Be very carefull!! The impedance of this power attenuator is not what you want for your amplifier!
On the 4ohms tap you end up with 2,5ohms with the speaker level at max, which is very dangerous for your amplifier!!! When the level is at 0 you've got your 4ohms, but if you crank the volume past 12 o'clock you have less than 3ohms and the more you crank the less impedance you have and it give you 2,5ohms at full volume, so at the end it's a great device to fry your beloved tube amplifier if that's what you're looking for...
The 16ohms setting go to 11,5ohms when cranked to its max, so ideal for this one too.
The only one that can be use safely is the 8ohms tap, you start with 8ohms with the volume knob at 0 and 6,8ohms at full volume. It's perfectly acceptable and pretty safe for your amplifier.
The last issue with this power attenuator is the fact you can't use the line level output when the speaker volume is at 0 which is pretty useless... But you can easily modify that by swapping the resistor that feed the line level knob. Stock this resistor is solder on the center lug of the speaker volume potentiometer (with the blue wire), you have to desolder it and resolder it on the first lug with the yellow wire. Like that you will have volume at the output of your line level even when the speaker level is all the way down!! Easy fix, but you shouldn't have to do it, it's a conception flaw...
So as you can see this power attenuator have a bunch of problems, some you can fix and some you cannot, and potentially you can destroy your amplifier!!! That's definitly not a product I will advise to somebody who can't open it and modify it, and to be fair you shouldn't have to do it on a new product! So keep that in mind, be wise when you choose it (if you still want to buy it) and when you use it...
All in all the product do its job but it's pretty hazardous. Now you are aware!
