Rectifier Speaker connection

[lhrocker]

I was looking at the speaker connections section of the 3 ch Rectifier manual and it says a safe mismatch is to put a 16 ohm cab into the 8 ohm jack and a 8 ohm cab into the 4 ohm jack. Is it possible just to put the 16 in the 16 and the 8 into the 8?

 

[screamingdaisy]

I was looking at the speaker connections section of the 3 ch Rectifier manual and it says a safe mismatch is to put a 16 ohm cab into the 8 ohm jack and a 8 ohm cab into the 4 ohm jack. Is it possible just to put the 16 in the 16 and the 8 into the 8?

Nope.

 

[94Tremoverb]

You would think so, if you didn't know... it looks like both cabs are correctly matched.

But it's one of the few that isn't, because what roughly happens is that *both* cabs try to draw the full power (because each is correctly matched to its OT tap), with the result that the output tubes try to produce up to double the power (bad for them) and the 8-ohm section of the OT winding - which carries the current for *both*, because it's part of the 16-ohm winding, not separate - is overloaded.

There are two ways of running an 8 and a 16 ohm cab together - either as Mesa says, 16 from 8 and 8 from 4, or you can simply run them in parallel and treat them as a 4-ohm load (it's really 5.33 ohms, but close enough) and connect both to the 4-ohm jacks. I think this sounds a bit better, but 2/3 of the power goes to the 8-ohm cab... which may or may not be a good thing, depending on the cabs.

 

[lhrocker]

You would think so, if you didn't know... it looks like both cabs are correctly matched.

But it's one of the few that isn't, because what roughly happens is that *both* cabs try to draw the full power (because each is correctly matched to its OT tap), with the result that the output tubes try to produce up to double the power (bad for them) and the 8-ohm section of the OT winding - which carries the current for *both*, because it's part of the 16-ohm winding, not separate - is overloaded.

There are two ways of running an 8 and a 16 ohm cab together - either as Mesa says, 16 from 8 and 8 from 4, or you can simply run them in parallel and treat them as a 4-ohm load (it's really 5.33 ohms, but close enough) and connect both to the 4-ohm jacks. I think this sounds a bit better, but 2/3 of the power goes to the 8-ohm cab... which may or may not be a good thing, depending on the cabs.

Running them both into the 4 may be the way to go. One cabinet has C90's/V30's while the other cab has a quad of GM-70

 

[94Tremoverb]

Which way round? If the C90/V30 cab is 8 ohms and the G12M-70 is 16 (which is what I'm guessing) it probably won't work well, because 2/3 of the power will go to the C90/V30 cab which is already 3dB more efficient... you would want it the other way round, to equalize the volume. You can try it anyway (no harm will occur) but expect to find it a bit unbalanced.

If it does, go back to the Mesa method which distributes the power equally.