Tube preamp with or without phono stage?

What variables of interconnection are being referred to here?

The issues are the sound of the interconnect that you have to use with an external phono section, how well its power supplies are built, how well its grounded and so on- just like what happens when its built-in.

some manufacturers of very good sounding preamps install a phono section as after-thought or they don't install one at all. I realize that this is not always the case but I am very satisfied with my external phono preamp.

Good!- and very true- like I said, its all about intention!  I've experienced some of the preamps as you describe above and one of them had a phono section so bad that I'm convinced one of those off-the wall phono sections Radio Shack used to sell in a bubble pack would sound better :/

We've been asked to do an external preamp quite often. The way we see it, the biggest issue is the connection to whatever the phono section is driving. Some people don't want to have anything to do with digital and in a purist way want to hook the phono section right to the power amp. To really do that right, the output of the phono section has to have enough voltage to drive the amp to full output and also have some sort of volume control system. Right about that point a full-function preamp starts to make a lot of sense! We've been doing balanced line with our preamps in order to eliminate the 'sound' of the interconnect cables involved, but in order to do that the circuit that drives the output has to have some guts (our preamps can drive 600 ohms no worries and is a direct-coupled output); if you are going through that trouble to build that into a phono section so you can do the hookup properly, at that point you have 99% of what a full-function preamp is already!

We built our preamps to essentially be stand-alone phono sections that can drive power amps properly but we added enough switching so that the line drive can be used as a line section. Anyone that knows me knows that I really am analog first; heck, I don't even have a digital setup in my home system.

There is only one advantage of having a built-in phono and that is, it saves space, one less box. However if you are looking for the ultimate sound you will find a quality external phono head amp is the only way to go if you're serious about good sound! Here is another thing, if you are not using the internal phono preamp, do not remove the tubes from the circuit for safe keeping as this will damage the phono circuit.

I don't find this to be the case. The problem is the connectivity- if the phono section is built-in you don't have a connectivity issue. But if its external you do, which means the cable has to do a pretty good job.

You can certainly install a first class phono section in a preamp. Its all a matter of design; that preamp should be easily capable of keeping up with an external unit. What matters is not whether the phono preamp is internal or external so much as the intentions of the designer.

I also feel cables and vibration control make a difference so take that into consideration.

This is a pretty big argument for having the phono section built-in.