SET vs OTL

I know the Duevel line fairly well. What I would like to know is how low the impedance actually goes and with what type of swing. I agree that using an auto-former somewhat defeats the purpose of an OTL and would not be an option for me.

For the record I have heard Atma-sphere, Joule Electra, Berning quasi-OTLs, the older Tenor, Transcendent Sound and Einstein. 

I also have auditioned/owned several P.P. designs from Thor Audio, VTL, EAR, VAC, French company I cant remember that was famous for CD players and SETs using 845s, 2A3s, 45 and 300Bs. Granted no SET design that was over $ 20K. 

I believe that each type of amp share many similar sonic characteristics. But removing the transformer is always a plus if you can feed the amp its entre of choice. 

The best SET amp I have heard was an old Mastersound made 32B integrated amp running only an an amplifier.

@audition_audio,

the higher the impedance, the better for OTLs. On the Graaf, the autoformers gave a marked improvement to going without. Old speakers used to be 16 ohms which would be ideal for OTls, however most modern designs have impedance dips under 4 Ohms with which OTLs have a hard time The Duevels in this regard are relatively benign and an easy load.

P.S. Push pull designs and SETs are very different, The overtone characteristics of SETs make for a much more nuanced and colourful sound. The differences tend to be most pronounced via horn designs. Obviously pp is higher output.

 I agree that using an auto-former somewhat defeats the purpose of an OTL and would not be an option for me.

 Correct using a "Zero" type autoformer is a "bandaid fix" for an OTL amp that is not suitable for that speaker loading, far better off getting the right amp.
OTL's that tend to suit speakers without having to use autoformers, then speakers then are mostly not that accurate, like I said it's a "catch22" 
If you still want to use P/P tube, to use a P/P tube amp that has a "proper output transformer" as part of the amps design and feedback configuration.

Cheers George