Upgrading Quicksilver preamp or amp caps -- warranty impact?

+1 what @johnss said. If you are going to do it, don’t skimp, buy very high quality caps. Leave the work to a competent professional, and don’t forget to discharge the caps if you do it yourself, proceed with caution.

While people do it hoping to make improvements, as I recall the man himself founder/owner/designer prefers people not mess with his amps (at all), and to keep it under warranty. Makes sense, I’d say the same if I had to warranty my products and did not want people screwing around with my designs. Definitely the safe way to go. Or, buy his caps and what he likes. And, then you have the DIYers who want something more and different.

In my case, wanted to test the exact same caps I used in my prior Cary amps, to see how much of the sound was attributed to the circuit designs and tubes, and how much would actually carry over with cap change alone. After using them in a few other amps, Installed the exact same SilverGold caps used in TOTL Cary FE211 Founders Edition Mono amps, now installed in my Quicksilver Mono 120s. A lot carried over, surprisingly. Would not have believed it myself unless I had tried it first hand.

Removed the factory installed affordable and reliable $5.95 Orange Drop caps (used a lot in guitars) originally insatalled in my Mono 120 amps and replaced them with $50ea (2 per amp) Mundorf Capacitor 0.22uF 1000Vdc MCap® Supreme EVO SilverGold Black SESG (non-oil) version. Same microfarad, and higher voltage capacity.

Piano keys now sounds like piano. Guitars sound like guitars. Tone, texture, delicacy, transparency, depth in my former amps is back again. Warning: the super long burn-in roller coaster ride can be very frustrating with some of these high end silver-gold caps for first 0-200hrs. Worth every penny and the wait in my particular situation, never looked back, YMMV.

@decooney 

Removed the factory installed affordable and reliable $5.95 Orange Drop caps (used a lot in guitars) originally insatalled in my Mono 120 amps and replaced them with $50ea (2 per amp) Mundorf Capacitor 0.22uF 1000Vdc MCap® Supreme EVO SilverGold Black SESG (non-oil) version. Same microfarad, and higher voltage capacity.

This makes a lot of sense. Is it possible that QS uses a $5.95 cap because it's the best one for the design? It's possible but not probable. He's making an amp to a price point. The tubes in my QS preamp were $12 each. Replacing them made a big difference.

Paul McGowan discusses this issue in (at least) two videos.

https://youtu.be/bq5Ph2ySlD8
https://youtu.be/mpqUsEAk39g

If I were a mainstream mfg, I too would likely focus on Reliability, Availability, and Cost to stay in business. All key factors. As long as the "standard" version lasts and sounds "good enough" for 95% of the mainstream consumers, it keeps variation away, keeps costs down, and makes the product more affordable for consumers. Makes good business sense. Let the other 5% of DIY’ers do what they want to do and take on the risk themselves, etc etc. Less headaches for the manufacturer. It also comes down to those who want upgraded vs. standard. Standard works fine. And, sometimes changes or upgrades don’t always work better, fwiw.

as mentioned, the manufacturers can not afford to install high end copper foil caps, they retail price increase would just be too much. Also if you want to go further, replace the bias and plate load resistors with wire wound. will make the amp much quieter, and let more micro detail come through. But again, not cheap.

@hilde45 I have reached out to Mike recently about using lower gain tubes and have not as yet heard back. 
Let us know if you do. 
P.S. I may be putting my current version of his Line Stage Preamp up for sale soon as it’s not a good fit for my system.