This is very amplifier dependent!
Generally speaking, its to your advantage to run a higher impedance speaker, regardless of the amplifier you use.
With most tube amps (unless they are OTLs) you are dealing with an output transformer. Transformers are inductors and so they have certain properties. One of them is that they have to be properly loaded for lowest distortion. When you run the amp with a 16 ohm load on the 8 ohm tap, the amp is 'lightly loaded' as Roger Modjesky likes to say. The problem is that the transformer will 'ring' (harmonic distortion due to overshooting for those more technically minded) unless it is loaded correctly.
This is where the amplifier design is important- if the amp has a good deal of negative feedback (15 or more db) then the additional distortion will be mostly handled by the feedback. I say 'mostly' because' there is rarely a free lunch and this is one of those cases- I think while the bass will be OK, you may find it to be slightly brighter and harsher due to increased high frequency distortion, to which the ear is quite sensitive.
If the amp has no feedback, then the distortion caused by light loading will be obvious- and likely the 16 ohm tap will be preferred.
BTW, there is nothing even remotely unusual about a 16 ohm tap. FWIW, the output transformer operates more efficiently on the 16 ohm tap with greater bandwidth in both directions and better power transfer- so you actually gain a little power with lower distortion.
My 2 cents: shame on any amplifier company that does not have the taps available from the rear panel of the amp! They should always be readily accessible.
Generally speaking, its to your advantage to run a higher impedance speaker, regardless of the amplifier you use.
With most tube amps (unless they are OTLs) you are dealing with an output transformer. Transformers are inductors and so they have certain properties. One of them is that they have to be properly loaded for lowest distortion. When you run the amp with a 16 ohm load on the 8 ohm tap, the amp is 'lightly loaded' as Roger Modjesky likes to say. The problem is that the transformer will 'ring' (harmonic distortion due to overshooting for those more technically minded) unless it is loaded correctly.
This is where the amplifier design is important- if the amp has a good deal of negative feedback (15 or more db) then the additional distortion will be mostly handled by the feedback. I say 'mostly' because' there is rarely a free lunch and this is one of those cases- I think while the bass will be OK, you may find it to be slightly brighter and harsher due to increased high frequency distortion, to which the ear is quite sensitive.
If the amp has no feedback, then the distortion caused by light loading will be obvious- and likely the 16 ohm tap will be preferred.
BTW, there is nothing even remotely unusual about a 16 ohm tap. FWIW, the output transformer operates more efficiently on the 16 ohm tap with greater bandwidth in both directions and better power transfer- so you actually gain a little power with lower distortion.
My 2 cents: shame on any amplifier company that does not have the taps available from the rear panel of the amp! They should always be readily accessible.