How powerful is a Wavac MD-300B

I listened to that Amp a few years ago but with a 99dB speaker....that was ok.
The 300B does not have the abilities to Drive unsensitive Designs, 93dB is normally not enough for such amps but you should try first.
I listened to Westminster speakers also with 200w, their owners wanted it that way.....

Hi Pani, I have a pair of Wavelength Cardinal XS @ 10 watts (& Wavelength 45s) in a 12' by 15' room (somewhat open on one side) My speakers are Beauhorn Virtuoso w/Lowther DX4 (106, with MORE than enough volume) You really need to borrow or have someone bring over quality 300Bs to try or at least buy used.

Pani,
The problem is that the power rating doesn't tell you much. There is a
hierarchy that exists in the ranks of 300b amplifiers , based of quality of
construction, power supply and transformers. This is why one will drive a
particular speaker well and another ( same stated power rating will
struggle). The two WAVAC SET 300b amps may have the same power on a
test bench but likely sound "very" different and vary in their drive
capability.

I don't agree with the blanket statements made about these amp's
limitations, you must consider which 300b amp is in question for reasons
already explained. My 8 watt SET drives my 94db/ 14 ohm speakers easily.
Isochronism is right, at some point you simply must get these amps on
your tannoy and find out for yourself.

I have a 300b Jolida amp that sounds much louder than the 8 watts would have you believe. It might be because of the structure of the harmonic distortion. Our ears/brain judge volume in part by certain distortions. So I appreciate that it "sounds" louder without actully being at a higher SPL. I figure it is saving my hearing!

Speaker/amp matching is, IMO, much more critical with a 300b SET so I also recommend that you try the 300b amp with your speakers if possible before purchase or get confirmation from others that are using your speakers with a 300b amp.