SET amp recommendation

Great information! Thank you

If the 12 ohm load of the zeroformers remains relatively flat a 300b amp would love this load. If the amp has "good" quality transformers and P.S. as audiofeil mentioned earlier, I believe 91db speakers in a smaller room at normal listening levels will be fine. 1500.00 budget does limit choice to some degree(good transformers and P.S. are`nt cheap).

I have used my 300b SET amp with 89 db speakers(8 ohm) in a friend`s system(large room) without any promblems what so ever.

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If the 12 ohm load of the zeroformers remains relatively flat a 300b amp would love this load.

As long as you can live with the loss of power. I believe these calculations are correct.

from 12 to 4 ohms is 3:1 for the impedance ratio

take the square root of 3 to get the voltage ratio = 1.7

If you have an 8W 300B amp you have 8V at the 8 Ohm tap (8V squared divided by 8 ohms = 8W)

divide that 8V by 1.7 to get 4.6V which will get you a little over 5W max.

maybe, but that's not a lot to drive a speaker with a recommended power of 50W.

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Herman,
This much I know, my speaker is a 14 ohm load(94db efficient) and it is a splendid match with my 8 watt amplifier, sound levels usally 75-85db(in a 14x26x8ft room)If his speaker is truly 91db efficient and he listens at modest levels(his stated preferenc)i.e. around 60-75db range the speakers are only drawing fractions of a "watt" of power.
He says his room is small, With a good quality 300b amp he will be fine.

It`s my understanding/experience that tube amps like a higher ohm load that`s relatively flat.
Charles

12-12-11: Herman
As long as you can live with the loss of power. I believe these calculations are correct....

Not that it makes much difference, but the power loss will be a bit less than what you calculated. Since the output impedance of a SET amp is significant, it will be able to put more voltage into 12 ohms than into 8 ohms. Output impedances that I recall seeing for 300B SET amps range from around 2 ohms to around 5 ohms, corresponding to damping factors of 4 to less than 2.

Taking as an example an output impedance of 4 ohms (damping factor 2), I calculate that the 8W capability into 8 ohms would be reduced to 6.75W into the 4 ohm load through the autoformer's 3:1 impedance transformation.

Best regards,
-- Al