Which tubes? My amp can except El34, 6L6, KT88, an

Sort of like asking which flavor of ice cream you should choose? They are all good but different. I am a fan of 6550's and EL34's out of the four you mentioned. I would think that you won't get the power from the EL's that you will from the 6550's or if you do they can't last very long. I have Vandersteen's(not 5's)and run a 6550 based amp which is a great match. I would start there and use them as a baseline or benchmark to judge from. You may end up eventually running one of the others, but good Svetlana 6550c's can be had for about 1/2 the price of decent KT88's so if you don't like them you don't have as much into them.You may be able to talk with your dealer or with Quicksilver and tell them some of your preferences and they may be able to make a rome qualified recomendation. I am going by the idea that if you like the same speakers I do you may like the same tubes.What is in the amps now? I'll take coffee ice cream, thanks.

Creeper and Kana, I have no problem with what you say about the sound of the 6L6, but you need to know how the powered woofers work in the Vandy 5's. The woofer amps take a speaker level signal from the main amp. They are designed this way to blend and have the same nature as the main amp. If you put in a tube that is "not the best in the low end", the low end will not be the best. I just find 6550's and EL 34's to be more linear top to bottom than the other two, and 6550's have the best bass weight and slam of the bunch. I admit that I may not be not a "classic" tube sound guy as I have been trying to rid my system of some of what I feel are limitations of the "classic" tube sound while keeping what tubes do best in my mind.

Rec's system seems very nice! I would like to hear that combo myself.I love the look of that amp too! Rec, did you have the speakers low end adjusted with that amp when they were set up?
The 5's have room compensation bass EQ built in and may be able to make up for some bass colorations of different tubes for those of you that are not as up on the 5.

Ras10, much more important than which tube you choose( as they all are good in their own way) is what you use for a X-over for the 5. Do you have the expensive model 5 x-overs? If you don't and are using the fixed value X-2's it won't matter how many different tubes you try or how much you spend on Cryo treated NOS tubes. All your signal goes through that X-over and will make or break the final result. Did you just get the amps and the speakers? Did the dealer already set up the bass EQ for you?

Creeper, the Svetlana 6550c is what I use in my amp.It was voiced with those tubes though so I leave well enough alone. I hear that in the right amp the Electro Harmonix 6550 is very good too. But it has to be the right amp! A friend tried them and a first it was great, as they burned in though the sound got real thin and nasty over the course of a few weeks. He has an ARC VT60. He asked ARC about it and they told him that they had the same results with the Electro's in the VT100. Seems to be a lot of variation in different brands, let alone different types of tubes. Makes a recomendation for someone else pretty complicated.

Creeper, if you wan't to do some reading about the way the powered woofer on the 5 is set up, the review in "The Absolute Sound" explains it quite well. It can be found at the Vandersteen web site. I realize after some reading myself that the Vandersteen 5 comes with the model 5, high pass filter, that goes between your amp and pre-amp.I understand that these are very transparent unlike the crappy little WX-2 supplied as a temporary filter for the 2Wq.

Kana813, I have been wondering the same thing about the Vandersteen you are talking about, I though it was called the Reference Monitor. We will have to wait and see.

Using a high pass filter before the main amp with the 5's(and with the 2Wq, which I have) gives you the true benifits of bi-amping, since the main amp has the low bass filtered out. Using the speaker signal from the amp lets the built in sub amp take on the character of your main amp so that they don't sound like two distinct and different things, and keeps the blend more seemless. That's why Rec can get away using the amps in triode for 50watts. Same reason I can use a 45 watt amp and the 2Wq with 2Ce's(which are rated at the same 87db sensitivity as the 5)to get fairly realistic levels

Rec, seems the most info that can be found on the update from the Model 5 to the 5A, is in the adds in both the latest Stereophile and TAS. The add states,"a switch-mode power-factor corrected amplifier supply, a proprietary woven-cone midrange with high-efficency magnet assembly,a new tweeter utilizing a more aerodynamic magnet structure and die cast alloy chassis, and the requsite refinements in the crossover.."

I know the NOS guys will scream bloody murder, but I think that the current crop of Svetlanas and some of the Electro Harmonix tubes are they way to go. A dozen output tubes can be expensive, NOS output tubes are down right precious. El34's will end up costing as much as KT88 since you will chew them up twice as fast and still get 1/2 the power while doing it. I still say Svetlana 6550c's are the way to start for what I feel is the least flavoured sound of the lot,or if you like a more romantic (classic tube) sound get the KT's. Check out www.thetubestore.com, they have some good info on the site and they may be able to steer you the right direction. They have some NOS small input/driver tubes like 12AU7 but I didn't see that they had any 12fq7's at all. If you give them a call, they may have feedback from other users of your amp and what works best.(did you ask Quicksilver?) The guys at the tube store are great people to do business with and have fair prices. I got driver tubes from them that one of my old amps didn't get along with and the exchanged them for me, which I thought was great! If you really want exotic NOS talk to Andy at Vintage Tube Services. Have fun!