It is a good idea to purchase a vintage tube pre-amp.

The problem is how to keep good maintenance of the vintage gears.  Some parts are hard to find, some changes might change your sound reproductions. Also, judging on it's rare quantity, it is hard to find the right, experienced, dedicated engineer to fix it.  

Ralph I have no doubt that having the correct value caps would be ideal however I’m not even sure that Vcap makes the cutf capacitors of the value required, 20uF X 4. In any case the cost would be prohibitive if they do which I don’t see on their web site. If there is any smearing relative to the stock polystyrene caps, it isn’t evident to me and as stated, there was significant overall improvement along with numerous other upgrades by Bill Thalmann.

Conrad Johnson has a teflon cap upgrade but if I spent what they were asking for their upgrades one might question the sanity of going that route, it sure didn't make sense to me.

Just received my Linear Tube MicroZOTL2 and it is stunner as a preamp right out of the box! Anyone looking for a preamp under $2,000 should give this a listen because it is amazing. It also responds to Tube rolling. I immediately put Tungsol Round plate 6sn7's in it and it plays music better than anything else I have ever heard! It only has three inputs and the remote will only adjust volume, but this piece is one of the great bargains in audio. I have heard most of the preamps in this thread and my opinion this is the best of the bunch! The tonality and imaging of this preamp (headphone amp actually) is just spot on. You really don't need to spend any more for world class performance. I want to give a shout out to Teajay who first introduced me to this preamp.

@tubegroover , are these caps at the output of the preamp? If so, what sort of amp are they driving?

A very common issue that faces preamp manufacturers is the value of the output coupling cap. This is often defined by the lowest impedance that the unit is expected to drive (and certainly is a dilemma as smaller caps almost always sound better than large ones). But if you are driving a tube amp the caps might not have to be so large! Just a thought- its easy enough to calculate the right value given the input impedance of the amplifier...

Yes Ralph, the caps are at the output driving a pair of Quicksilver amps with an input impedance of 100K. I also have used with a pair of vintage MC60's and  a Berning zotl amp to equally good effect.