4 ohm vs 8 ohm taps

inpepinnovations@aol.com...How can you say that a zero ohm load is "seen" through transformer coupling, but yet loudspeaker loads are not?

In another area, when you use a step up transformer for your moving coil phono pickup it can be connected to a standard MM preamp input, 47K input load, and still present the proper loading of a few hundred ohms on the pickup. The loading applied to the secondary is "seen" through the turns ratio of the transformer.
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Been using the 4 Ohm taps from the beginning and will stick to that. Thanks!

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.

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inpepinnovations@aol.com...An 8ohm speaker on the 8 ohm tap, and a 4 ohm speaker on the 4 ohm tap will look the same to the tubes driving the primary. (That's why different taps are provided). If the 8 ohm speaker is on the 4 ohm tap or the 4 ohm speaker is on the 8 ohm tap the tubes will see an impedance that is not what the amp designer wanted. Whether this will be enough to cause significant distortion, and if so, how much, is a question I will leave to the amp designers like Atmaspere.
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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.