Hey,
JP is fighting the registration spam-bots so until he can respond and I will handle many of the technical questions in the meantime.
The speaker cabinets are made by a craftsman in Maryland to this specific project.
In the original '57 design a single amplifier drives an input transformer that steps the signal up to feed a high impedance passive crossover which directs the music to the appropriate panels.
JP's 57's use a line level crossover integrated into a pair of push pull 300B amps loaded with step-up transformers tailored to the panel frequency response. JP has added some additional subtle crossover shaping to the panels directly. One key aspect is the dual 300B amps reside in the base of the speaker to avoid the need to step down the voltage to drive speaker cables to then step it back up to drive the panels. In a typical situation the output of a 300B will see a 25:1 step-down to get to 'traditional' speaker level. This is then stepped back up by a factor of 70 for the highs and 280 for the bass to drive the electrostatic panels. This instance has a pair of 300Bs feeding a 1:2 output transformer to drive the HF panels and a second pair feeding a 1:8 to drive the bass panels.
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dave