintage Luxman CL40 valve preamp as a separate preamp stage for my L-509X integrated. Because I leave the solid state amp on 24/7, I accidentally turned off the preamp while the 509X was still in Separate mode. The integrated immediately went into protection mode with the power light blinking. I powered it down into standby mode, then brought it back up and it remained in protection mode. It wasn't until I unplugged the 509X and plugged it back in that everything was cool. 

Did I do any potential damage here? What it it happens again? It's pretty easy to accidentally turn off the preamp when I'm leaving the 509X on all the time.
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harrylavo, thank you. I wouldn't call myself a 'green' person but I am not wasteful. If the power consumption is low (manual says 150W...which means nothing to me) I'll certainly leave it on standby. Plus, the power button is tiny and out of the way. The 'standby' button is huge.
If you have separates the rule is always turn the amp off first, not the preamp.  Otherwise you can easily get the same problem, be it solid state, or tube.  It makes no difference. Shutting off the preamp while the amp is on sends a spike to the amp.  Depending upon the amp's design, it may shut down, or make a scary loud pop sound.  My NuForce amp and preamp used to give me a scare once in a while.  That is when I learned to stay with a "soft off" that left the preamp in standby.

Does it matter though, if all components in the chain have mute functions ? I’ve always been curious about this. Out of habit I always follow the above mentioned sequencing, and also leave everything muted during the process, but wonder if it really matters, as long as I un-mute (or mute) in correct sequence. Any thoughts ?

Don’t be lazy.

The rule is quite simple: preamp on first, amplifier on last. Reverse for off.

Its easy. Really. It is.
Guy walks in to his doctor's office and says "Doctor it hurts when I do this." Doctor says "don't do that."  Henny Youngman