tube preamp w/ solid state amp

are there any problems in using a tube preamp with a solid state amp? any guidelines in mixing tubes and solid state?
thanks in advance
none at all. I've been doing this for some time. The only guideline I follow is whether I'm satisfied with the sound. There are rules of thumb for impedance matching (I don't recall what they are, but you can probably find them with a search).
There is nothing inherently wrong with running tube preamp/linestage into solid state or vice versa. Some tube linestages have a high output impedance and should be matched to a linestage with a high input impedance. That is typically the case with a tube amp, but not necessarily the case with a solid state amp. A mismatch may result in frequency response being less than totally flat.

The other consideration is a practical one. Solid state gear takes a VERY long time to warm up, but draws relatively little current at idle, so a lot of people leave solid state amps on all the time. A tube linestage should be turned off when not in use. That may create problems because one should NOT turn off an on components in front of an active amp (could result in very loud noise/damage to the speakers). One would need to find a way to mute the output of the linestage or input of the amp if the linestage is to be turned off and on while the amp remains running all of the time.
Krell power amps require a modification to run safely with a tube pre. I believe a resistor of some sort is put in the circuit to avoid some nasty situations, oscillation I believe, but don't quote me on that last detail!
Larryi makes a good point regarding the order of turning things on. If the main amp(s) are on already, or even switched on at the same time as the pre-amp, you could easily get a lot of nasty noise as the tube pre powers up. It is not something you want to hear from your nice speakers. The simple solution is to turn your amp on a few moments after turning the pre on.

Also, I am no expert on the matter, but Gill Audio did change some parts in my tube preamp (a Gill Audio Alana) specifically because I use SS amps - in my case Theta Enterprise monos. As Larryi also mentions, this may have to do with the impedance matching, I really don’t know. When I spoke to Gill about my preamp, they suggested these changes to what was already in there based upon my amp. The resulting improvement to what I thought was already a stellar preamp was very noticeable.

FWIW, they also added a time delayed 12v trigger. When I switch on my preamp, it will activate the 12v trigger about 20 seconds later so that the pre will be fully powered up by the time the main amps are triggered on. One switch does it all.

I regards to Pbb's comment, I believe the Krell “modification” is because it is direct coupled from the factory. This “modification” is user serviceable and is meant to protect the amp from DC leakage that can happen with a tube preamp…at least this is how I understood it when I had a Krell amp before my current amps. I never did this and never had a problem, but better safe than sorry – if you have a Krell, do some investigation first.
I've used tube preamps with solid state amps for several years now. I was carefull about turn-on and turn-off sequence at first, but found three of my preamps could be turned on and off while leaving the amp on with no ill effects. They were a BAT VK-31SE, Kora Eclipse, and Audio Research Reference TWO mk II. With the Audio Research preamp I do mute it before I turn it off. The Kora had a built in "warm-up while muted" turn-on sequence. I left the BAT in standby mode so when you turned it on it had a short warm-up delay and then was ready to go. I would think the amp you partner it with could make a diffence in the behavior, also.
I have done this for 15yrs now. The two things you need to be concerned with are; some tube preamps output impedance are high and or are high at the freq. extremes. If you match that with a SS amp with a low input imp. it will cause the amps freq. output to deviate. Second it is good practice to mute your tube pre, then turn off the amp, then the tube pre.
I ran a Conrad Johnson pv10a pre along with a Classe DR-9amp with very good effect with excellent sound while it all ran a pair of Sound dynamics300ti,MGIII,and numorous small british speakers.
The general rule of thumb is the input impedance of the amp should be at least 10x greater than the output impedance of the preamplifier - this is almost never an issue when using a tube amp which genrally, but not always, 100kohm input impedance. Generally only a consideration with 10Kohm amps (some Pass amps for example), but it is said that the greater the differential the better. Ofcourse, theory ain't worth a darn compared to trying it out and "specs" can be misleading and don't always tell the full story.
I am using a McCormack DNA-125 and Manley Shrimp with no problems. Talked w/Steve McCormack prior to buying the Shrimp and he said there would be no problem mating the two but for the sensitive volume attenuator on the Manley which only allows me to turn up the pre to about twelve o'clock.
I run a tube pre and solid state amps with no issues. The pairing sounds really good. Also, no issues with the sequence of turning off amp and preamp.
Tube preamps can play more detail in a relaxed manner than their transistor counterparts. Once lost, you can't make up for it downstream so yes, a tube preamp is a good idea with a transistor amp.

Of course, I think a tube amplifier is a nice move too :)
I have been using ARC ref 1 with a krell with no problems.
The ARC ref has no DC leakage, because they use coupling capacitors to eliminate the issues. I have tried many different set ups and to tell you the truth nothing is more true than those 2 combinations. There are certain sound tracks that actually sound like the performers are in the room.This is my opinion.

Happy Listening...........