Switching to solid state amp?

One could make a case to move from tubes to SS because they prefer the sound of a SS amp as that is a decision based on personal preference. One can also make a case that they don't want to pay for tube replacements. That is also valid with amps with expensive tubes (ie. 845's or 300b's) but if one is careful in choosing a tube amp they can buy one that doesn't use expensive tubes.

But to say one wants to go back to SS because they are easier to maintain or are more reliable is not valid. A point-to-point wired tube amp, with no printed circuit boards is one of the most straight forward designs to diagnose and repair.

I will look at the Octave it could be a good choice.  From what I have learned about the Diablo 120 the build and parts are quite equal to the Diablo 300 but the 300 is a brute.   I am sure the transformer is beefier but both have the same house sound.

I second the vote for and highly recommend Clayton Audio M300 or S2000.
You won’t miss tubes with Clayton, although I do keep a VAC Renaissance 5 preamp in front of the Clayton for even greater sound. All the best!

depending on your wattage requirements, klaus at odyssey audio builds amazing amps at great prices. i recently took delivery of a kismet and am just loving the sound. powerful, detailed, beautiful bloom - not overwhelming amounts. overall, love it more than my ayon spirit 3.

I agree with some comments above that matching your amp and preamp is still the most important factor and the only sure way about this is of course to listen to it.

Athough I obviously not tried all the combinaisons suggested above, my personal experience is pointing towards YBA with their classic series. YBA1, YBA2, and if you are ok with only 50W YBA3.

The company's founder Yves Bernard André brought two distinct technologies that make solid state sound very tubelike:
-) double C transformer that is exclusive to YBA. This transformer besides producing very low noise is also slow, that might look like a disadvantage but that slow reaction is a major part of making these amps soud very much tubelike.
-) he also got his own amplification class, the "alpha class" with is prety much a lower heat A class.  

In all the solid state amp I've tried YBA is the closes to tubes