Should I replace my 20-year-old Hovland Radia Amp?

The problem usually with age of capacitors. Like it or not, 20 years is a long time for a typical cap. So you may either recap the amp or get a new one.

When I got the amp one channel went out after about six hours. I took it to a high-end audio technician. He charged me $800 dollars and said he'd replaced the bad parts. I hate to say that I know little about electronics. I really don't know the difference between a resistor and a capacitor. And I have no idea what he replaced. Perhaps he recapped the amp? It sounds very good to my ear. If he did recap it, would there be anything different in terms of electronics between a new Macintosh amp for example and the Hovland which apparently was made with the best parts available twenty years ago?

Power output:

125Wpc into 8 ohms 

200Wpc into 4 ohms

So this is what you're talking about, got it.  I gotta say, it's an attractive piece when it comes to industrial design.  Stating the obvious, a Hovland preamp back in the day would be logical.  I happen to have a late production HP-100 in my stash; I love that preamp.  It is very musical.  Anyways...

I noticed you have an excellent 3-box preamp in a Pass Labs XP-30.  I had the predecessor, the 3-box X0.2 model.  This next thing is important, when I paired that to my Pass Aleph 1.2 (single ended class A, 200 wpc into 8 ohms), it was pure magic. I thought that was a mediocre amp until the Pass Pre landed in my rack.  Then, once the amp was on for about 45 minutes - bam!  It would catch it's second wind, sprint off and that wonderful glow and lit from within musicality along with that glorious midrange would just rope you in and command your attention.  It was a jaw dropping moment for me because I had tried 2 or 3 other pre's and was about to give up on that Aleph 1.2.  

You must, I repeat you must buy a Pass amp, preferably in the XA-xxx.5 or the XA-xxx.8 and mate that to your Pass XP-30 preamp.  The current generation of Class A amps is the ".8" series.  I listened to both the XA-200.5 and the XA-200.8 monos.  I bought the ".5" mono amps.  Perhaps being $20K less expensive has something to do with my choice but to my nit picky ear, there is something about the ".5's" warmth and liquid midrange that just snags my attention.  It is hard to explain, it has this wholesome-ness and I guess that certain inner glow that the .8 does not muster-up as well.  Okay, the .8 though, in short, it is the better amp holistically.  The greater air and separation plus captivating pin point position of singers and instruments emanating from a black 3D space is pretty satisfying though.  The .5 does not lack in bass, but the .8 is better in that deep bass that anchors music down and gives it that certain foundation.  

As usual, too wordy.  Sorry.  In less words man, you must try a Pass Class A amp.  The symmetry of having that Pass preamp+amp combo, ya have to hear it to believe it.  You'll also be floored how black the negative 3D space is, and when the singing starts and instruments come in, it is something else.  There, I said it.  At least try a Pass Class A amps; you'll be glad ya did.  Lastly, Pass gear cold is good, but Pass gear when it's roasty-toasty hot, it is something to behold.  Have a prosperous & Happy New Year!  

Simple answer, yes, I would give something new a try if you are curious. Pass or Coda would be good candidates. 

My 2 cents, if they're worth that much since I have no personal experience with any of the components involved:

The Sonus Fabers have three 12" woofers on each side and an impedance curve that dips below 3 ohms in the treble range.

The Hovland amp pushes 125wpc at 8 ohms and a modest 200wpc at 4 ohms.

On paper at least, it seems reasonable to wonder whether the Hovland can provide enough current to meet the Sonus Fabers' needs / preferences. They wouldn't be the first big speakers that sound fine in front of 75wpc tube amps, but only come alive when mated with high-current amps that maintain their composure below 2 ohms.