Coupling caps

Although late to reply on this older post. Frankly, I never heard better capacitors than the Russian K40Y-9. It is the most musical capacitor I ever heard. Needs 50 hours to start sounding right & first 10 hours is not so good at all.

A killer combination Jupiter Copper foil Bees wax cap
And 30% Arizona  Blue paper Mylar oil capacitor 
Very close in some way better then  Duelund Cast capacitors.
Jupiter condenser  carries both. If you have yo use a Big value 
Say 30uf  then buy the new Clarity Csa-  cap,  20uf ,                       5uf Jupiter Copper 5uf, and 5uf the Arizona Cactus Blue  capacitor
The Blue has the best bass of the 3, paper and Mylar mixed in,more Mylar for depth.  cactus caps red is all oil paper very nice for mids,highs .newer green has more paper yo Mylar ratio in oil 
Good Bass just not quite as fat sounding.  Original company-
West cap made msny of the vintage guitars of the 60s sound 
That classic great sustain  and warmth .in your sudio fantastic 
The new designs 3 Very hood engineers from Japen took  on
The challenge and did a great job  .red caps small values.

Just call them and give them the value you want. Make sure you know the uf value and voltage rating. I purchased .47 uf at 600v.

They require you to call in. That is what I did.

Thanks for the response. I can't locate these caps on the Arizona Capacitor website. Do you have a more specific product number?

Jarrett, I am a confirmed cap roller and have checked myself into a 12 step program to break the habit! Based on what you are saying, and I share your sensitivities to upper mids and highs, your best choices would be....

1) Arizona Capacitor Green Cactus caps - best choice and $25 each
2) Jensen paper tube PIO and Jupiter copper foil or aluminum flat stacked

I have rolled in SET amps like yours and these caps will indeed please you greatly.