Amp & Speaker matching

Not sure I agree with Larryi.

The output transformer in a tube amp reflects the load impedance back to the the tubes. If you use speakers rated at a higher impedance than the output transformer impedance things will be ok. You will just get lower output.

If the speaker impedance is lower than the output transformer impedance then the tubes will draw more current than if the impedances were matched.

Whether or not this is a problem depends on the amp's design limits. Consequences range from none to damage such as blown output transformer, blown tubes, or worse, depending on amp and the amount of the impedance mismatch.

Check with your amp manufacturer for advice.

R Burke,
In my opinion the higher the speaker impedance the better for tube amplifiers,i.e. easier load to drive and generally less distortion. You should not have any problems.Low impedance speakers can be a 'potential' problem for some tube amplifiers.

Manley and VTL set their output transformers to approximately 5.5 ohms so their amps will perform well with 4-8 ohm speakers.

If you run a 16 ohm speaker on an 8 ohm tap, you may get around a 3 decibel loss in volume. On some amps, this can be a risk. It depends how they wound their transformers, and to what impedance they're loading the tubes to, plus other design characteristics in the amp. I would ask first to be safe. Some amps may be fine this way, others won't be. When the speaker impedance gets too high, it could cause the output transformers to arc inside. The worst is no load at all.

Looking at the manual, it appears that there is only one output tap, which is stated to be optimized for 5 ohms, consistent with the comment by Rrog.

My GUESS is that using a 16 ohm speaker on an output tap that is optimized to work into a 5 ohm load does not represent a disparity that is large enough to cause amplifier damage, that can result from "inductive kickback" if a reasonable load is not connected to a tube amp that has an output transformer.

However, Hifitime and Ghostrider are correct that power output will be reduced. The amount of reduction will depend on the feedback setting you use and your choice of UL or triode mode (since both of those things affect the amplifier's output impedance), and the impedance of the speaker. On a percentage basis, the worst case reduction will probably occur where output impedance is lowest, which in this case is 1.28 ohms occurring for the maximum feedback and triode mode settings. According to my calculations the corresponding reduction into a 16 ohm load may be as much as approximately 3.75 db. That represents a loss of more than half of the amp's power capability, compared to a 5 ohm load driven with those settings.

Sonics may also be adversely affected by the mismatched loading of both the output transformer and the output tubes. Ringing may occur in the transformer, at least to a small degree, and the distortion performance of the output tubes may not be optimal.

As has been said above, high speaker impedances can certainly be advantageous, but not if the impedance is severely mismatched to what the amplifier is designed to drive.

All of that said, though, touching base with Manley as suggested earlier would certainly seem to be in order.

Regards,
-- Al