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

@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...

@tubegroover , just FWIW, bypassing an existing coupling cap is often a bad idea. I don't doubt that you enjoy how the unit sounds now, but I strongly suspect that if you had cutf V-Caps of the correct value as used in the stock cj that it would sound even better. It is often the case that bypassing coupling caps can result in smearing (especially at higher frequencies); for this reason it usually seems best to give the coupling caps your best shot with a single part.

The Harmon Kardon Citation 1 preamp is excellent when properly restored. To find one like that would probably be more expensive than the preamps listed, but it can keep up with them easily. A very competent circuit!

The Dyna PAS-3 is not a particularly great preamp, but it lends itself very well to update and modification! I've seen them be giant-killers on many occasions. We've done mods on them for decades and our UV-1 is heavily based on those mods. You can find used PAS-3s for $200-$400 depending on condition- and likely they will need refurbishment at that price.

Our own MP-1 has been in production since 1989. So I guess that can qualify as vintage; it features a direct-coupled output that allows it to be quite transparent; the real issue is whether you can find one.