Tube amps and speaker ohms

Newbee's first point on the impedance curve of the speaker is taking you to where you really need to be. I'll add in phase angle as well.

One other parameter I think that should be discussed is the crossover topology. How simple or complex the crossover is makes a tremendous impact into whether the loudspeaker presents an easy or difficult load. Tube amps like first order crossovers better than second order crossovers, and second order crossovers better than third order crossover, and on and on. On top of that, things like Zobel networks, trap circuits, and the like can turn things completely on their head. Take some famous loudspeakers, such as Thiels, with first order crossovers that so many compensation circuits - a total bear to drive.

The best generality I can offer is that you want the crossover as simple as can be. The opinions on single driver loudspeakers being a good match with a tube amp is true - because there is no crossover to suck up the power. Of course, you do give up frequency response.

Far too often, sensitivity and nominal impedance give such an incomplete picture that you simply need to walk away from what people will tell you, and give it a try. THAT is the only way you'll know...

Well, I'm trying a brand new experiment today, and for the next couple of weeks. Trying a 30wpc Leben CS600 with my 89db/6 ohm (3.5 ohm minimum) VR4 Gen III HSE loudspeakers. Theoretically, this should not be a great match even though the Leben has a 4 ohm setting. Mid week a pair of 88.5 db/8ohm (5.5 ohm minimum) Castle Howard speakers arrive. Later in the week, a 55wpc Rogue Cronus arrives.

Yes, major system changes afoot...

Trelja,

Sure glad you can read thru my lack of editing skills. For others, last words in 1) "(curve of the amp)" should read (curve of the speakers).

Glad I don't get paid for this! :-)

Hi Pauly, here's what's up with four ohms: Yes, you can use the 4 ohm tap, but at a price. On most output transformers that have a 4 ohm tap, measuring the response of the amplifier on that tap as opposed to the other taps will reveal slightly lower power and quite a bit less bandwidth (both due to increased turns ratio and distributed capacitance in the windings). Sometimes there is also additional hysteresis loss. So tubes amps can make lower distortion on higher impedance taps as well.

So, all other things being equal, most tube amps will sound better on 8 or even 16 ohms as opposed to 4.

Trelja, Good answer. Looking at the Thor's crssover designed by Appolito, one can see a simple yet effective design. The thing "just looks right". Its not loaded down with lots of components. Dr Appolito seems to know how to get the most music of the Seas Excel. And he did so successfully.
Newbee I realize that hypothetically it should not matter whether its a 4 OR 8 ohm laod for a "well designed tube amp". But realistically, most tube amps have their limits, depending on how well the trans are made AND the push pull tube on the block. Each tube sings differently and reacts differently to the ohm level. I refer specifically to 4 and 8 ohms, to keep things simply, disregarding 6 ohms.
Ideally tube amps work best on a 8 ohm load. Sure my JOR has driven one beast of a speaker and one moderately heavy load at 4 ohms, which was the Tyler Lin Sig Sys. But the JOR is not built for such loads over a long haul.
Pauly "4 ohms should not be any problem for a tube amp". But in my experience tube amps do not like 4 ohms, especially when the music gets complex, as in orch, even large jazz ensemble is rather thin sounding.
Push pull's , like SET amps can be picky on what speakers they prefer, for best potential.
I'll stay with 8 ohms.
The Tyler Lin Super Towers(8 ohm) is now on my radar and the Tyler Lin Sig Sys(4 ohm) is off.
Thanks Joe for that fine post, crossover network gets overlooked too often. I, like you, want to see whats inside the box BEFORE i buy.
A sealed speaker does me no good. Even if I don't know how the hell a crossover is made.
Paul
Baton Rouge