Speaker load on tube amplifier...

@atmasphere Super helpful, thank you. I have read your comments on speaker ohm rating many times. I comprehend your perspective, and I find it interesting that the engineer of my speakers praises the 4ohm load, for other reasons. It seems what is lacking here is a "whole" approach to the various designed decisions, which seems to be much more complex.

So, lower plate load is better, from what I'm hearing you say, and this is because it's easier on the amp, less current to control, less heat to wield? 

@millercarbon Do you have a good resource for describing the sound quality of various tubes? Maybe there is a breakdown here on A'gon.

@freediver Thanks for your informative post... the speakers are either 95db or 98db at 4ohms. There's some confusion in reading the stat. These are Tekton Moabs. So, I think the amp could fit... 

So, lower plate load is better, from what I'm hearing you say, and this is because it's easier on the amp, less current to control, less heat to wield?

@listening99


Not in this case- the reason I would go with the 7581/6L6 is that apparently the output transformer is set up so that it presents a reasonable load to a variety of power tubes, each of which work best with different impedance. Since the KT88 wants to see a higher load impedance, this means that the transformer is probably loading the 6L6 at that higher impedance too.

Now transformers are called that because they transform impedance, but that works both ways. So if you put a lower impedance than 4 ohms on the 4 ohm tap, the power tube will see a lower impedance too. But if the power tube is normally seeing something that is a bit higher than is optimal (for power output reasons) when the speaker load is lower the amp will respond by putting out *more power* which is actually what you want it to do when that lower impedance (3.1ohm dip) is encountered. So the 6L6 will allow you to do that, while the KT88 probably will be less likely to do so (and also will make higher distortion).