I’ve been asked this question several times in as many days so it seems like a good time to discuss the question. I’ve previously mentioned how the proper speaker load is important as well as matched speaker impedances in a multiple speaker configuration, so we don’t need to cover that again. This is directed towards amps that have individual speaker output jacks for their various speaker impedance options. There are more transformers being offered now with two or three different impedance options, and for this discussion we’ll use the 5E3 D-Lux for an example as I do carry some tweed Deluxe output transformers with 4/8/16 ohm output taps. Although there is room for all three output jacks on the chassis I’m usually just asked for the 4 & 8 ohm taps. So the basic question that’s asked is if I have both a 4 ohm & an 8 ohm output jack, can I plug a 4 ohm speaker into the 4 ohm output & then also plug an 8 ohm speaker into the 8 ohm output.
The simple answer is that it’s not recommended as it places an odd load on the output transformer. Once again, the 4 ohm speaker offers the least resistance so that’s where the majority of the signal will be going as well. So between the unusual strain it places on the output transformer and the fact that you probably wouldn’t be happy with the result anyway, it’s better to stay within the design limits of the output transformer.
The 4 ohm output would be used if you had a 4 ohm speaker load like a favorite speaker that you can’t live without but it’s a 4 ohm unit. Another scenario would be an 8 ohm internal speaker & an 8 ohm extension cab, and then you’d want to use a 1/4″ female speaker jack wired off the internal speaker. If you were just using an 8 ohm internal speaker then you’d want to plug into the 8 ohm output.