8 Vs 4 ohms

If you load the 8 ohm tap with a 4 ohm load, the plate to plate impedance that the tubes are supposed to be driving will be reduced. This will result in less power and increased distortion (the 'loosness' that others have mentioned).

This is harder on the tubes, as the loss in power is dissipated in the tubes themselves.

The transformer will also be over-damped, resulting in a loss of high frequency bandwidth.

Ultimately, if you are investing in a tube amplifier (*any* tube amplifier), your tube amplifier investment dollar will be best served by a speaker that is at least 8 ohms as opposed to 4, all other things being equal.

If you can go with 16 ohms things get even better, but some amps these days don't have a 16 ohm tap, which is really too bad.

The interface between the amp and speaker is paramount to getting the performance out of any amplifier, transistors included.

Hi Eldartford, actually the 16 ohm tap is twice the number of turns as the 4 ohm tap. The 8 ohm tap is in between. The impedance of the winding goes up by the square of the number of turns. So the 4 ohm tap is the center tap between 0 and 16.

Also, the voltage of the 8 ohm tap is higher but it is not double! The difference is about a factor of 1.414, assuming that you have the same amount of power into your speaker loads of 4 and 8 ohms and the taps are properly loaded.

If you put a 4 ohm load on the 8 ohm tap the tubes will not be able to make the right amount of power and it is possible that your output voltage may go down rather than up. This depends quite a lot on the way the output section is constructed.