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

I upgraded my input tubes on the phone and amp. The phono got a NOS Telefunken 12AX7 and the amp got 2 x 6922 NOS Siemens. Huge increase in soundstage and much more air around each instrument. Highs are crisp and clear, not sibilant. YMMV of course.

Tubes are, i had thought, already a given. I’m thinking of alterations to the machine.

Also, learned this: the Orange Drop caps are 90 cents (.90) a piece at Tube Depot. 
https://tubedepot.com/products/orange-drop-715-series-022f-600v?utm_source=google&utm_medium=cpc&adpos=&scid=scplpCP-OD715-022-600V&sc_intid=CP-OD715-022-600V&gclid=EAIaIQobChMIsIa6_8yH9AIVeQytBh0nbQ4EEAQYBCABEgICr_D_BwE

some of us remember swapping in Orange drops into a Hafler…because they were an…upgrade… it’s all relative….

I would do what I said above with your preamp.  Replace the Alps Blue pot with the same value TKD. The potentiometer has a sticker on the back that tells you if it’s 25k, 50k, 100k etc…. Nice step up in resolution and realism. More than replacing a cap. This can be found at Parts Connextion or Hifi Collective. I think the TKD pot costs just under $100 shipped. 
Replace those white caps labeled QS behind the tubes, 2 of them, with Vcap Odam 2.2 uf.  600v. If too pricey for you use the Audience XO caps. The Odams are wonderful in every way and a nice step above the Audience. The Odam caps will cost around $100 each.  The Audience caps about 1/4 that.  
You could replace the 4 - 47uf 500v filter caps with Mundorf M-Lytic HV 500V 2-Lead Single Section Axial cap from Parts Connextion.  If the amp is 10 years or older, then consider this upgrade.  They cost some $11 each. 

@grannyring Thank you. This is all for the preamp. One thing -- the amp is not that old -- it was probably built in 2020 or 2019. Would you still replace those 4 - 47uf 500v filter caps? It sounds like you'd only do it if it was an older model. Thoughts?

Also, did I miss your thoughts on the mono block amps? 

@tomic601 I suppose it’s all relative. My amp is a 2020 model so I’m not sure how those orange drops stack up, relatively, *today.*