4 ohm vs 8 ohm taps

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.

Eldartford, you know of course that the secondary on the transformer has different taps, 4, 8 and 16 to match the speakers. Those taps simply have different amount of winding to 'transform' the primary winding impedance which is constant. The tubes themselves don't see the secondary taps or impedance.
Salut, Bob P.

Eldartford, I think that we are saying the same thing, but not understanding our explanations. I never said that the tubes 'see' a 0 inpedence. We both agree that the transformer effectively isolates the speaker load from the load imposed on the tubes, i.e. the tubes 'see' a constant (high impedence of the primary windings on the tranformer) regardless of the speaker load and regardless of the tap used for the speaker. If an 8 ohm speaker is attached on the 4 Ohm tap, however, the power transfer is not as good as using the 8 ohm tap, but the level of distortion should be lower and the damping factor higher. The tubes never 'see' this, which was the claim made by the original poster (Atmaspere, I think) that using the lower tap would cause the tubes to 'see' a different impedence and thus distort.
Salut, Bob P.

Eldartford, this is where we disagree. If the 'wrong' ohm speaker is attached to the wrong tap, the tubes DO NOT see a different impedence at the primary. The tubes continue to see the primary winding impedence, whose impedence remains constant regardless of what impedence speaker is attached to whatever tap. The power transfer from the transformer to the speaker, however, is affected and also the distortion because of the mismatch of impedence on the secondary windings to the speaker. Due to this mismatch of power, the volume might not be sufficient and the operator then increases the gain at the tubes, perhaps driving them into distortion, but it is not because of the impedence changing on the primary side.
Salut, Bob P.

No, Eldartford, the person saying that attaching an 8 ohm speaker to the 4 ohm tap will cause distortion because the tubes will 'see' a different impedence than if the speaker were attached to the 8 ohm tap, is wrong! When in doubt, use the lower tap, the worse that will happen is a loss of ultimate power transfer, but with lower distortion.
Respectfully, Bob P.

Stevecham, use the 4 ohm taps.
Atmasphere, further to my other note, the tubes don't 'see' the impedence on the speakers, but the impedence on the primary of the transformers, which DOES NOT change with the whichever taps one uses on the secondary.
Bob P.

Eldartford, exactly - the tubes do not see the difference of what is connected to the secondary taps or to which taps the speaker is connected. The poster that said that connecting the speakers to the 'wrong' tap would make the tubes 'see' a different load and thus distort their output.
The reason that the amp overheats when shorting the speaker taps is due to the tranformer trying to drive a 0 inpedence load and thus drawing more power from the tubes on the primary side. It has nothing to do with the impedence changing on the primary (which doesn't), which the tubes 'see'.
Salut, Bob p.