4 ohm vs 8 ohm taps

Yes, it is a try and see kind of thing, but the 4 ohm tap will always have lower impedance which will translate into better damping of the speaker, no matter what impedance the speaker is. This will not always sound "best" and using a 4 ohm tap with an 8 ohm speaker will sometimes diminish the power output. I say "sometimes" because the interaction is complex and many 8 ohm speakers drop down pretty far at a given frequency, as mentioned above.

I use the 4 ohm taps on my VAC amp, and I'm using speakers with a 6 ohm nominal load, that dips to 3 ohms in the lower bass. I've also tried the 8 ohm taps.

If you have an 8 ohm speaker, use the 8 ohm tap. If you use the 4 ohm tap, the transformer will not be loaded correctly and will 'ring' that is to say it will add distortion, which usually makes the amp sound brighter (though not always).

Conversly, if you put a 4 ohm speaker on the 8 ohm tap you just cut the load that the tubes see. For example if the tubes are seeing 3000 ohms 'plate to plate' the impedance just dropped to 1500 ohms. This will cut power (maybe by as much as 1/2) and add distortion! Transformers are called that because they transform impedance and that goes both ways.

Funny, but the construction manual that came with my Dynaco 70, which I built in 1970, indicates that putting 8 ohm speakers on the 4 ohm taps, while reducing the max power available due to less power transfer, will give LESS distortion and if max power is not a concern then that is really the best way to connect the speakers, if in doubt.
Bob P.

Don't mean to hijack this thread in any way, only hope to augment it because I have a similar question. I have 2Ce Signatures and I see in the product literaure that the nominal impedance is 7 Ohms and the minimum is 4 Ohms. So what really makes sense from a rational standpoint which taps should I use? I'm hoping to hear something other than, "whichever sounds best." Thanks!
Steve