Another amp-speaker(s) ohmage question

[Jon Silberman]

OK, I understand that I plug an 8 ohm speaker into my Hellhound's 8 ohm output and two 8 ohm speakers (using Reverend's provided speaker Y-chord) into the 4 ohm output.

What I don't understand (not what, but why and how?) is this (from the Hellhound owner's manual), can anyone explain how and why this can work? (It just doesn't feel right that you should be able to tap the tranny at two places at the same time!)

>> Cabinets with different ohm ratings can be used at the same time, as long as the ohm rating of each cabinet matches the ohm rating of each jack.

[John Phillips]

That is exactly what NOT to do according to Mesa (and which fits with current calculations).

Running both impedance taps at the same time into their matching loads is a bad idea because the 4-ohm tap is just that - it's a portion of the 8-ohm winding, not separate. This means that the 4-ohm portion is taking not only the current for the 4-ohm load, but also that for the 8-ohm as well.

Unlike when you run a 4-ohm load from an 8-ohm setting, the maximum power is still transfered as there is no mismatch to reduce it. So you're running much more current than normal.

I would not do or recommend that.

If the Hellhound's manual states that you can, maybe they have used a heavier-duty transformer to cope with the extra load... but you'll still be stressing the tubes very heavily.


The way it is advised in the Mesa manual is that you can use a 16-ohm load on the 8-ohm tap and an 8-ohm load on the 4-ohm tap at the same time, which if you do the math works out as the correct load on the transformer.


BTW, it's "cord", not "chord" ;) :).

[Jon Silberman]

Originally posted by John Phillips
BTW, it's "cord", not "chord" ;) :).

To paraphrase Scottie: "Captain, I'm a guitarist, not a spelling bee champ." :angel

[Jon Silberman]

Seriously, thanks very much (as always) for the technical info., John. :)

I've posted a link to this thread on the FDP's Reverend Congregation asking Joe, if he has the time, to have a look and share his reactions. I'll let you know what he tells if he responds.