Speaker impedance

[steinros]

What may happen to a tube amp if you use a lower impedance speaker than recommended? (8 Ohms instead of 16)

[pdf64]

The max power output will probably be a little lower and the sound character may change a little.
There may be more ripple on the power supply at high output levels, which may cause ghosting.
The plate dissipation of the output tube/s may increase, especially at higher output levels, which may reduce the working life of the tube/s.
Pete

[Stevem]

Any impedance mismatch in regards to a tube amp with a output transformer will drop your output wattage by pretty much 1/3rd.
This will make for 1/3rd less clean head room before clipping. 1/3rd less output tube life if they are driving a lower impedance like in your case, and the drop in output wattage of 1/3rd will make for about a 15% drop in volume.
Sonic wise the bottom end response will be a tad looser.

[steinros]

Thanks. I was afraid of something like that. But I mean to remember that I once read that Carlos Santana used to play his Mesa Boogie through a speaker with lower impedance than recommended. Perhaps I misunderstood.

My problem is that I have a 12" cabinet that I would like to use with different amps. Now there is a 16 Ohm speaker for my little Peavey Classic 20 in it, but I would like to have the possibility to use it for my Super Champ which has an 8 Ohm output as well. Would it be possible to place a switchable big 8 Ohm resistor, either in parallell with a 16 Ohm speaker, or in series with an 8 Ohm speaker?

Thanks

[Teleguy61]

Just use the damn thing, it's not going to hurt anything.

[Stevem]

Look at playing thru a different impedance speaker like playing thru a attenuator.
it's the safest for the amp to have lower impedance speaker hooked up to a higher impedance tap.

[tubeswell]

What may happen to a tube amp if you use a lower impedance speaker than recommended? (8 Ohms instead of 16)

A lower impedance shifts the load line upwards and to the right, and depending on where your bias point is, can put the tube over the maximum recommended plate dissipation curve (which shortens tube life).

But it usually won't harm your amp to run it '1 knotch' above or below the optimum load resistance in the short term. If you notice any funny/random changes in output volume or warblyness or random crackling staticky noises, then that's the time to put new output tubes in.