Switching to tube amps

Hello guys. :)
I'm new here.
I'm looking to switch from solid state to tube amps. I was never much of a gear guy so i don't know much of tube amps except for their big, fat sound. My experience with these is minimal. I've only used them a few times in some reharsal rooms. I remember a Peavey head(don't know which model) hooked up into an Engl cab, killer tone. Not being a gear nerd, i had few pedal effects(which i've sold anyways, didn't use them). I've been playing for 8 years and a half, all this time I had my guitar plugged straight in to the amp and that's about it.
My current gear:
-Ibanez RG7321 (SD-SH8B pickup in bridge) -old guitar but it plays nicely, no need to change.
-Randall RX30D - old too, fairly good tone, but never let me down.
-Hardwire TL-2 - distortion pedal.
-Line 6 audio interface, for recording stuff.
That's it.
I'm in a band now. My trusty Randall is alright for reharsal, but live is out of the question. (low power, not enough bottom end, etc.)
So, i need(want) a tube amp. I know the good ones are (very) expensive. The cheaper(i.e. Marshall MA50, Peavey Valveking 100) are .... well, not worth it. If i'm still going to invest a fairly large sum of money(for me, at least), i want something on the medium, higher-end side, so i'd go for used ones. I've found a used Blackstar HT100 Head for ~550 $ in my area, which is a good price, i think.
Problem is, i don't know how and what to test and check on them before buying. How do i check if the tubes are in good condition? How do i know when a tube needs to be changed? What else is there i should know? Head + cabinet or combo?
Conclusion is, i need an amp which packs a punch and can improve the overall sound of the band or recordings. I want a good tone for metal.
Thanks and sorry for complete lack of knowledge, but i have to start somewhere :)

Hi Lawgeenoo,
Unfortunately tubes don't come with an odometer so to speak. Preamp tubes are typically good until they don't work (light up) then they need to be replaced. Nothing wrong with experimenting with different brands of pre amp tubes to get different sounds and feel. The larger power amp tubes are where this is a little more risky. Even if you have to replace all the power tubes..depending on the amp's overall condition it still might be a good deal. Power amp tubes should be replaced (the entire set) regularly depending on how much you play. If it's mainly on the weekends and a rehearsal or two a week…I'd say about 12-18 months. If you play several hours a day every day I'd slide that to 6 months. The problem is the tube degradation happens so slowly you typically won't notice much of a change. Depending on the amp…it may need re-biasing (some amps do this automatically) which should be done by an experienced technician. Good luck!

Hello guys. :)
I'm new here.
I'm looking to switch from solid state to tube amps. I was never much of a gear guy so i don't know much of tube amps except for their big, fat sound. My experience with these is minimal. I've only used them a few times in some reharsal rooms. I remember a Peavey head(don't know which model) hooked up into an Engl cab, killer tone. Not being a gear nerd, i had few pedal effects(which i've sold anyways, didn't use them). I've been playing for 8 years and a half, all this time I had my guitar plugged straight in to the amp and that's about it.
My current gear:
-Ibanez RG7321 (SD-SH8B pickup in bridge) -old guitar but it plays nicely, no need to change.
-Randall RX30D - old too, fairly good tone, but never let me down.
-Hardwire TL-2 - distortion pedal.
-Line 6 audio interface, for recording stuff.
That's it.
I'm in a band now. My trusty Randall is alright for reharsal, but live is out of the question. (low power, not enough bottom end, etc.)
So, i need(want) a tube amp. I know the good ones are (very) expensive. The cheaper(i.e. Marshall MA50, Peavey Valveking 100) are .... well, not worth it. If i'm still going to invest a fairly large sum of money(for me, at least), i want something on the medium, higher-end side, so i'd go for used ones. I've found a used Blackstar HT100 Head for ~550 $ in my area, which is a good price, i think.
Problem is, i don't know how and what to test and check on them before buying. How do i check if the tubes are in good condition? How do i know when a tube needs to be changed? What else is there i should know? Head + cabinet or combo?
Conclusion is, i need an amp which packs a punch and can improve the overall sound of the band or recordings. I want a good tone for metal.
Thanks and sorry for complete lack of knowledge, but i have to start somewhere :)

Most venues have you mic up your gear anyway. I wouldn't worry about not enough volume... However, depending on where your overdrive tone comes from, you can get a loud clean amp (Fender Hot Rod Deluxe) and use a overdrive/distortion pedal in front of it.
However, I've used a Peavey Bandit 112 (solid state 1x12 80 watt) on stage and its louder then most amps and sounds great.