Connecting 2 sets of speakers to a tube amp

I don't think that would be a good idea with most tube amps. That would be seen by the output tubes, on the primary side of the output transformer, as if a single 2 ohm load were connected to the 4 ohm tap. That would seem very likely to degrade sonics, with damage also being a significant possibility.

The stress on the amp would be lessened a bit if you connected both speakers to the 4 ohm taps, but in that situation the amp would be seeing a load of 2.67 ohms on that tap, which still seems very excessive.

And of course there are most likely some frequencies at which the impedances of the speakers will be significantly less than their rated 4 and 8 ohm nominal values.

Regards,
-- Al

What I have done with my tube amp (Ayon Spirit II) is utilize the pre-out and send that signal to a second integrated amplifier through which I power a second pair of speakers. My tube amp powers the 4 ohm speakers (Montana EPS2's) and a McIntosh integrated powers my back speakers (8 ohm Vandersteen 2a's). This prevents entirely the problems that Almarg mentioned above. Further, with two integrated's I can taylor the front vs. back speakers beautifully. Running two channel 4 speakers makes the system sound DRAMATICALLY larger, more full, and realistic with vastly superior sound stage. The difference between the 2channl/4 speaker and the 2 channel/2 speaker is staggering (akin to tripling system cost or more)

So... that is what you should consider doing. Of course, your tube integrated needs to have a pre-out to do it...

Thank you for your help. I will use the pre-out to a second amp.

Marty (Viridian), note that the speakers are different models, one being rated at 4 ohms and the other at 8 ohms. Series connection of different models will usually result in significant sonic degradation.

How the voltage and power being output by the amp at a given frequency at a given time will divide up between the two speakers depends on the relation between the impedances of the speakers at that frequency. Therefore the frequency response of each speaker will be affected in an arbitrary manner by how the impedance of the other speaker varies as a function of frequency.

Another factor that might also be an issue with a series connection is that the 8 ohm speaker will receive considerably more power overall than the 4 ohm speaker. Based on the oversimplified assumption that the impedances of the two speakers are purely resistive and correspond to their 4 and 8 ohm nominal ratings, the 8 ohm speaker would receive twice as much power as the 4 ohm speaker.

Regards,
-- Al