fdd5d689_e_Notes_on_Coupling_Capacitors__Impressions_HV
[Brand] Reliable Capacitor MultiCap RTX (polystyrene) 0.47uF 400V tested $17.65 [Impressions LV] . [Rating] 4 [Impressions HV] 
I was warned against these by one of the vendors being told that they are clinical and cold which most people don't like. Now, he did say that about 1 in 100 people swear by them, but I also recall the words "solid" and "state" being thrown in there somewhere, and not in a good sense. I may be in that small group, but I find these to work pretty well. Like with the Vitamin Q above, these are not bloomy in the mids, which allows the mids to sound good on their own. Instead, they are very balanced from top to bottom, with maybe a small emphasis on the bass. Really good bass, good mids, and good treble without the PIO sparkle and just a touch of sweetness. Additionallly, the resolution is quite good. You might think of these as the little brother to a Teflon cap. They are not quite as resolving, but the tonal character is similar. Now, if you are running, and liking, resistor loaded 12AU7's, these are likely not for you. But, if you want to buy a cap that is balanced and has very little influence on the sound so you can get on with other things, these are a pretty good choice.
ecp audio diy: Some Notes on Coupling Capacitors
Impressions HV