Best caps for updating my VTL 225 mono's ?

For coupling caps the v-caps are hard to beat. If you want the best sound, get the Copper V-caps, they are so organic. They do transform the sound of a system. The improvement is not subtle. I hear greater improvements with caps than power cords, interconnects or bolt on upgrades. They are all important, but this one is big. . Look at the review in the Great Capacitor shootout, and in the Chinese hifi journal on the V-cap website. The downside is size, they are big, and expensive. In that quantity, you can get a better deal. If you don't want V-caps, the REL RT polystyrene are great and the Theta RT are also very good. They are not V-caps, but closer than some of the others listed. I would avoid oils as most of the people I know who used them in coupling positions got to clean an oil slick out of their amp....no thanks,....many oil caps don't like heat. They are fabulous in speakers as a Xover cap though. Mundorf Silver/Oil are legendary.
If you got the money, get the V-caps if they fit. Otherwise, the Thetas are great (Parts Express) or the REL RT's, a very sweet cap. The Dynamicap is also a good choice. If you can, get 600V if they fit.
Best of luck, and use Cardas silver/lead solder. I am green, but lead is so much easier to work with.......

Thanks so much to all of your responses. Any experience with or knowledge of Clarity MR caps in tube amp applications?
Thanks again!

Marty, as always, beat me to the punch. When it comes to value for money, go with the surplus Russian military PIO caps.

I first found out about these several years ago from my buddy, who happens to be that anonymous author of the widely quoted Capacitor Shootout. Though the overall grade he awarded them was low, and thus there hasn't been the feeding frenzy on them there would have otherwise been, a careful read shows he found them to be in the top three in some respects. Suffice it to say he's a big enough fan to use them in his own gear; almost exclusively, in fact.

I was recently talking about them with a coworker of mine who emigrated here from the Soviet Union. And, like most of his ilk, he's an audiophile, though not to the silly extremes we go to. According to him, they find it difficult to believe the "high" prices we're willing to pay for them. Until recently, when some there realized they could make a few bucks selling them to us, they literally were thought of as trash, mountains of it. However, he did maintain their build quality to be far in excess of anything that these boutique high-end audio companies could ever dream of.

As mentioned by Jallen, be careful with PIO caps in a hot tube amp chassis. Most PIOs are rated to 65C(and some optimistically so), as compared to 85C or above for dry constructions. ClarityCap MR has a dry construction and is treated with encapsulation and several other techniques that reduce microphonics for the effect of smoothness & relaxation similar to oil, but without the blurring that typically accompanies oil. The main problem has been unavailability of MR in the .1uf-.68uf range applicable to most tube applications. These small values are now available on an OEM basis and may be forthcoming through the retail channel.

Personally I'm not a big fan of Russian K40Y9 for signal coupling, but I like Russian SSG silver mica for small bypass applications. IMO these are more refined in treble than the Russian FT teflon series. If you can get by with 350Vdc, you might try paralleling a .01uf/350V SSG with your chosen .47uf base cap. The mil spec russians are typically conservatively rated for voltage so you should likely be fine.

Dave
ClarityCap North American OEM Sales Agency