SET amp recommendation

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You don't really have an SET friendly set up at least for your typical 2.5 watt 2A3 or 8 watt 300B amp. Doesn't your speaker manufacturer recommend at least 50 watts?

If your speakers are 91 dB 4 ohm and you multiplied it up to 12 ohms the trade off is you get less power delivered to the speaker. The maximum voltage output of the amp is what it is but the autoformer divides this down so less gets to the speaker.

Fine if you have power to spare but starting with a low power amp and a medium sensitivity speaker you do not. I don't see any advantage to the autoformer if you choose a tube amp that has a 4 ohm tap.

Certainly no harm in trying.

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Based on your speakers and price point, I think a used 300B is probably the most likely candidate for you. I don't think you will be happy driving your speakers with lower powered SET amps 45/50/2A3.

Another potential option is to keep checking ebay as periodically Sean Casper offers F2a amps in that price range. The Siemens F2a tube (made famous in German Klangfilm amps in the 1950's) has about the same power rating as the 300B but has a completely different sonic signature. It is a much more dynamic sounding tube with better bass. It also has a wonderful presence to it - it comes across as a much more powerful tube. What it does give up to the 300B is some midrange sweetness and a bit of nuance. Both would be very good alternatives to your OTL.

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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