8 Vs 4 ohms

Djk: I have a Cronus at 55WPC and found that the 4 Ohm setting sounded better with my Vandersteen 2Ces, which are above 4 Ohms nominally but still have a minimum impedance dip to 4 Ohms. The bass is better and there is a better dynamic punch. Do you know what the minimum impedance is for your speakers? If it is less than 4 Ohms and it probably is, then I would go with those taps.

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.

Thanks to all for the advice. The speakers are Dali Helican 400's at 4 ohms. I think I will switch to the 4 ohm tap and see what happens. It sounds like that would put less stress on teh amp and perhaps better sound?

Dan

DJK let us know the outcome.

inpepinnovations@aol.com...If the 4 ohm and 8 ohm taps have the same voltage (per your comment) why do we have two taps?

Actually, the 8 ohm tap has twice the windings of the 4 ohm tap, and puts out twice the voltage as Cford noted. So, for a given setting of the volume control, the amp will play louder. But it will clip at lower power because the output tubes are not optimally loaded. This may also increase distortion.