Well, my favorite CV378 variant is the Mullard GZ34/5AR4. RCA relabeled the mullards back in teh 60's. It's by far the smoothest I've found. These things come at one heck of a price though. I've seen $90 on ePay. Kevin at Upscale might cut you a deal, maybe.
The Sovteks and Svetlanas will work in a pinch but they are pretty hard sounding, especially in horns.
After the Mullard there are two that sound almost as smooth. The first is the Raytheon 5U4GB. It has the twin top (side) getters. The base is the black plastic. The next one is the Hewlett Packard 5R4GYA, brown base. Both of these have fairly nice sound. I haven't tried to find these on eBay but I've not heard many people talk about them so they may be a sleeper.
If all else fails, try this.... Get yourself the Sovtek 5U4G in the ST bottle. Drop them in your deep freeze until Friday night (assuming you have a deep freeze rather than just the freezer on teh side of your fridge). leave them in there until late Friday night then take them out and let them thaw until morning and they'll be ready to use.
This is essentially the 'poor mans cyro'. Granted, 0 deg F is no where near -380 (or what ever it is) of liquid nitrogen but what you are doing is providing (some) stress relief to the plates and filament wires. It would be best if you had a full week if not two to do this.
I know some of the guys here poo-poo'ed an errant poster about this a while back but it works. I've known about it for several years in fact I just this week popped a pair of Chinese 300Bs out of the deep freeze for my DRDs. Before they went in, they were a bit hard and etched sounding. Now, they have smoothed out quite a bit. They still have the same amount of detail, nice smooth highs, etc but that course sound is now gone. I did some driver tubes too but I haven't popped them in yet.
If you don't have a deep freeze, get a cooler and some dry ice, that works too. Just be sure add more ice every couple of days.
