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

There is no such thing as universally better parts—the right part is a matter of both particular design and taste of the listener.  That means trial and error and a willingness to accept that the majority of changes will be for the worse (the original builder having already chosen something that works reasonably well, your somewhat random change is likely to be positive).  It is not necessarily the case that parts that are popular will be to your liking.  
A custom builder I know passionately hates Mundorf caps and can tell when they are in amps and speakers just by there particular sonic signature.  Another builder I know was in some distress when the “cheap” Black Beauty volume pot was no longer made because they worked so well in his designs; cost was no object in his builds, yet he did not like some very expensive alternatives. 

Sometimes the right parts are very specific to the way the product is used.  A local dealer/builder upgraded one of his customer’s amps with Blackgate coupling caps. The customer had auditioned and liked the upgrade in the shop, but when he took his amps home the result was disappointing.  It took some effort for the dealer to determine that the owner tended to listen in short sessions while the dealer’s gear is on for many hours before the customer heard it.  It turned out the Blackgates needed the long warmup to sound its best in this particular amp.

Do you know what brand caps Mike uses? All the caps in my Quicksilver gear are labeled Quicksilver ( some made in France ). You might be spinnin’ your wheels changing out the caps. You should give Mike a call and ask him what brand he puts in his gear!
http://quicksilveraudio.com/accessories/

@larryi
I do appreciate your warnings and thanks for weighing in.

There is no such thing as universally better parts—the right part is a matter of both particular design and taste of the listener.

Didn’t mean to claim that.

That means trial and error and a willingness to accept that the majority of changes will be for the worse (the original builder having already chosen something that works reasonably well, your somewhat random change is likely to be positive). It is not necessarily the case that parts that are popular will be to your liking.

I totally agree. The idea that it would be *necessarily the case* that popular parts will be to my liking would be a very bad bet, indeed. It’s not the *popularity* of the parts, by itself, that makes it a good bet to try these changes. It’s the quality of the parts.

Sometimes the right parts are very specific to the way the product is used.

This makes sense to me. And yet the reason I’m likely to move ahead with this change is that
(a) while it’s possible that the fairly inexpensive caps in this amp are the "right" parts it seems plausible they’re there because it suits the design *and* also meets the economics of pricing and availability for these units;
(b) other QS owners of this gear report benefits from these changes;
(c) owners of other tube gear report benefits from their upgrades;
(d) it’s all reversible for not that much money.

If you were making great lasagna with great sauce (QS transformers, wiring), but with modest quality meat and pasta (some of the parts being considered for swap out, here) and someone suggested trying the same recipe with much better ingredients, it would be hard to resist taking things to the next level. It’s possible that the recipe completely relied on the modesty of some of the ingredients, but my guess is that better ingredients would improve things even further.

@yogiboy I have found the Orange drop caps online for less than $5. I would replace them with much better caps. The other strange value cap 27uF seems to be Solen.
@decooney has done the homework on these caps. I have not seen reports that they are special or from France or whatever, but perhaps there’s been variation over the years.

It looks like there are plenty of people who have upgraded to much better caps in Quicksilver amps. Couple finds:
  https://db.audioasylum.com/mhtml/m.html?forum=amp&n=156482&highlight=quicksilver+caps&se...

https://www.usaudiomart.com/details/649264974-quicksilver-tube-mini-monoblocks-with-latest-upgraded-...

besides the caps, you may want to also consider MILLS wire wound or Dale wire wound resistors for the plate and cathode values. Much more detail and better resolution due to the lower noise floor offered by the wire wounds over the metal film or worse yet, metal oxide. 

Greetings! I've used the Odams in two SETs, a PP amp and a two stage DC coupled preamp as the output coupling caps so far (I still have them in the preamp as an alternative "flavor" to compliment a couple of amplifiers). They all have over 500 hours on them. With the exception of the preamp, I found that they sound congested in the lower midrange and upper bass even after burn in, but are very nicely extended on both extremes. The Miflex can sound forward in some circuits, and I've found sound best when there is only one coupling cap in the circuit (otherwise the upper registers tend to sound vague and lack focus). I recently ordered a dozen Miflex KFPM, which are copper coil and metalized poly and have been burning in a pair. They remind me of the Audyn True Copper, but with much better detail and extension and the same midrange body and texture. They present incredible delineation throughout the range, albeit I'm getting a little brightness on the top end which I'm hoping will smooth out with burn in time. Jeff at Sonic craft recommended these to me, and they are one of his bang for the buck favorites. In the end, not all components will produce the same results with the same upgrades and the overall system voicing will dictate what sounds best. Look at it as a chef's spices, and you'll realize not every recipe tastes good with the same blend. Best regards, Aric