Tube Amp settings: Triode vs UL; 8 ohm vs. 4 ohm ?

There is no harm in trying either 4 or 8 ohm taps, and likewise either triode or ultralinear operation.  You are the only one who can say what sounds the best to your ears and in your particular setup.  Are you sure it is an EL 84 amp?  With that name I would guess that it is a KT88 amp.

They run KT88. EL84s and 6922. 87% efficient. They can run out of gas with a low efficiency speakers with yours at 90% they should play just fine. UL. If you can use 8 ohms valves will like it a lot better. Loose the bass duty it will be a one up, again.

Tubes amps don't do really well trying to control larger VC drivers. 4 ohms is even worse. KT88s will take up a little slack though.. Learn to bias correctly.. Best thing you can learn right now... UL, bias cool, try 8 ohms, loose the bass.. :-) Cary is fun.

I'm looking for another V12R (Red). I have a pair of SixPacs too. 6V6, 6L6, KT66, 6550, EL34, KT77, KT88, KT90, KT99 all work in both units. The V12 will work with 4, 8 or 12 valves. They work very well from 17 wpc to over 100 wpc. Great amps..

Regard

If you select the 4 ohm tap, you will be selecting a higher turn ratio for the output transformer of the amp.  This should tighten up the bass and reduce frequency response variations caused by the amp’s interaction with the varying impedance of the speaker.  But, there is a cost to using this tap instead of the 8 ohm tap, which is the amount of power that can be delivered to the speaker is lower.  Generally speaking, the best tradeoff would be to use the 8 ohm tap for speakers rated at 8 ohms and the 4 ohm tap with 4 ohm speakers.  However, the ratings are somewhat loose, so it doesn’t hurt to try the ‘wrong” tap.

A lot of people prefer triode operation over ultralinear for sound quality (smoother, less brittle sound), but the cost is lower output.  I have only heard a few amps where such a switch can be made for a direct comparison and I don’t recall liking triode operation that much more than ultralinear.  Again, give both a try.