As Dswankey said from the current pics, no way to tell. You'd need to remove the amp, flip it over and remove the bottom panel and take a few pics. Same with the 400-CX2. FISHER Tuners don't need much and are generally in good shape, although I'd have them check it also.
As you've already checked it out operationally (turned on and checked operation), there are some operational checks you can do while it's on.
1.) Find one of the guys with a tube checker in the area and test all the tubes. replace any weak or bad tubes. Weak tubes will still work, but you won't get all they are capable of.
1a.) Take a 1" DRY PAINT BRUSH and brush off all dust. Use a vacuum cleaner also. Try not to use SWMBO's ORECK, or other vacuums she uses in the house. If you have no other choice, get permission 1st. And then change the bag afterwards. (stay on her good side!
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2.) let it run for a 1/2 hour or so to let it warm up and stabilize. touch the CAN CAP's and check the temps. They will be warm due to radiant heat from tubes and transformers surrounding them. But they should NOT be warmer than that. If one is, TURN IT OFF, UNPLUG IT and Mark it with a sharpie. Write a down check note on it.
3.) If everything is ok above, go ahead and run it, and stay in the room. If it starts to act up, SHUT IT DOWN NOW! Unplug, and write up a down check note on it. Otherwise run it but stay in the room with it, check the temps of the can caps occasionally. You want to be close enough to turn it off fast. It might be better to connect it to a power strip so you only have to throw one switch.