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

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.

I owned this amp in the past. You need to try the different settings and listen for yourself with your speakers to determine which settings and speaker taps work best.

With the Fortes you will more than likely prefer the 8 ohm tap.

Almost without fail, every switchable amp I have owned has sounded better in the UL or Pentode mode. Most manufacturers voice their amps in UL and add the triode setting as a marketing tool. But every ear is different. Try both and see what you prefer.

Oz

. But every ear is different. Try both and see what you prefer.

This is the simple truth.  +1 The recommendations to try both triode/UL mode and 4 and 8 ohm speaker taps. Purely an individual case by case preference as to what will sound better.

Charles

This amp runs KT88 as output tubes, EL84s as drivers and 6922s as input tubes.  I would guess that it would have enough grunt to operate in triode mode even if that means about half the output of ultralinear.  You could also consider operating in different modes for different music/listening conditions.  Personally, I don't like to fiddle, so I wouldn't do that, but it is an option.