Tube Amp, Preamp upgrades -- what did you do that improved your units?

@grannyring Yes Solen Fast caps are made in France. They could very well be used by QS. They are the very definition of modest quality…at best. Dull and flat sounding compared to the better ones mentioned here. Used by many builders because they are very low cost. Some builders do have real cost constraints to contend with.

Yes, "modest quality" at best. A little "dull and flat" is a good way of describing it. The bottom line is the stock caps in the amps are built to a low price point. Well built amps and super affordable, yes. 95% of the regular customers are okay with the good sound and reliability in stock form. Makes good business sense for QS. The retail price is far below many others, and this is partly why.

The other 5% of us over the past two decades+ who’ve upgraded caps want to get even more out of the venerable QS monos. Upgrading with high-end well made caps (many mentioned on this thread) and better input/driver tubes allowed me to keep the amps, liking them now much more than originally anticipated. Amazing what these small and affordable changes did for the sound and added musical enjoyment. For added confidence, read through old and recent threads on AudioAsylum, DIYAudio, and other forums and you’ll find members who’ve completed these exact same upgrades on their QS amps with success. If you are going to do it, buy the best caps you can, it will likely pay off for you. Best of Luck.

excellent discussion and exchange of ideas from several experienced, well meaning, classy, knowledgeable folks

a pleasure to read and learn from

Very enjoyable, civil, and educative thread. Really appreciate your experience, your cautions, your calculations about benefits/detriments, and your descriptions of the many factors which make it hard to claim too much certainty about a lot of this.

I started this thread on the edge of a diving board, and now I feel confident to yell "Cannonball!"

I'll try to report back down the road.

Beware making changes in well designed gear.

I have seen both John Curl and David Berning deplore such 'improvements, saying that if they had wanted more expensive components in a given circuit they would have put them there - they designed for sound, not price.

And if you are talking about as market gear, I doubt that any substitution will make much improvement compared to buying a well designed piece of gear, even if it turns out to be pricy. (Sadly, there is lots of pricy gear that fails to give good sound too.....)

Had a few of coupling caps failed in a few tube amps, my current pre replaced all coupling and power supply caps with Vcaps, Mundorfs, and Jupiter.

Replaced IEC inlet with Furutec and went to Amperex tubes.

That said, things become more reliable but can change the sound for better or worse.