How about an OTL that can drive a wide variety of speakers properly?Here is an interesting story that happend to me. Jim Jordan, the designer of Vaughn speakers fell in love with the Wavelength 300B Cardinal with silver transformers and all. Big bucks for a 7 watt amplifier. This amplifier has rather low damping, but within its power range I assume it to be a good amplifier. He named his speaker after the amplifier. In this case the amplifier came first and he designed a speaker he felt worthy of it as other speakers he tried were not.
No such thing, unless you stick an autoformer band-aid on it for the hard to drive ones. Then you ruined the whole advantage of the OTL design and what it can do.
Your better off getting one of your amps to do the job if you wish to stick with tubes, or putting a proper output transformer on the OTL, again a backward step to what an unhindered OTL is capable of giving with the right speaker.
https://www.vaughnloudspeakers.com/story
Then he met me, actually I went to his house to hear his speakers. I took along a rough prototype of my OTL for him to hear. Somehow he convinced me to make one for him and one for his customer in stereo on a nice chassis. Now he uses my AUTOFORMER OTL all the time. It has very low distortion very low output impedance. It is of the Futterman School which always has low output impedance. Mine only two output tubes, triode connected, and one driver tube per channel. Most OTLs have 6-12 output tubes per channel. Lots of heat, lots of matching.
The autoformer has no special materials, I make them of standard copper magnet wire and M6 Iron. It is very small, costing a fraction of a silver 300B transformer. It is partially in the feedback loop or not, as desired. Id does effect the sound and Jim moves it from time to time for different listening. He likes the subtle changes it makes.
I wound 4, 8, 16 ohm taps and 32 ohms is direct output. At 32 ohms the amplifier puts out 30 watts into a 32 ohm load. An 8 ohm load connected to the 32 ohm tap produces 3 watts because the tubes can only provide that much current (about 1 amp). But any load connected to its proper tap will put out 30 watts. To my suprise the Autoformer extends the high frequency frsponse from 120 KHZ direct to 160 Khz using the 8 ohm autoformer tap into an 8 ohm load, or 4 into 4, etc. All the taps produce the same results into their specified load.
I arrange a feedback wire on a lug and tell the user to move the feedback wire to whichever tap they are using so the feedback is always on the tap looking right at the speaker. Sometimes the put it on a different tap and like that better. Its all good, the amp is stable and happy.
In closing the SA-6 I deisgned for Counterpoint and the large Futtermans will drive a wide variety of speakers with 100 watts per channel with very low distortion and high damping. Keep in mind that the Circlotron amplifiers are an entierly different animal. They do not have low output impedance of a lot of current. All OTLs are not the same
I invite George and others to take a little time and learn about the Futterman style amplifiers and then say something. Little by little I will get around to all of it, but it took me years to fully appreciate his work, the man was very smart and I am happy I got to spend an afternoon in his shop.