Futterman. Jump in? Or, not so fast...

Roger Modjeski (Music Reference) held the Futterman OTL in high regard (the Quad ESL as well), and his RAM Tube Works has the tubes needed for them, computer tested, graded, and matched.

But Modjeski designed an amp using the Quad as the load, and is another great amp for the speaker: The Music Reference RM-10 (original, or Mk.2). Only a single pair of EL84's per channel for 35 watts per. Much cheaper to retube than a Futterman, and in the RM-10 the 84's last 5,000-10,000 hours.

Awesome @roberjerman! State-Of-The-Art in the 60’s, and still great. One of Modjeski’s last designs was an ESL loudspeaker and a direct-drive OTL amp with which to drive it. No amplifier output transformer, no ESL input transformer, the tubes drove the ESL stators directly!

On his Audiocircle Music Reference Forum Roger discusses the design of the Futterman OTL, which he considered brilliant. Breaking current thinking on the subject, it employs very large amounts of negative feedback, one benefit being very low output impedance (in contrast to the high output impedance of all other OTL's).