Yes it is OK to mix SS pre-amp and tubed amp. Not usual but certainly OK and as far a matching it can be much easier.
You replace tubes based on usage. Normally power tubes last from anywhere between 1500 and 3000 hours (depending on amp design) and small tubes last much longer depending a lot on tube quality. Anywhere from 5000 hours and up.
Tube are generally easy to find, especially new production tubes. NOS is harder and more expensive. Try to find an amp (for your first amp) which can use popular new production tubes such as EL34s, 6L6's, 6550's, and KT88's. Power tubes cost between $60 to $160 a quad depending on type. Small tubes cost anywhere from $10 to $20 each depending on type and quality. You buy them from on line tube dealers with a proven track record for reliability. Easy to do.
Small tubes are easy to replace. You simply pull them out and plug in new ones. Power tubes can be easy and the same as small tubes if you amp is of the auto biasing variety. If not, you have to have a volt meter and learn how to use it and adjust the bias yourself. Not a big deal, especially if your amp has a bias pot for each tube.
You certainly do not have to take your amp into a dealer for tube replacement, provided you buy one that has a reputation for being easy for a beginner to handle. Some amps, especially older ARC amps for example can be a real PITA even for folks who know what they are doing so be wary of the amps requirements.
FWIW, and I know you didn't ask, but ARC is not really known for making the best SS pre-amps, and if you're are really going to get the benefit of a tubed system by putting tubes at the amp end you want to be sure you get the most transparent and tonally neutral pre-amp you can afford. Cheap out on this and you won't really hear a great benefit from using contemporary tube amps.
Take your time, do a LOT of research, and ask a LOT of questions before you jump in.
You replace tubes based on usage. Normally power tubes last from anywhere between 1500 and 3000 hours (depending on amp design) and small tubes last much longer depending a lot on tube quality. Anywhere from 5000 hours and up.
Tube are generally easy to find, especially new production tubes. NOS is harder and more expensive. Try to find an amp (for your first amp) which can use popular new production tubes such as EL34s, 6L6's, 6550's, and KT88's. Power tubes cost between $60 to $160 a quad depending on type. Small tubes cost anywhere from $10 to $20 each depending on type and quality. You buy them from on line tube dealers with a proven track record for reliability. Easy to do.
Small tubes are easy to replace. You simply pull them out and plug in new ones. Power tubes can be easy and the same as small tubes if you amp is of the auto biasing variety. If not, you have to have a volt meter and learn how to use it and adjust the bias yourself. Not a big deal, especially if your amp has a bias pot for each tube.
You certainly do not have to take your amp into a dealer for tube replacement, provided you buy one that has a reputation for being easy for a beginner to handle. Some amps, especially older ARC amps for example can be a real PITA even for folks who know what they are doing so be wary of the amps requirements.
FWIW, and I know you didn't ask, but ARC is not really known for making the best SS pre-amps, and if you're are really going to get the benefit of a tubed system by putting tubes at the amp end you want to be sure you get the most transparent and tonally neutral pre-amp you can afford. Cheap out on this and you won't really hear a great benefit from using contemporary tube amps.
Take your time, do a LOT of research, and ask a LOT of questions before you jump in.