I have a tube amp question?????

I once owned a 30 watt tube amp that I used to drive Vandersteen 2c's (88db) in a 12 by 26 room. It occaisionally clipped and distorted so I would think that 12 watts would not be enough, however this is only my opinion.

I doubt that 12 watts into the given speaker load you described would be very satisfying. If I couldn't audition I wouldn't do it.

Here's a possibility. Get your hands on a scope or someone with one. Hook up any kind of amp or receiver that is greater than 12 watts. Now power is equal to Volts squared over Resistance. The amp was probably rated at 8 ohms. This computes to about 10 Volts RMS which is about 14 volts peak. That's 14 plus and 14 minus. Hook up the scope to the speaker terminals and see how often you exceed 14 volts while playing music at a level that is satisfactory.

My guess is that you won't be happy.

12 watts is to small for an 87db speaker unless you are using it for light background music.

I use 8 watts of 300B on 92db speakers with good results. Not a wall shaker but I don't like real loud music. The same 8 watts is not enough for a 90db speaker.

15 watts will do 90db quite well.

Hi, Tireguy, there is a guideline for power:
the efficiency of your speaker is 87 db means with
1 watt input, they will produce 87 db sound if you
measure sound pressure on axis, 1 meter away from
your speakers. If you want to increase 3 db, you
need to double the power of your amp. For example,
you need 2 watts to get 90db, 4 watts to get 93db
and so on.
I hope this will help you a little.