Tube amps and speaker ohms


In your opinion , do push pull amps work better with 8 ohms or 4 ohms. .I am under the impression the lower the ohms, the more power is demanded from the amp....Another question, are there low powered SET amps ,and high power SET amps?
I'm looking at a 40 watt 845 tube amp for my 8 ohm, 89 db speaker.. just cked the Thor has a 86 db W18 midwoofers(2 per cabinet) and a 88 db tweeter. Will an 845 amp rated 40 watts be able to drive the 86/88 db speaker? With authority, bass, mids, highs, in dynamic sound stage? Synergy? Or poor match?
bartokfan
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
Thought id throw this in there. Schweikert vr-8. 4 ohm with a dip at 3ohm lowend. 96 db W 1 watt. 300B X4 mono blocks 50 watts each. Clipped the dooit out of them on medium levels.
Rogue 120 monos drove the heck out of them 120 watts.
Hiend, well sure the 300 tube, even at 4 per mono block are not a tube for 4 ohm speakers. So If it takes a beefy amp like Roge, then you lose some finesse somewhere. IOW the delicate 300 monos has the finesse that the Rogue lacks.
btw why mention 96 db at 1 watt? I never fully understood the db thing. I have a general idea ofdecibels at a certain distance.
+++ 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. +++

All things equal I'd go for a higher impedance speaker, yes, but you are quite mistaken by making an across the board statement that tube amps do not like 4 ohm speakers. Decware has some speaker models rated at 4 ohms that are more suited to tube amps than 99% of all 8ohm rated speakers on the market today, and that no exaggeration.

+++ Push pull's , like SET amps can be picky on what speakers they prefer, for best potential.
I'll stay with 8 ohms. +++

A SET amp by definition is single ended and as such not push pull. I do agree that any tube amp, be they single ended or push pull are picky on what speaker they prefer. Where I disagree with you is that nominal impedance has little bearing whether a speaker is suited for use on tube amps. The actual impedance curve and crossover design are way bigger factors you need to consider.

Regards
Paul