SET vs OTL

@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

P.P.S

The French company might have been Jadis or Audioaero, both of which build good amps.

BTW, both on OTLs and on SETs low capacitance speaker cables are clearly preferable, think Shindo or similar