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

@grannyring Yes on the .27uf combo from Audience or Sonicap. Both should be a step up. I am basing this on the parts quality used throughout the amp which are modest. Someone is making the QS caps, but I am fairly certain they are not quite up to the Audience XO level of quality. 
Yes on the 47uf preamp caps. I added the bypass idea which is a no brainer and will yield sonic improvement. Look up the dimensions of this Mundorf cap and be sure they will fit. Just make sure. I bet they do, but……

Yes, agree. Modest at best on the stock caps in the amps and preamp. Studying a bit inside, maybe Solen or Sonicap ? is OEM with the odd .27uf on the amp IT side and 2.0uf in the preamp. The mfg owner-designer shared he likes aluminum foil caps. There are four $4 715P Orange Drops in these amps on the OT side. Replaced those on mine after year one, along with a five+ others who followed here on A'gon. Yep, a no-brainer.  I was astonished at the results, making the simple cap upgrades for these very solid amps which already have good bones. 

grannyring has good advice above.  I like the VCap Odams much.  They are also easy to work with size wise. But you'll need to tell your tech that their bodies are somewhat conductive. I wrap them in silicone tape prior to install.    I would simply start with the coupling caps and output caps (typically located right before the lines running to RCA outputs).   If it's a preamp you are upgrading, you can match your output cap better to your amp if they are of different brands.  There's a nice calculator on the VCap website for this purpose. 

I was never able to find a tech that wanted to assist with modifications.  It's kind of like taking your car to a service place and asking them to install specialty muffler, brakes, etc.  They typically aren't jazzed to do it and they look at the vehicle as if it were an appliance--not to be touched from the engineer's design. 

I've experienced far more meaningful results upgrading caps/resistors than I have playing with hookup cables/power cords (I do that too but I just hear more of an improvement from the other stuff).  

One warning you didn't get yet---It's slightly addictive.  I spent $900 upgrading my crossovers on my loudspeakers.  I bought Cornwall IVs but would have loved Volti speakers (didn't want to spend $10k).  The crossover upgrade got me where I wanted to be.  

Modifications can keep me from upgrading by allowing me to get more out of a design I already love.  A Ford Mustang or even Chevrolet Corvette are built to a price point--they are not a Rolls Royce. So there's a good foundation to make improvements to your specialized taste.  Enjoy your journey!

@jbhiller

I would simply start with the coupling caps and output caps (typically located right before the lines running to RCA outputs). If it’s a preamp you are upgrading, you can match your output cap better to your amp if they are of different brands. There’s a nice calculator on the VCap website for this purpose.

Thanks for weighing in. Help me understand -- you say the "output caps" are "typically located right before the lines running to RCA outputs." My amp only has RCA inputs. I’m looking at a picture of the inside (at my system page, hilde45 ) and I’m trying to determine which caps you mean.

As for the preamp caps, I AM intending to modify BOTH the preamp and the amp. Your advice helps me because I’m leaning toward Mundorf for the amp and then could do VCAPs on the preamp.

I would not use Mundorf film caps for your amps. They are rather tipped up in the upper midrange and can sound a tad too brilliant and artificial. This is compared to the better sounding caps like Vcap Odam, Jupiter copper foil, Jupiter HT and others. These other caps are more coherent top to bottom. I am referring to the Supreme silver/oil and silver/gold/oil caps. I am not referring to their line of electrolytic capacitors.
My experience after using them several years ago.
If you are looking for some tipped up energy in the brilliance area, then the Mundorfs may be a good choice.

The  film caps I pointed earlier are all coupling David. The 2.0 uf white caps in your preamp are output caps sometimes called output coupling. You can use the Odam 2.2 uf there. In this output position 2.2uf is perfectly fine. This position is not the same as the stage coupling caps we discussed not changing the value of.

Re: Mundorf EVO Silver-Gold (non-oil) version sku #80510 is smoother, .22uF 1000vdc, and is not "tipped up". Actually,  the non-oiler version caps are better sounding than the Silver Gold Oil (SGO) version with oil in amps.  Yes, the opposite of what most might think about adding "oil". I learned this from an amp designer colleague when using them in my larger Cary amps, Cary preamps, and now using them again in my Quicksilver Mono 120s with KT150 tubes. 

>>They DO sound more pronounced until fully settled in. Easy to get impatient<<

Kinda discovered this by accident after not wanting "oil" caps that dry out in my prior big amps that get hot. 200hr burn-in required on the non-oiler version cap too, and it is an aggravating roller coaster ride before the EVO silver-gold non oil caps truly form and stabilize to their final set point. Sounds nice when they do.