OK, so obviously his amp tech likes the V30, but needs to update his skill set just a bit. Your Rect-O-Verb, probably just like the one I own, is a 50 watt amplifier and the tech, after being told the 80 watt speaker that came with the amp is blown, recommends a 30 watt speaker. Will it sound good? Maybe, but that's for you to decide, and if you haven't heard one or if you can't compare them or know someone who has then why buy a speaker that may or may not work for you.
Speakers are rated in many ways. They are rated for mechanical excursion, frequency response, power compression (heat), senetivity, and many other properties as well. When rated for power many companies cheat and may list "program power", or "peak power handling". Those aren't actually a rating, but a mathmatical guesstimate based on the actual power rating of the speaker when tested to a specific input voltage for a specific period of time.
JBL tests their speakers using pink noise and a signal equal to the speakers advertised power rating. Therfor, any JBL speaker you buy will have had the power rating proven by testing that design for 100 hours (In most cases) So, if the JBL speaker you buy has a power rating of 30 watts it indicates that JBL has pushed the speaker with 30 watts RMS power for a period of 100 hours.
Now the rest of the world. The speaker recommended by your tech is rated at 30 watts, so we'll take that to mean 30 watts at 8 ohms continuous. That means that if you can limit the output of the ROV to 30 watts the speaker should last forever.
In the real world not only is that not practical, but it's impossible, hence the term "program power". Program power is a rating used to describe the power handling of the speaker as it handles programmed material and could be anything depending on that material, but in the case of pro sound and guitar speakers usually means twice the RMS power handling capability of the speaker.
But please note that "program power" is not a forever rating. Program power usually equates to a duty cycle of 10% at best and that means for every 10 minutes you play, the speaker will handle peaks to double it's designed output for about 1 minute of time. That's the period of time when the speaker really starts to compress nicely and that good grind starts to happen. And guess what? We want that sound almost all the time. And to get that sound we push the hell out of our speakers. Or do we? Usually not, because most people just reach the point where damage could occur, and most speakers today are made much better than they were when I would blow them up on a steady basis. But still, that ROV, or any good 50 watt tube amp, can produce peaks well in excess of 100 watts output. My recommendation, if you want that british sound, would be a Weber ceramic 50 watt Blue dog. You'll be safe, and you'll be happy. (But listen to one first if you can.)
And please be aware that if you add a second speaker to the formula the power handling capability is doubled but that the output is not. The speaker will in theory give you a 3db increase in gain without doubling the power of the amplifier. 3db is generally considered to be the lowest increase in audible sound the ear will detect easily.
