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
My JOR is,, well the one I sold...is rated 40 watts "conservatively" as they say...does "manage" to drive the 89 db speakers. However since i never biaed the unit, I am not sure there was more highs it could have achieved. On jazz, pop, R7B there was authority. In big complex orch I was always looking for more authority. So the 40 watts was never enough to make the orch "bloom". This is the only reason I sold the amp and looked for more power. I was say a "normal" 40 watt tube amp is not going to deliver the goods on a 89 db speaker. I always felt there was more in the orch that was not comming through.
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The guy who bought my JOR , who actually owned 2 previous JOR's said the amp "should/ought" to be biased every year. Take that up with him. I figured he knows what he is talking about. said tubes wear every yr and a slight bias adjustment 'could be made". Obviously take all my posts as though i am a learning newbee. I hope no one takes anything i say with too much seriousness. Just ideas to open discussion. We can all learn something here. You too.
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Tvad, all the time I had the JOR i never thought to bias the unit to see if I could get a tad more highs. Now that i have the Defy 7, if there is something I don;'t like about the sound, i'll look into biasing the unit. But since the amp has few hours on it, should I bias the amp? It should be biased correctly with few hours use. I've never heard tube amps need biasing regularly. I should look into how to bias the defy 7. Not even sure how to go about it. There is a wooden board at the bottom. Will have mt tech friend assist me first time.
Also I learned the JOR had a pre out and never took advantage of in use with a sub. I will have Tyler replace the woofer in his Taylo with a Seas Excel W26. And so will keep my Thor's, which I had for sale 3 days last week.
The things we learn, one must research and think for oneself of all the options avaliable.