The 2215 is actually a very good scope to use with tube gear. It has an input range of 400V which is extremely high for solid state scopes.
Does it have any probes with it? If not you will need to get some. For use with tube gear you need to get probes that can handle the voltage. The "standard" 10X probe can usually handle 600V which is fine for a lot of tube work, at that max of 600V it is delivering 60V to the scope. You have PLENTY of margin there with a 400V input range! With that 400V range you won't fry the scope if you run direct without a 10X probe.
You can also get 1200V 100X probes, these are great for tube work and not very expensive. If you know you are going to be doing a lot of audio tube work with the scope these 1200V 100X probes would probably be a good investment. No matter what you did you probably would not fry anything.
There are also high voltage differential probes, these are great but not cheap, several times the cost of the scope. But for some things they are one of the few ways to see what is happening. (for example put one connection on the cathode of a tube and the other on the plate to see what is happening across the TUBE, not between ground and the plate). For example I have an amp where the cathode of a power pentode is bouncing around all over the place and I want to see what is between the cathode and the screen, the differential probe is great for this. They are also completely isolated from the scope, thus there is no risk of shorting something out to the scope ground. See below on this aspect.
Two words of warning when working on tube circuits, the ground wire on the probe is connected to the mains ground pin, be EXTREMELY careful where you connect this on tube gear. If where you connect it is NOT connected to mains ground (say a couple hundred volts) you can easily fry your scope probe, your scope, the tube circuit you are working on and maybe even you. (this is one reason I REALLY like a high voltage differential probe)
Number two, hook up the probe to what you want to test with the gear OFF, make sure the probe is going to stay where you put it, THEN turn the power on the gear. RESIST the temptation to hand hold a probe and go poking in around a live tube circuit. If you don't heed this you WILL destroy something, somewhere along the line.
I don't want to scare you away from using the scope, just be mindful of the high voltages, get probes that can handle what you are working on and think carefully about what you are doing.
If you are going to be working on gear for which you don't have a schematic or are not familiar with the circuit, one of those high voltage differential probes might be a really good investment. That issue of connecting the ground clip to something that isn't at ground potential is a serious issue when working on unknown gear, the differential probe completely gets rid of that issue.
John S.
